JP4285019B2 - Transparent conductive thin film and method for producing the same, transparent conductive substrate for display panel using the same, and electroluminescence device - Google Patents

Description

【００７３】
表１から明らかなように、本発明のタングステンを含有した酸化インジウムからなる試料１〜８の結晶質の透明導電性薄膜は、全て比抵抗が８.８×１０^−４Ωｃｍ以下であり、ほとんどが６.０×１０^−４Ωｃｍ以下と低かった。試料１〜８の加熱処理前における非晶質の各透明導電性薄膜では、比抵抗が４.１〜９.５×１０^−４Ωｃｍであったが、加熱処理により結晶化されたことによって比抵抗が低下したことが分る。例えば、タングステン含有量５.６原子％の試料５では、加熱処理前における非晶質の膜の比抵抗は４.８×１０^−４Ωｃｍであるのに対し、加熱処理後における結晶質の膜では３.６×１０^−４Ωｃｍに低下した。
【００７４】
また、上記本発明の全ての試料で膜表面の表面粗さは、中心線平均粗さＲａの平均値で２.１ｎｍ以下であり、非常に平滑であることが分った。尚、加熱処理前の非晶質の各透明導電性薄膜においてもＲａは１.４〜２.０ｎｍと非常に平滑であり、加熱処理により結晶化された後においても優れた表面平滑性が維持されていることが分る。更に、膜の平均可視光透過率は８５〜９４％であり、透過率も良好であった。波長４００ｎｍにおける膜自体の光透過率は、加熱することによって１０〜３０％ほど増加し、加熱前の非晶質膜と比べて短波長側の透過率が改善された。
【００７５】
尚、上記実施例では結晶化のための加熱処理を窒素雰囲気中で行ったが、アルゴンなど他の不活性ガス中や、真空中あるいは大気中で結晶化のための加熱処理を行っても、上記と同様の結果が得られた。
【００７６】
実施例２
Ｉｎ_２Ｏ_３粉末と、ＷＯ_３粉末及びＳｉＯ_２粉末を用いた以外は、実施例１と同様にして、タングステン及びシリコンを含有する酸化インジウム焼結体ターゲットを作製した。また、このターゲットを用いた直流マグネトロンスパッタリング法により、実施例１と同じ条件で成膜を行い、タングステンとシリコンを含む酸化インジウムからなる透明導電膜を作製した。
【００７７】
このように作製した透明導電性薄膜は、非晶質であることがＸ線回折測定で確認された。このタングステンとシリコンの含有量が異なる酸化インジウムからなる種々の透明導電性薄膜について、大気中にて３００〜４５０℃で１０分間加熱処理を行い、結晶質の透明導電性薄膜を作製した。膜が結晶化していることは、実施例１と同様にＸ線回折測定により確認した。
【００７７】
得られた本発明のタングステンとシリコンを含む酸化インジウムからなる結晶質の各透明導電性薄膜について、実施例１と同様に、タングステン含有量とシリコン含有量（共にタングステンとシリコンとインジウムの含有量の合計に対する原子％）、比抵抗及び中心線平均粗さ（Ｒａ）を測定し、その結果を下記表２に示した。尚、組成分析の際に用いた基板は、実施例１ではシリコンウエーハーであったが、ここではゲルマニウムウエーハー（純度９９.９９％）を用いた。
【００７８】
【表２】

【００７９】
上記表２から明らかなように、本発明のタングステンとシリコンを含有した酸化インジウムからなる試料９〜２０の結晶質の透明導電性薄膜は、全て比抵抗が８.６×１０^−４Ω・ｃｍ以下と低く、加熱処理前の非晶質の膜よりも比抵抗が低下した。また、全ての試料で膜表面の中心線平均粗さＲａの平均値は２.２以下と非常に平滑であり、加熱処理前における非晶質の膜のＲａ１.１〜１.９ｎｍという優れた平滑性が維持さていることが分った。更に、膜の平均可視光透過率は８５〜９３％であり、透過率も良好であった。尚、波長４００ｎｍにおける膜自体の光透過率は、加熱することによって１０〜３０％ほど増加しており、加熱前の非晶質膜と比べて短波長側の透過率が改善された。
【００８０】
尚、上記実施例では結晶化のための加熱処理を大気中で行ったが、真空中やアルゴンあるいは窒素などの不活性ガス中で結晶化のための加熱処理を行っても、上記と同様の結果が得られた。
【００８１】
実施例３
Ｉｎ_２Ｏ_３粉末と、ＷＯ_３粉末及びＧｅＯ_２粉末を用いた以外は、実施例１と同様にして、タングステン及びゲルマニウムを含有する酸化インジウム焼結体ターゲットを作製した。また、このターゲットを用いた直流マグネトロンスパッタリング法により、実施例１と同じ条件で成膜を行い、タングステンとゲルマニウムを含む酸化インジウムからなる透明導電膜を作製した。
【００８２】
このように作製した透明導電性薄膜は、非晶質であることがＸ線回折測定で確認された。このタングステンとゲルマニウムの含有量が異なる酸化インジウムからなる種々の透明導電性薄膜について、大気中にて３００〜４５０℃で１０分間加熱処理を行い、結晶質の透明導電性薄膜を作製した。膜が結晶化していることは、実施例１と同様にＸ線回折測定により確認した。
【００８３】
得られた本発明のタングステンとゲルマニウムを含む酸化インジウムからなる結晶質の各透明導電性薄膜について、実施例１と同様に、タングステン含有量とゲルマニウム含有量（共にタングステンとゲルマニウムとインジウムの含有量の合計に対する原子％）、比抵抗及び中心線平均粗さ（Ｒａ）を測定し、その結果を下記表３に示した。尚、組成分析の際に用いた基板は、ゲルマニウムウエーハー（純度９９.９９％）を用いた。
【００８４】
【表３】

【００８５】
表３から明らかなように、本発明のタングステンとゲルマニウムを含有した酸化インジウムからなる試料２１〜３２の結晶質の透明導電性薄膜は、全て比抵抗が８.７×１０^−４Ω・ｃｍ以下、ほとんどが６.０×１０^−４Ωｃｍ以下と低く、加熱処理前の非晶質の膜よりも比抵抗が低下した。また、全ての試料で膜表面の中心線平均粗さＲａの平均値は１.９以下と非常に平滑であり、加熱処理前における非晶質の膜のＲａ０.７〜１.７ｎｍという優れた平滑性が維持さていることが分る。更に、膜の平均可視光透過率は８５〜９３％であり、透過率も良好であった。尚、波長４００ｎｍにおける膜自体の光透過率は、加熱することによって１０〜３０％ほど増加しており、加熱前の非晶質膜と比べて短波長側の透過率が改善された。
【００８６】
尚、上記実施例では結晶化のための加熱処理を大気中で行ったが、真空中やアルゴンあるいは窒素などの不活性ガス中で結晶化のための加熱処理を行っても、上記と同様の結果が得られた。
【００８７】
実施例４
Ｉｎ_２Ｏ_３粉末と、ＷＯ_３粉末と、ＳｉＯ_２粉末又はＧｅＯ_２粉末と、ＳｎＯ_２粉末を用いた以外は、実施例１と同様にして、タングステン、シリコン又はゲルマニウム、スズを含有する酸化インジウム焼結体ターゲットを作製した。また、このターゲットを用いた直流マグネトロンスパッタリング法により、実施例１と同じ条件で成膜を行い、タングステン、シリコン又はゲルマニウム、スズを含む酸化インジウムからなる透明導電膜を作製した。
【００８８】
このように作製した透明導電性薄膜は、非晶質であることがＸ線回折測定で確認された。このタングステンと、シリコン又はゲルマニウムと、スズの含有量が異なる酸化インジウムからなる種々の透明導電性薄膜について、大気中にて３００〜４５０℃で１０分間加熱処理を行い、結晶質の透明導電性薄膜を作製した。膜が結晶化していることは、実施例１と同様にＸ線回折測定により確認した。
【００８９】
得られた本発明のタングステンと、シリコン又はゲルマニウムと、スズを含む酸化インジウムからなる結晶質の各透明導電性薄膜について、実施例１と同様に、タングステン含有量と、シリコン又はゲルマニウム含有量（共にタングステンとゲルマニウムとインジウムの合計に対する原子％）、及びスズ含有量（スズとインジウムの合計に対する原子％）、比抵抗及び中心線平均粗さ（Ｒａ）を測定し、その結果を下記表４に示した。尚、組成分析の際に用いた基板は、膜中にシリコンを含む場合はゲルマニウムウエーハーを基板として用い、膜中にゲルマニウムを含む場合はシリコンウエーハーを基板として用いた。
【００９０】
【表４】

【００９１】
表４から明らかなように、本発明のタングステンと、シリコン又はゲルマニウムと、スズを含有した酸化インジウムからなる試料３３〜４０の結晶質の透明導電性薄膜は、全て比抵抗が６.７×１０^−４Ω・ｃｍ以下と低く、加熱処理前の非晶質の膜よりも比抵抗が低下した。また、全ての試料で膜表面の中心線平均粗さＲａの平均値は１.９以下と非常に平滑であり、加熱処理前における非晶質の膜のＲａ０.９〜１.５ｎｍという優れた平滑性が維持されていることが分った。更に、膜の平均可視光透過率は８５〜９０％であり、透過率も良好であった。尚、波長４００ｎｍにおける膜自体の光透過率は、加熱することによって１０〜３０％ほど増加しており、加熱前の非晶質膜と比べて短波長側の透過率が改善された。
【００９２】
尚、上記実施例では結晶化のための加熱処理を大気中で行ったが、真空中やアルゴンあるいは窒素などの不活性ガス中で結晶化のための加熱処理を行っても、上記と同様の結果が得られた。
【００９３】
上記の実施例１〜４に示した本発明の各透明導電性薄膜において、加熱による結晶化処理前の非晶質膜は、弱酸性のエッチング液を用いてエッチング特性を調べたところ、全てエッチング速度が速く、また部分的にエッチングの浅い箇所もなく、エッチング特性は良好であった。その後、エッチング加工された非晶質膜を、各実施例と同様の条件で加熱処理を行い結晶化したところ、膜の表面平滑性、比抵抗、可視光透過率などの特性は、エッチングを行わずに評価した上記実施例１〜４とほとんど同じ結果であった。
【００９４】
比較例１
従来広く用いられているスズを含む酸化インジウム（ＩＴＯ）焼結体ターゲットを用いて、基板温度を室温にした状態で、スパッタリング法により、膜厚約１００〜３００ｎｍの非晶質の薄膜を作製した。スパッタリング時のガス組成及びガス圧、ターゲット−基板間の距離、ターゲットサイズなどは、前記の実施例１と同様の条件で行った。
【００９５】
得られたＩＴＯ薄膜について、Ｘ線回折測定と透過型電子顕微鏡及び電子線回折により確認したところ、非晶質の部分と結晶質の部分とが混在していることが分った。また、このＩＴＯ薄膜の中心線平均粗さ（Ｒａ）は、４.５〜６.６ｎｍであり、表面の凹凸が非常に大きかった。非晶質のＩＴＯ薄膜を、窒素ガス中で３００〜４００℃にて加熱処理を行って結晶化させた。膜が結晶化していることは、実施例１と同様にＸ線回折測定により確認した。
【００９６】
得られたスズを含む酸化インジウム（ＩＴＯ）からなる結晶質の透明導電性薄膜について、実施例１と同様に、スズ含有量（スズとインジウムの合計に対する原子％）、比抵抗及び中心線平均粗さ（Ｒａ）を測定し、その結果を下記表５に示した。
【００９７】
【表５】

【００９８】
表５に示すように、比較例である試料４１〜４６のＩＴＯ薄膜は、全て比抵抗が２.５×１０^−４〜６.６×１０^−４Ωｃｍであり、膜の平均可視光透過率は８５〜９０％で透過率も良好であった。しかしながら、膜の中心線平均粗さ（Ｒａ）は、４.８〜６.６ｎｍであり、本発明の実施例１〜４に示した膜と比べて著しく大きいことが分る。これら比較例では、加熱処理前のＩＴＯ薄膜における大きな表面凹凸が、加熱処理によってそのまま結晶化されたものと考えられる。
【００９９】
よって、これら比較例のＩＴＯ膜をＬＣＤ素子や有機ＥＬ素子の透明電極として使用するためには、その表面に後からエッチング又は研磨加工を施して、表面の凹凸を除去する必要がある。
【０１００】
更に、加熱前のＩＴＯ膜について、弱酸性のエッチング液を用いてエッチング特性を調べたところ、結晶相の部分にエッチングの浅い箇所が生じやすいことが分った。また、エッチング速度も遅く、上記実施例１〜４の膜と比べて１.５〜２倍のエッチング時間がかかった。尚、エッチング加工後に加熱処理を行って得たＩＴＯ薄膜は、エッチング浅さ残ったままであり、ディスプレイ用の透明電極として用いることはできないことが分った。
【０１０１】
比較例２
従来から使用されているＩｎ_２Ｏ_３−ＺｎＯ（１０重量％）の焼結体ターゲットを用い、実施例１と同様の条件で、亜鉛を含む酸化インジウムからなる透明導電性薄膜を作製した。
【０１０２】
得られたＩｎ_２Ｏ_３−ＺｎＯ薄膜は、非晶質構造であり、膜表面の中心線平均粗さ（Ｒａ）も１.２〜１.８ｎｍであり、表面平滑性は良好であった。また、膜の比抵抗も５.１×１０^−４Ωｃｍと低い値を示した。
【０１０３】
しかし、波長４００ｎｍ付近における膜自体の光透過率は２５％であり、実施例１〜４の透明導電性薄膜（７３％）と比較して明らかに劣っていた。このＩｎ_２Ｏ_３−ＺｎＯ薄膜をＸＰＳにて分析したところ、膜中に金属Ｚｎが含まれていることが分り、これにより波長４００ｎｍ前後での光透過率の低下が生じたものと判断される。
【０１０４】
また、このＩｎ_２Ｏ_３−ＺｎＯ薄膜を、窒素ガス中にて３００〜４００℃で１０分間加熱することにより結晶化を行った。しかし、結晶化された薄膜においては、波長４００ｎｍ付近の透過率が若干改善されたものの、本発明の実施例１〜４の透明導電性薄膜には及ばなかった。
【０１０５】
上記実施例１〜４及び比較例１〜２では、第１工程の非晶質膜の形成にスパッタリング法を用いた例を示したが、真空蒸着法及びイオンプレーティング法で成膜を行っても、全く同様の結果を得ることができた。
【０１０６】
【発明の効果】
本発明によれば、結晶質であって、可視光透過率が大きく、低抵抗であると同時に、表面平滑性に優れた透明導電性薄膜、及びその製造方法を提供することができる。この透明導電性薄膜は、表面が平滑で低抵抗な電極が必要とされる有機ＥＬ素子だけでなく、無機ＥＬ素子やＬＣＤ等の表示デバイス素子の透明電極として極めて有用なものである。
【０１０７】
従って、本発明の透明導電性薄膜を電極として用いた有機ＥＬ素子は、従来よりも発光輝度が高く、且つその輝度の半減期も長くなるうえ、ダークスポットの発生がなく、耐久性にも優れたものとなり、その工業的価値は極めて大きい。
【図面の簡単な説明】
【図１】本発明の有機ＥＬ素子の一具体例を示す概略図である。
【符号の説明】
１ 絶縁性基板
２ 陽極
３ 陰極
４ 導電性薄膜
５ 金属薄膜
６ 有機層
７ 発光層
８ 正孔注入層
９ 正孔輸送層
１０ 絶縁層
１１ 保護膜[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transparent conductive thin film having low resistance and excellent surface smoothness, a method for producing the same, and a transparent conductive substrate for a display panel and an electroluminescence device using the transparent conductive thin film.
[0002]
[Prior art]
The transparent conductive thin film has high conductivity and high transmittance in the visible light region, so it can be used as a transparent electrode for solar cells, liquid crystal display (LCD) elements, electroluminescence (EL) elements, and other various light receiving elements. Has been. In addition, it is also used as a transparent heating element for anti-fogging, such as a heat ray reflective film used for automobile window glass and building window glass, various antistatic films, and a refrigerated showcase.
[0003]
An electroluminescence element (hereinafter also referred to as an EL element) is an element that uses electroluminescence, has high visibility due to self-emission, and has excellent impact resistance because it is a complete solid-state element. It is attracting attention as an element. The EL element includes an inorganic EL element using an inorganic compound as a light emitting material and an organic EL element using an organic compound. Among these, since organic EL elements can be easily reduced in size by greatly reducing the driving voltage, practical research has been actively conducted as next-generation display elements. The structure of this organic EL element is based on a laminated structure of anode / light emitting layer / cathode, and a structure in which a transparent anode is formed on a transparent insulating substrate such as a glass plate is usually employed.
[0004]
As a transparent conductive thin film used for the EL element or the like, tin oxide doped with antimony or fluorine (SnO₂) Film, zinc oxide (ZnO) film doped with aluminum or gallium, indium oxide doped with tin (In₂O₃) Membranes are widely used. Among them, tin-doped indium oxide film, that is, In₂O₃The -Sn-based film is called an ITO (Indium tin oxide) film, and is widely used because it is easy to form a low-resistance film.
[0005]
As a method for forming an ITO thin film for a transparent electrode, a spray method, a vacuum deposition method, an ion plating method, a sputtering method, and the like are known. In many cases, a sputtering method is employed. The sputtering method is an effective method when a film is formed on a deposition target material (hereinafter simply referred to as a substrate) using a material having a low vapor pressure or when precise film thickness control is required. Since the operation is very simple, it is widely used.
[0006]
This sputtering method is generally performed under an inert gas atmosphere such as argon of 0.1 to 10 Pa, using a substrate as an anode and a target as a cathode, generating glow discharge between them to generate argon plasma, In this method, an argon cation is collided with a cathode target, whereby particles of a target component are blown off, and the particles are deposited on a substrate to form a film.
[0007]
Sputtering methods are classified according to the method of generating plasma such as argon. Those using high-frequency plasma are called high-frequency sputtering methods, and those using DC plasma are called DC sputtering methods. A method of depositing a magnet on the back side of the target to concentrate plasma directly on the target and increasing the cation collision efficiency even at a low gas pressure is called a magnetron sputtering method. Usually, a direct current magnetron sputtering method is adopted as a method for producing a transparent conductive thin film.
[0008]
Usually, in order to form an ITO thin film by sputtering, an ITO sintered body is used as a target. This ITO sintered body is obtained by a powder sintering method, that is, a method of substantially mixing indium oxide or tin oxide powder into a desired composition, press-molding, and sintering at a temperature of 1400 ° C. or higher. It is manufactured. Conventionally, tin oxide (SnO₂) Is contained in an ITO sintered body containing about 10% by weight, particularly a density of 7.0 g / cm.³However, recently, in order to improve the film forming performance of ITO, the development of a higher density ITO sintered body and a sputtering target using the ITO sintered body has been studied.
[0009]
As a high density ITO sintered body, the density is 7.02 g / cm.³A method for manufacturing an ITO sintered body with a variation of about 1% has been proposed (see Patent Document 1). However, when this ITO sintered body is used as a sputtering target, it is possible to form a film well in the initial stage, but as it approaches the end of the target use, blackened matter called nodules is generated on the target surface, causing abnormal discharge and the like. As a result, the sputtering rate decreases. This is because the pore distribution of the sintered body is not controlled, and the effect cannot be ignored when the sputtering is performed for a long time.
[0010]
In addition, a method for uniformly controlling the surface roughness of the sputtering target is known. If a target manufactured by this method is used, a stable film formation rate can be achieved with less abnormal discharge at the initial stage of sputtering. However, since the new surface appears from the middle stage to the latter stage of sputtering, nodules are likely to be generated on the target surface, and abnormal discharge occurs and stable film formation cannot be achieved.
[0011]
Incidentally, a transparent conductive thin film having a smooth surface and a low resistance is required for electrodes for LCD elements and organic EL elements. In particular, a transparent conductive thin film constituting an electrode of a display using an organic EL element is required to have excellent surface smoothness because an ultra thin film of an organic compound such as a light emitting layer is formed thereon.
[0012]
However, the surface smoothness of the transparent conductive thin film produced by the sputtering method increases the surface unevenness when a crystal phase is present in the film being deposited and grown. This is because the film undergoing deposition growth is irradiated with recoil argon particles and resputtering is also performed. That is, if a crystal phase is partially present in a film during deposition growth, the resputtering rate of the crystal phase is slower than that of the amorphous part, so that the crystal phase protrudes on the surface and becomes a film with severe surface irregularities.
[0013]
For example, even if sputtering is performed without heating the substrate, the kinetic energy of sputtering particles such as argon particles incident on the substrate is high, so the ITO film locally rises in temperature, resulting in a fine crystalline phase and an amorphous state. A mixed film of a quality phase will be formed. This tendency is more prominent as the sputtering gas pressure is lower. Such a fine crystal phase mixed in the amorphous phase can be easily confirmed not only by X-ray diffraction measurement but also by a transmission electron microscope.
[0014]
Furthermore, when forming a film for a display such as an LCD element or an organic EL element, there is a step of etching and removing the ITO film into a predetermined shape with a weak acid. However, the ITO film in which the fine crystal phase is partially formed together with the amorphous phase may remain without being able to remove only the crystal phase during the etching process, so that subsequent processing becomes a problem.
[0015]
On the other hand, if the entire film is an amorphous film during film formation, the film grows while being uniformly re-sputtered, so that a film with a smooth surface can be obtained. As a method for stably producing a completely amorphous ITO film, for example, there is a method for forming an amorphous ITO film by sputtering an ITO target at a low temperature of 100 to 120 ° C. (substrate temperature). It has been proposed (see Patent Document 2).
[0016]
However, the ITO film formed at such a low temperature can be easily patterned by wet etching because it is amorphous. However, the electrical resistivity increases and increases, and the visible light transmittance decreases. There is. This ITO film has the lowest specific resistance of 6 × 10^-4~ 8x10^-4In order to form an electrode for a display such as an LCD element or an organic EL element having a limit of Ω · cm and a lower surface resistance, the film must be made thick. However, when the ITO film is thicker than 500 nm, the problem of film coloring occurs.
[0017]
A method of forming an amorphous ITO film by introducing hydrogen gas into an inert gas for sputtering containing oxygen gas to form a film has also been proposed (see Patent Document 3). However, this method of forming a film by introducing hydrogen gas into the sputtering gas has a drawback that it is difficult to form an amorphous ITO film at a sufficient film formation rate.
[0018]
On the other hand, as a transparent conductive thin film that is amorphous and excellent in surface smoothness, In₂O₃-ZnO system is known (for example, refer to Patent Document 4). But this In₂O₃In the -ZnO-based thin film, metal Zn is contained as a component in the film, and thus the transmittance on the low wavelength side in the visible light region is inferior to that of the ITO thin film. In addition, metal Zn or ZnO contained in the film easily reacts with carbon dioxide gas or moisture in the air, so that the characteristics of the film are not stable and are insufficient for use as an electrode of an LCD element or an organic EL element.
[0019]
In recent years, attempts have been made to extract light emission from the cathode side using a transparent cathode for the EL element. If the cathode is made transparent together with the anode, a transparent element as a whole can be obtained. Further, if an arbitrary color is adopted as the background color of the transparent light emitting element, it is possible to make a colorful display other than during light emission, and the decorativeness is improved. When black is used as the background color, the contrast during light emission is improved. In the case of using a color filter or a color conversion layer, since these can be placed on the light emitting element, the element can be manufactured without considering these layers. Therefore, for example, there is an advantage that the substrate temperature can be increased during electrode formation, and thereby the resistance value of the electrode can be decreased.
[0020]
However, even in an EL element having these advantages, when a conventional ITO thin film is used as a transparent conductive thin film of an anode and / or a cathode, it is difficult to combine low resistance and surface smoothness.₂O₃As long as the —ZnO-based film is used, not only the transmittance on the low wavelength side in the visible light region is inferior to that of ITO, but also problems such as unstable characteristics remain. In addition, in order to smooth the surface of the transparent conductive thin film, it is possible to add a smoothing process such as etching or polishing after the film formation. However, the addition of a special process makes the process complicated and costly. Is also not preferred.
[0021]
As described above, in various display panels such as LCD elements and organic EL elements, which are becoming increasingly fine in recent years, the surface smoothness is excellent, the resistance is low, the transmittance is high, and the characteristics are stable. Conductive thin films are indispensable.
[0022]
[Patent Document 1]
JP 2000-144393 A
[Patent Document 2]
JP-A-4-48516
[Patent Document 3]
JP-A-3-64450
[Patent Document 4]
JP-A-6-234521
[0023]
[Problems to be solved by the invention]
In view of such conventional circumstances, the present invention includes a transparent conductive thin film having low resistance, excellent surface smoothness, large visible light transmittance, stable characteristics, a manufacturing method thereof, and the transparent conductive thin film. Another object of the present invention is to provide a transparent conductive substrate for a display panel and an EL element having excellent light emission characteristics.
[0024]
[Means for Solving the Problems]
As a result of examining the crystal structure, electrical characteristics, and optical characteristics of the transparent conductive thin films having various compositions formed by sputtering and the films crystallized by heating, the inventor has indium oxide as a main component. In addition, the transparent conductive thin film containing one or more of tungsten, silicon, and germanium can stably obtain a film having an amorphous structure excellent in surface smoothness, and can be crystallized by heating the amorphous film. 9 × 10 with the surface smoothness maintained.^-4It has been found that a low specific resistance of Ω · cm or less is obtained, and that it has a high visible light transmittance.
[0028]
That is, the method for producing a transparent conductive thin film provided by the present invention comprises indium oxide as a main component and is 0.2 to 0.2 with respect to the total amount of indium and the first additive element as the first additive element.15.2A method for producing on a substrate a crystalline transparent conductive thin film containing at least one selected from atomic% tungsten, silicon, and germanium, using a sputtering method, a vacuum deposition method, or an ion plating method, An inert gas containing oxygen is used as a film forming atmosphere, and after forming an amorphous thin film having the above composition without heating the base material, the thin film is formed in the atmosphere, in a vacuum, or an inert gas. Among these, heat treatment is performed at a temperature of crystallization temperature of the thin film to 700 ° C. to crystallize.
[0029]
MaAnd aboveProvided by the present inventionTransparent conductive thin filmThis manufacturing method may further contain tin as the second additive element in the transparent conductive thin film. The tin content is preferably 15 atomic% or less with respect to the total amount of indium and tin. Furthermore, the present invention provides,A transparent conductive thin film obtained by the method for producing a transparent conductive thin film described above,Any substrate selected from glass plate, quartz plate, resin plate, resin filmMaterialProvided is a transparent conductive substrate for a display panel having the above. It is preferable that at least one layer of an insulating layer, a semiconductor layer, a gas barrier layer, and a protective layer is formed on the substrate of the transparent conductive substrate for display panel.
[0030]
Furthermore, the present invention provides an electroluminescence device characterized by using the transparent conductive thin film described above for an anode and / or a cathode.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
The transparent conductive thin film of the present invention comprises indium oxide (In₂O₃) As a main component, and at least one of tungsten (W), silicon (Si), and germanium (Ge) as a first additive element is 0.2 to 0.2 in total with indium (In).15.2Contains atomic percent. In addition to the first additive element, tin can be further contained as the second additive element.
[0032]
The main features of the transparent conductive thin film of the present invention containing the above additive elements at a predetermined content are that the structure is crystalline and the surface roughness is 2.5 nm or less in terms of centerline average roughness (Ra). It is in. In the present invention, that the structure is crystalline means that when the crystallinity in the film is examined by X-ray diffraction measurement using CuKα rays, a diffraction peak caused by an indium oxide phase, for example, 2θ is 22 degrees, 31 degrees, It means that all or any one of diffraction peaks around 35 degrees, 37 degrees, 46 degrees, 52 degrees, and 56 degrees exists.
[0033]
The surface roughness of the transparent conductive thin film of the present invention is 2.5 nm or less in terms of centerline average roughness (Ra), and an extremely smooth thin film with Ra of 1.0 nm or less can be obtained by optimizing the film forming conditions. It is done. Here, the centerline average roughness (Ra) is measured with an atomic force microscope, specifically, the roughness is measured within an area of 1 μm × 1 μm for each of 10 arbitrary positions on the film surface. The average value is calculated. When Ra exceeds 2.5 nm, particularly when used as an electrode for an organic EL device, an ultra-thin film of an organic compound cannot be formed thereon. Therefore, a smoothing process such as etching or polishing is added after film formation. Will have to.
[0034]
About content of W, Si, and Ge which are 1st addition elements, it is 0.2 ~ with respect to the total amount with In.15.2By making it atomic%, it is easy to form an amorphous film with excellent surface smoothness when deposited by sputtering, vacuum deposition, or ion plating. The treatment can improve conductivity while maintaining excellent surface smoothness. When the content of the additive element is less than 0.2 atomic%, it is difficult for the film immediately after sputtering to have a completely amorphous structure. Even if crystallized, a film having excellent surface smoothness cannot be obtained. on the other hand,15.2If it exceeds atomic%, since there are too many additional elements, the specific resistance becomes too large, which is not preferable.
[0035]
The conductive mechanism of an ITO film, which is a conventional transparent conductive thin film, has been described as follows. That is, tin is likely to be a tetravalent ion, and when tetravalent tin is substituted and dissolved in the trivalent indium ion position of indium oxide, carrier electrons are emitted and the conductivity is improved. In addition, oxygen defects are easily generated in indium oxide, which also causes carrier electrons to be emitted, further improving conductivity.
[0036]
Therefore, in order to increase the carrier electron density of ITO, an appropriate amount of oxygen defects is required together with the addition of tin. However, since the mobility of carrier electrons decreases as the number of oxygen defects increases, in order to minimize the electrical resistivity, a tetravalent valence is easily obtained as in the case of tin. It is conceivable to employ an element that emits electrons as a dopant.
[0037]
In the present invention, the first additive element tungsten, silicon, germanium, and the second additive element tin are easy to have a tetravalent valence, and when substituted at the indium position of indium oxide, the element emits carrier electrons. It is thought that this also acts to reduce the specific resistance of the transparent conductive thin film.
[0038]
Therefore, the specific resistance of the transparent conductive thin film in the present invention is 9.0 × 10^-4It is possible to provide an electrode film having a low surface resistance that is Ω · cm or less and is suitable as a transparent electrode for LCD elements and organic EL elements. Preferred specific resistance is 6.0 × 10^-4Ω · cm or less, 3 × 10 if the film formation conditions are optimized^-4It is also possible to set it to Ω · cm or less. Specific resistance is 9.0 × 10^-4If it exceeds Ω · cm, it is necessary to form a thick film in order to obtain a desired surface resistance. As a result, the film is colored, which is not preferable. Note that the specific resistance of the conventional amorphous ITO film is 6 × 10, even if the conditions are optimized using a special film formation method as described in Patent Document 2 or Patent Document 3.^-4~ 8x10^-4Ω · cm was the limit.
[0039]
Moreover, in the transparent conductive thin film of this invention, in addition to the said 1st addition element, tin (Sn) can further be contained as a 2nd addition element. By containing Sn, the conductivity of the transparent conductive thin film can be further improved. The content of Sn is 15 atomic% or less with respect to the total amount of Sn and In, and is preferably in the range of 0.5 to 15 atomic%. If the content exceeds 15 atomic%, the specific resistance becomes too large, which is not preferable. In the transparent conductive thin film of the present invention, elements other than the first additive element and the second additive element, such as Ag, Cu, Au, Pt, Pd, Ir, Re, Os, Ru, Ti, Mo, Hf, An element such as Ce may be contained within a range not impairing the object of the present invention.
[0040]
Furthermore, the transparent conductive thin film of the present invention has an average visible light transmittance at a wavelength of 400 to 800 nm of 85% or more, preferably 88% or more, and more preferably 90% or more. When the average visible light transmittance is less than 85%, application to an organic EL element or the like becomes difficult.
[0041]
Next, the manufacturing method of the transparent conductive thin film of this invention is demonstrated. The method for producing a transparent conductive thin film of the present invention comprises two steps: a first step for forming an amorphous film with excellent surface smoothness and a second step for crystallizing the amorphous film by heat treatment. Has been. The inventor has already filed patent applications for the amorphous film formation method related to the first step (Japanese Patent Application Nos. 2002-330058, 2002-337130 and 2002-353011). reference).
[0042]
First, in the first step of forming the amorphous film, the main component is indium oxide, and the first additive element is 0.2 to 0.2% relative to the total amount of indium and the first additive element.15.2A composition containing at least one selected from tungsten, silicon, and germanium of atomic percent, and optionally containing 15 atomic percent or less of tin as a second additive element with respect to the total amount of indium and tin, and A substantially amorphous thin film is formed. As a film forming method, a sputtering method, particularly a direct current magnetron sputtering method is preferable, but a vacuum vapor deposition method or an ion plating method can also be used. In addition, the composition of a sputtering target or evaporation source as a film forming material is adjusted according to the film composition to be formed.
[0043]
As the film formation atmosphere, an inert gas such as argon containing oxygen is used. The oxygen gas needs to be mixed at 1% or more, preferably 1 to 5%. If the oxygen gas is less than 1%, the transparency of the resulting film is low, and the dopant tends to be detached from the surface of the film, so that compositional deviation tends to occur. On the other hand, if the oxygen gas exceeds 5%, the resistance value of the film increases, which is not preferable. The pressure of the atmospheric gas is preferably 0.1 to 1 Pa. If the pressure is less than 0.1 Pa, the film is difficult to become amorphous, and if it exceeds 1 Pa, a dense film cannot be obtained. In particular, an amorphous film is easily formed in the range of 0.3 to 0.8 Pa, and the surface smoothness can be improved.
[0044]
In this first step, an amorphous film having excellent surface smoothness can be formed without heating the substrate, but depending on the film composition, the amorphous film can also be formed by heating the substrate to 100 to 200 ° C. A quality film can be obtained. This effect is obtained when silicon or germanium is added as the first additive element, but is more remarkable when tungsten is further added in addition to silicon or germanium.
[0045]
In the first step, since the indium oxide to which the first additive element such as silicon, germanium, tungsten or the like is added is used as a film forming material, the crystallization temperature of the material itself is higher than that of the conventional ITO. Even if the temperature rises locally in the film due to the kinetic energy, it is considered that it is difficult to crystallize and a film having an amorphous structure can be stably obtained.
[0046]
That is, Si⁴⁺Has an ionic radius of 0.39 Å and Ge⁴⁺Has an ion radius of 0.53 Å, both of which are In³⁺Therefore, when silicon or germanium is added to indium oxide, the lattice is easily distorted, and the indium oxide structure cannot be maintained and the crystallization temperature rises. In addition, when tungsten is contained in indium oxide, the covalent bond between In—O is increased, and the amorphous structure can be further stabilized. In addition, the specific resistance of the obtained amorphous film is reduced by the addition of tungsten.
[0047]
The present inventor has confirmed that when tungsten is contained in indium oxide, the covalent bond between In—O is increased by calculating material physical properties by a molecular orbital calculation method by the DV-Xα method. When the covalent bond between In-O increased, it was speculated that the crystallization temperature increased, and it could be confirmed by experiments. That is, In₂O₃The crystallization temperature of the film is about 150 ° C., but it became clear from the high temperature X-ray diffraction measurement of the film that the crystallization temperature rises to about 200 ° C. when only 0.6 atomic% of tungsten is contained. . Therefore, an amorphous film having a smooth surface can be stably obtained by using a film composition containing tungsten in particular.
[0048]
In the conventional ITO, in order to obtain an amorphous film, it was necessary to perform sputtering under a high gas pressure so that the energy of the sputtered particles is reduced without heating the substrate. However, in the case of indium oxide to which the first additive element such as tungsten or silicon is added as in the present invention, it is easy to obtain a completely amorphous film even if the gas pressure is low, for example. That is, since the crystallization temperature increases as the amount of the first additive element in the film increases, the crystallization corresponding to the film composition can be achieved even if the substrate temperature is substantially increased by sputtering or the substrate is heated. If the temperature is lower than the temperature, the formed film has an amorphous structure.
[0049]
Following the formation of the amorphous film in the first step, the amorphous film is crystallized in the second step. That is, the amorphous transparent conductive thin film excellent in surface smoothness obtained in the first step is crystallized while maintaining excellent surface smoothness by heat treatment at a temperature higher than the crystallization temperature. At the same time, the specific resistance can be reduced. Further, since the surface of the obtained crystalline transparent conductive thin film is sufficiently smooth, there is no need to add a smoothing process such as etching or polishing later.
[0050]
The heating temperature may be a temperature equal to or higher than the crystallization temperature, but is preferably 700 ° C. or lower, and more preferably 500 ° C. or lower. This is because when the heating temperature exceeds 700 ° C., crystal growth occurs, crystal grains are uneven, and surface smoothness is impaired. The crystallization temperature depends on the type and amount of additive element in indium oxide. In addition, the heating atmosphere may be a vacuum, an inert gas atmosphere such as argon or nitrogen, or an atmosphere containing oxygen.
[0051]
When crystallization is performed by heat treatment, the ratio of the first additive element such as tungsten, silicon, germanium, and the like that is substituted and dissolved in the indium sites of indium oxide increases, the number of carrier electrons increases, and the Burstein-Moss shift. The effect ("Transparent conductive film technology", edited by Japan Society for the Promotion of Science, published by Ohm, p. 73) widens the apparent band gap and increases the transmittance on the short wavelength side in the visible light region. In this way, the transparent conductive thin film according to the present invention is obtained which is crystalline, excellent in surface smoothness, low resistance, and high visible light transmittance comparable to that of ITO.
[0052]
The transparent conductive substrate for display panel of the present invention is any one selected from a glass transparent plate, a quartz plate, a resin plate, or a resin film as a crystalline transparent conductive thin film having excellent surface smoothness and low resistance. It is formed on such a base material. The display panel is an LCD element, a PDP element, an EL element, or the like, and includes a transparent conductive thin film as its anode and / or cathode.
[0053]
The base material that supports the transparent conductive thin film base material needs to have a certain strength and transparency. Examples of the material constituting the resin plate or the resin film include polyethylene terephthalate (PET), polyether sulfone (PES), polyarylate (PAR), polycarbonate (PC), etc., and these surfaces are coated with acrylic resin. It may be of a structured. Moreover, as a resin board or a resin film, it is desirable to use what has a glass transition point higher than the crystallization temperature of a transparent conductive thin film.
[0054]
Although the thickness of a base material is not necessarily limited, 0.5-10 mm is preferable in a glass plate or a quartz plate, and 1-5 mm is still more preferable. Moreover, in the case of a resin plate or a resin film, 0.1-5 mm is preferable and 1-3 mm is still more preferable. A substrate thicker than this range is not only poor in transparency, but also increases in weight and strength, and is difficult to handle.
[0055]
Any of an insulating layer, a semiconductor layer, a gas barrier layer, and a protective layer can be formed in advance on the surface of the substrate. As the insulating layer, a silicon oxide (Si—O) film, a silicon nitride oxide (Si—O—N) film, or the like can be given. As the semiconductor layer, there is a thin film transistor (TFT) or the like, which is mainly formed on a glass substrate. The gas barrier layer is formed on a resin plate or a resin film as a water vapor barrier film or the like. The protective layer is for protecting the surface of the substrate from scratches and impacts, and various coatings such as silicon-based, titanium-based, and acrylic resin-based are used. Note that the layers that can be formed in advance on the surface of the substrate are not limited to these, and a thin conductive metal film or the like may be provided.
[0056]
Such a transparent conductive substrate for a display panel according to the present invention includes a crystalline transparent conductive thin film having excellent characteristics such as specific resistance, light transmittance, and surface flatness. It is extremely useful as a component part.
[0057]
Moreover, the EL element of the present invention uses the above-described crystalline transparent conductive thin film excellent in surface smoothness and low resistance as an anode and / or a cathode. Among the EL elements, the basic structure of the organic EL element to which the present invention is most effectively applied is between the anode and the cathode by recombination of holes supplied from the anode and electrons supplied from the cathode. An organic layer including a light emitting layer that emits light is provided.
[0058]
An example of such an organic EL element is shown in FIG. As the anode 2, the transparent conductive thin film of the present invention is suitable. The organic layer 6 between the anode 2 and the cathode 3 may be only the light emitting layer 7 that emits light by recombination of the holes supplied from the anode 2 and the electrons supplied from the cathode 3, but further the holes A multilayer structure in which the injection layer 8 and the hole transport layer 9 are laminated may be used. The cathode 3 includes a conductive thin layer 4 and a metal layer 5. A protective film 11 is provided on the conductive thin layer 4 of the cathode 3, and an insulating layer 10 is provided on the insulating substrate 1.
[0059]
The organic layer 6 between the anode 2 and the cathode 3 has (1) a function capable of injecting holes from the anode 2 side and electrons from the cathode 3 side when an electric field is applied, and (2) injected charges (electrons and positive ions). And (3) a light emitting function for providing a field for recombination of electrons and holes inside the light emitting layer 7 and connecting it to light emission. The hole injection layer 8 and the hole transport layer 9 are layers made of a hole transfer compound, and have a function of transmitting holes injected from the anode 2 to the light emitting layer 7. By interposing the hole injection layer 8 and the hole transport layer 9 between the anode 2 and the light emitting layer 7, many holes can be injected into the light emitting layer 7 with a lower electric field.
[0060]
In general, the anode 2 is preferably a metal having a work function of 4.4 eV or more, preferably 4.8 eV or more, a transparent conductive film, or a laminate thereof. The metal exhibiting conductivity is not necessarily transparent, and may be coated with a black carbon layer or the like. Examples of suitable metals include Au, Pt, Ni, Pd, Cr, and W. As the material of the transparent conductive film, the surface-smooth crystalline transparent conductive thin film of the present invention, that is, In—W—O, In—Si—O, In—Ge—O, In—Si—Sn—O, In The use of —Si—W—O, In—Si—Sn—W—O, In—Ge—Sn—O, In—Ge—W—O, In—Ge—Sn—W—O, etc. is effective. Moreover, as a laminated body of a transparent conductive film and a metal, for example, a laminated body of a surface-smooth crystalline transparent conductive thin film of the present invention such as the above-described In—W—O system and Au or Pt can be cited. be able to.
[0061]
Further, since the anode 2 only needs to have a work function of 4.4 eV or more at the interface with the organic layer 6, the anode has a two-layer structure, and a transparent conductive film having a work function of 4.4 eV or less on the side not in contact with the organic layer 6. May be used. Further, on the side not in contact with the organic layer 6, a metal such as Al, Ta, or Nb, an alloy such as an Al alloy or Ta-W alloy, a conductive polymer such as doped polyaniline or doped polyphenylene vinylene, a Amorphous semiconductors such as -Si, a-SiC, and a-C can also be used. Furthermore, Cr is a black semiconductive oxide.₂O₃, Pr₂O₅, NiO, Mn₂O₅, MnO₂Etc. can also be used.
[0062]
On the other hand, the cathode 3 may basically be composed of the metal thin film 5, but may also have a two-layer structure (laminated body) of the conductive thin film 4 and the metal thin film 5 as shown in the figure. The metal thin film 5 constituting the cathode 3 is a layer for favorably injecting electrons into the organic layer 6 including the light emitting layer 7. The electrons injected into the light emitting layer 7 from the cathode 3 side are accumulated near the interface in the light emitting layer 7 due to an electron barrier existing at the interface between the light emitting layer 7 and the hole transport layer 9, and the light emission efficiency of the organic EL element. To improve.
[0063]
In order to obtain a transparent organic EL element, the light transmittance of the metal thin film 5 is preferably 50% or more, and more preferably 60% or more. In that case, it is desirable that the metal thin film 5 has a thickness of about 0.5 to 20 nm. The metal thin film 5 is preferably a metal having a work function of 3.8 eV or less, such as Mg, Ca, Ba, Sr, Yb, Eu, Y, Sc, Li, or an alloy thereof. Moreover, also in the case of the cathode 3 which consists of a laminated body of this metal thin film 5 and the transparent conductive thin film 4, a transparent organic EL element can be formed.
[0064]
In the case of a transparent organic EL element or an organic EL element that emits light to the substrate side, a transparent insulating substrate 1 is used. As the transparent insulating substrate 1, a glass plate, a quartz plate, or a resin plate can be used. However, a resin film or a barrier film covered with a water vapor barrier film such as a silicon oxide film or a silicon nitride oxide film is provided. A resin film is preferred.
[0065]
The organic EL device of the present invention uses a crystalline transparent conductive thin film having high visible light transmittance, low resistance and excellent surface smoothness as an anode and / or a cathode conductive thin film. Compared with the case of using a transparent conductive thin film such as a conventional ITO, the average light emission luminance in the initial stage is large and the luminance half-life is long.
[0066]
【Example】
Example 1
99.99% pure In₂O₃Powder and WO₃The powder was mixed in a ball mill, pressed, and then heated and sintered at 1400 ° C. to produce an indium oxide sintered body containing tungsten. After processing this sintered body to a diameter of 6 inches and a thickness of 5 mm, it was bonded to a backing plate made of oxygen-free copper using an In-based alloy, and W containing In₂O₃Targeted.
[0067]
This sputtering target was attached to a nonmagnetic target cathode of a DC magnetron sputtering apparatus, and a synthetic quartz glass substrate having a size of 50 mm × 50 mm × 1.0 mm in thickness was attached to the opposing surface of the target. The distance between the target and the substrate is 70 mm, the inside of the chamber is evacuated, and the degree of vacuum is 1 × 10^-4When the pressure reached Pa or lower, Ar gas having a purity of 99.9999% by weight was introduced to set the gas pressure in the chamber to 0.6 Pa, and oxygen was further introduced by 1 to 3%. With the substrate held at room temperature, DC power of 100 to 200 W was applied between the target and the substrate, DC plasma was generated and sputtering was performed, and a transparent conductive thin film having a thickness of about 100 to 300 nm was formed. .
[0068]
WO at the time of target production₃By changing the amount of powder and changing the composition of the sputtering target, transparent conductive thin films made of indium oxide having various tungsten contents were prepared. The crystallinity of each transparent conductive thin film thus produced was examined by X-ray diffraction measurement using CuKα rays. As a result, it was an amorphous structure containing no crystal phase. Further, as a result of examining the surface smoothness of the film with an atomic force microscope, it was confirmed that the film was very flat.
[0069]
Next, these amorphous transparent conductive thin films were crystallized by heat treatment at 300 to 350 ° C. for 10 minutes in a nitrogen gas atmosphere. Crystallization of the film was confirmed by X-ray diffraction measurement using a CuKα ray, a transmission electron microscope, and electron diffraction. For example, in the X-ray diffraction pattern, there are peaks at 2θ of around 22 degrees, 31 degrees, 35 degrees, 37 degrees, 46 degrees, 52 degrees, and 56 degrees. It was confirmed that
[0070]
The specific resistance and visible light transmittance of the crystallized transparent conductive thin film depended on the amount of oxygen gas mixed at the time of sputtering, but the specific resistance in the film having visible light transmittance of 80% or more and the same tungsten content. The film having the lowest value was evaluated by measuring the composition analysis, specific resistance, and surface roughness of the film by the following methods.
(1) The composition of the transparent conductive thin film was measured by ICP emission analysis on a film produced by changing the substrate from glass to silicon wafer (purity 99.99%) and using the same other film forming conditions.
(2) The specific resistance of the transparent conductive thin film was measured by a four-point probe method.
(3) The light transmittance of the transparent conductive thin film was measured with a spectrophotometer (manufactured by Hitachi, Ltd.).
(4) The center line average roughness (Ra) of the surface of the transparent conductive thin film was measured with an atomic force microscope (NSIII, D5000 system manufactured by Digital Instruments). Note that Ra was measured in an area of 1 μm × 1 μm for each of 10 arbitrary positions on the film surface, and the average value was calculated.
[0071]
For each crystalline transparent conductive thin film made of indium oxide containing tungsten according to the present invention, the heating measured as described above for each sample having a different tungsten content (atomic% with respect to the total amount of tungsten and indium) in the film The specific resistance and centerline average roughness (Ra) of the crystalline film after the treatment are shown in Table 1 below.
[0072]
[Table 1]

[0073]
As is apparent from Table 1, the crystalline transparent conductive thin films of samples 1 to 8 made of indium oxide containing tungsten according to the present invention all have a specific resistance of 8.8 × 10 6.^-4Ωcm or less, mostly 6.0 × 10^-4It was as low as Ωcm or less. In each of the amorphous transparent conductive thin films before heat treatment of Samples 1 to 8, the specific resistance is 4.1 to 9.5 × 10.^-4Although it was Ωcm, it can be seen that the specific resistance decreased due to crystallization by heat treatment. For example, in Sample 5 having a tungsten content of 5.6 atomic%, the specific resistance of the amorphous film before the heat treatment is 4.8 × 10 6.^-4Whereas it is Ωcm, the crystalline film after heat treatment is 3.6 × 10^-4It decreased to Ωcm.
[0074]
Further, it was found that the surface roughness of the film surface in all the samples of the present invention was 2.1 nm or less in terms of the average value of the center line average roughness Ra and was very smooth. In addition, even in each amorphous transparent conductive thin film before heat treatment, Ra is very smooth as 1.4 to 2.0 nm, and excellent surface smoothness is maintained even after crystallization by heat treatment. You can see that it is. Furthermore, the average visible light transmittance of the film was 85 to 94%, and the transmittance was also good. The light transmittance of the film itself at a wavelength of 400 nm increased by 10 to 30% by heating, and the transmittance on the short wavelength side was improved as compared with the amorphous film before heating.
[0075]
In the above embodiment, the heat treatment for crystallization was performed in a nitrogen atmosphere. However, even if the heat treatment for crystallization is performed in another inert gas such as argon, in a vacuum or in the atmosphere, Similar results were obtained.
[0076]
Example 2
In₂O₃Powder and WO₃Powder and SiO₂An indium oxide sintered body target containing tungsten and silicon was produced in the same manner as in Example 1 except that powder was used. Further, a direct current magnetron sputtering method using this target was used to form a film under the same conditions as in Example 1 to produce a transparent conductive film made of indium oxide containing tungsten and silicon.
[0077]
It was confirmed by X-ray diffraction measurement that the transparent conductive thin film thus produced was amorphous. The various transparent conductive thin films made of indium oxide having different contents of tungsten and silicon were subjected to a heat treatment at 300 to 450 ° C. for 10 minutes in the air to produce a crystalline transparent conductive thin film. It was confirmed by X-ray diffraction measurement as in Example 1 that the film was crystallized.
[0077]
For each of the obtained crystalline transparent conductive thin films made of indium oxide containing tungsten and silicon according to the present invention, the tungsten content and the silicon content (both of the contents of tungsten, silicon, and indium are the same as in Example 1). Atomic% relative to the total), specific resistance and centerline average roughness (Ra) were measured, and the results are shown in Table 2 below. The substrate used for the composition analysis was a silicon wafer in Example 1, but here, a germanium wafer (purity 99.99%) was used.
[0078]
[Table 2]

[0079]
As is apparent from Table 2 above, all of the crystalline transparent conductive thin films of Samples 9 to 20 made of indium oxide containing tungsten and silicon according to the present invention have a specific resistance of 8.6 × 10 6.^-4The resistivity was as low as Ω · cm or less, and the specific resistance was lower than that of the amorphous film before the heat treatment. In all samples, the average value of the center line average roughness Ra on the surface of the film was very smooth, 2.2 or less, and the amorphous film Ra 1.1 to 1.9 nm before heat treatment was excellent. It was found that the smoothness was maintained. Furthermore, the average visible light transmittance of the film was 85 to 93%, and the transmittance was also good. The light transmittance of the film itself at a wavelength of 400 nm increased by 10 to 30% by heating, and the transmittance on the short wavelength side was improved as compared with the amorphous film before heating.
[0080]
In the above embodiment, the heat treatment for crystallization is performed in the atmosphere. However, the same heat treatment for crystallization may be performed in vacuum or in an inert gas such as argon or nitrogen. Results were obtained.
[0081]
Example 3
In₂O₃Powder and WO₃Powder and GeO₂An indium oxide sintered compact target containing tungsten and germanium was produced in the same manner as in Example 1 except that powder was used. Further, a direct current magnetron sputtering method using this target was used to form a film under the same conditions as in Example 1 to produce a transparent conductive film made of indium oxide containing tungsten and germanium.
[0082]
It was confirmed by X-ray diffraction measurement that the transparent conductive thin film thus produced was amorphous. Various transparent conductive thin films made of indium oxide having different contents of tungsten and germanium were subjected to heat treatment at 300 to 450 ° C. for 10 minutes in the air to produce crystalline transparent conductive thin films. It was confirmed by X-ray diffraction measurement as in Example 1 that the film was crystallized.
[0083]
For each of the crystalline transparent conductive thin films made of indium oxide containing tungsten and germanium of the present invention, the tungsten content and the germanium content (both of the contents of tungsten, germanium and indium are the same as in Example 1). Atomic% relative to the total), specific resistance and centerline average roughness (Ra) were measured, and the results are shown in Table 3 below. The substrate used for the composition analysis was a germanium wafer (purity 99.99%).
[0084]
[Table 3]

[0085]
As is clear from Table 3, the crystalline transparent conductive thin films of Samples 21 to 32 made of indium oxide containing tungsten and germanium of the present invention all have a specific resistance of 8.7 × 10.^-4Ω · cm or less, mostly 6.0 × 10^-4The resistivity was lower than Ωcm, and the specific resistance was lower than that of the amorphous film before the heat treatment. In all samples, the average value of the center line average roughness Ra on the film surface was as smooth as 1.9 or less, and it was excellent that the amorphous film had a Ra of 0.7 to 1.7 nm before the heat treatment. It can be seen that the smoothness is maintained. Furthermore, the average visible light transmittance of the film was 85 to 93%, and the transmittance was also good. The light transmittance of the film itself at a wavelength of 400 nm increased by 10 to 30% by heating, and the transmittance on the short wavelength side was improved as compared with the amorphous film before heating.
[0086]
In the above embodiment, the heat treatment for crystallization is performed in the atmosphere. However, the same heat treatment for crystallization may be performed in vacuum or in an inert gas such as argon or nitrogen. Results were obtained.
[0087]
Example 4
In₂O₃Powder and WO₃Powder and SiO₂Powder or GeO₂Powder and SnO₂An indium oxide sintered compact target containing tungsten, silicon, germanium, or tin was produced in the same manner as in Example 1 except that powder was used. In addition, a direct current magnetron sputtering method using this target was used to form a film under the same conditions as in Example 1 to produce a transparent conductive film made of indium oxide containing tungsten, silicon, germanium, or tin.
[0088]
It was confirmed by X-ray diffraction measurement that the transparent conductive thin film thus produced was amorphous. Various transparent conductive thin films made of tungsten, silicon or germanium, and indium oxide having different tin contents are subjected to a heat treatment at 300 to 450 ° C. for 10 minutes in the atmosphere, thereby producing a crystalline transparent conductive thin film Was made. It was confirmed by X-ray diffraction measurement as in Example 1 that the film was crystallized.
[0089]
For each of the crystalline transparent conductive thin films made of tungsten of the present invention, silicon or germanium, and indium oxide containing tin, as in Example 1, the tungsten content and the silicon or germanium content (both Atomic% relative to the total of tungsten, germanium, and indium), tin content (atomic% relative to the total of tin and indium), specific resistance, and centerline average roughness (Ra) were measured, and the results are shown in Table 4 below. It was. The substrate used for the composition analysis was a germanium wafer as the substrate when silicon was included in the film, and a silicon wafer was used as the substrate when germanium was included in the film.
[0090]
[Table 4]

[0091]
As is apparent from Table 4, the crystalline transparent conductive thin films of Samples 33 to 40 made of indium oxide containing tungsten, silicon or germanium, and tin according to the present invention all have a specific resistance of 6.7 × 10 6.^-4The resistivity was as low as Ω · cm or less, and the specific resistance was lower than that of the amorphous film before the heat treatment. In all samples, the average value of the center line average roughness Ra on the film surface was very smooth at 1.9 or less, and the amorphous film Ra 0.9 to 1.5 nm before heat treatment was excellent. It was found that smoothness was maintained. Furthermore, the average visible light transmittance of the film was 85 to 90%, and the transmittance was also good. The light transmittance of the film itself at a wavelength of 400 nm increased by 10 to 30% by heating, and the transmittance on the short wavelength side was improved as compared with the amorphous film before heating.
[0092]
In the above embodiment, the heat treatment for crystallization is performed in the atmosphere. However, the same heat treatment for crystallization may be performed in vacuum or in an inert gas such as argon or nitrogen. Results were obtained.
[0093]
In each of the transparent conductive thin films of the present invention shown in Examples 1 to 4 above, the amorphous film before crystallization treatment by heating was etched using a weakly acidic etchant. The etching characteristics were good because the speed was high and there was no part where the etching was shallow. After that, the etched amorphous film was crystallized by heat treatment under the same conditions as in each example, and the characteristics such as surface smoothness, specific resistance, and visible light transmittance of the film were etched. The results were almost the same as those of Examples 1 to 4 evaluated.
[0094]
Comparative Example 1
Using an indium oxide (ITO) sintered body target containing tin that has been widely used in the past, an amorphous thin film having a film thickness of about 100 to 300 nm was formed by a sputtering method with the substrate temperature at room temperature. . The gas composition and gas pressure during sputtering, the distance between the target and the substrate, the target size, and the like were performed under the same conditions as in Example 1.
[0095]
The obtained ITO thin film was confirmed by X-ray diffraction measurement, transmission electron microscope and electron beam diffraction. As a result, it was found that an amorphous portion and a crystalline portion were mixed. Further, the center line average roughness (Ra) of this ITO thin film was 4.5 to 6.6 nm, and the surface unevenness was very large. The amorphous ITO thin film was crystallized by performing a heat treatment at 300 to 400 ° C. in nitrogen gas. It was confirmed by X-ray diffraction measurement as in Example 1 that the film was crystallized.
[0096]
About the crystalline transparent conductive thin film made of indium oxide (ITO) containing tin obtained, as in Example 1, the tin content (atomic% with respect to the sum of tin and indium), specific resistance, and center line average roughness The thickness (Ra) was measured, and the results are shown in Table 5 below.
[0097]
[Table 5]

[0098]
As shown in Table 5, the ITO thin films of Samples 41 to 46, which are comparative examples, all have a specific resistance of 2.5 × 10.^-4~ 6.6 × 10^-4The average visible light transmittance of the film was 85 to 90%, and the transmittance was also good. However, it can be seen that the center line average roughness (Ra) of the film is 4.8 to 6.6 nm, which is significantly larger than the films shown in Examples 1 to 4 of the present invention. In these comparative examples, it is considered that large surface irregularities in the ITO thin film before the heat treatment are crystallized as it is by the heat treatment.
[0099]
Therefore, in order to use the ITO film of these comparative examples as a transparent electrode of an LCD element or an organic EL element, it is necessary to remove the surface irregularities by performing etching or polishing on the surface later.
[0100]
Further, when the etching characteristics of the ITO film before heating were examined using a weakly acidic etchant, it was found that a shallow etched portion was likely to occur in the crystal phase portion. Also, the etching rate was slow, and the etching time was 1.5 to 2 times that of the films of Examples 1 to 4 described above. In addition, it turned out that the ITO thin film obtained by heat-processing after an etching process remains etching shallow, and cannot be used as a transparent electrode for a display.
[0101]
Comparative Example 2
Conventionally used In₂O₃A transparent conductive thin film made of indium oxide containing zinc was produced under the same conditions as in Example 1 using a sintered body target of -ZnO (10 wt%).
[0102]
In obtained₂O₃The —ZnO thin film had an amorphous structure, the center line average roughness (Ra) of the film surface was 1.2 to 1.8 nm, and the surface smoothness was good. The specific resistance of the film is also 5.1 × 10^-4The value was as low as Ωcm.
[0103]
However, the light transmittance of the film itself in the vicinity of a wavelength of 400 nm was 25%, which was clearly inferior to the transparent conductive thin films (73%) of Examples 1 to 4. This In₂O₃When the -ZnO thin film was analyzed by XPS, it was found that the film contained metal Zn, and it was determined that this caused a decrease in light transmittance at a wavelength of around 400 nm.
[0104]
This In₂O₃-The ZnO thin film was crystallized by heating at 300-400 degreeC for 10 minutes in nitrogen gas. However, the crystallized thin film slightly improved the transmittance around the wavelength of 400 nm, but did not reach the transparent conductive thin films of Examples 1 to 4 of the present invention.
[0105]
In Examples 1 to 4 and Comparative Examples 1 and 2 described above, the sputtering method was used to form the amorphous film in the first step, but the film was formed by vacuum deposition and ion plating. The same result was obtained.
[0106]
【The invention's effect】
According to the present invention, it is possible to provide a transparent conductive thin film that is crystalline, has high visible light transmittance, low resistance, and at the same time has excellent surface smoothness, and a method for producing the same. This transparent conductive thin film is extremely useful as a transparent electrode for display device elements such as inorganic EL elements and LCDs as well as organic EL elements that require a smooth surface and a low resistance electrode.
[0107]
Therefore, the organic EL device using the transparent conductive thin film of the present invention as an electrode has higher emission luminance than before and has a longer half-life of the luminance, no dark spots, and excellent durability. And its industrial value is extremely high.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a specific example of an organic EL device of the present invention.
[Explanation of symbols]
1 Insulating substrate
2 Anode
3 Cathode
4 Conductive thin film
5 Metal thin film
6 Organic layer
7 Light emitting layer
8 Hole injection layer
9 Hole transport layer
10 Insulating layer
11 Protective film

Claims (11)

A crystal containing indium oxide as a main component and at least one selected from 0.2 to 15.2 atomic% of tungsten, silicon, and germanium with respect to the total amount of indium and the first additive element as the first additive element A transparent transparent conductive thin film on a substrate, using a sputtering method, a vacuum deposition method or an ion plating method, and heating the substrate using an inert gas containing oxygen as a film forming atmosphere Without forming an amorphous thin film having the above composition, the thin film is heat-treated at a temperature not lower than the crystallization temperature of the thin film and not higher than 700 ° C. in the air, in a vacuum, or in an inert gas. And then crystallizing the transparent conductive thin film. Further comprising a tin, and the content of tin is 15 atomic% or less of the total amount of indium and tin transparent conductive thin film of the crystalline as the second additional element, in claim 1 The manufacturing method of the transparent conductive thin film of description. 2. The transparent conductive thin film obtained by the method for producing a transparent conductive thin film according to claim 1, wherein the content of tungsten as the first additive element is 0.2 with respect to the total amount of indium and the first additive element. ~ 14.8 atomic%, specific resistance is 8.8 × 10 ^-4 A transparent conductive thin film having a surface roughness of 2.1 nm or less in terms of center line average roughness (Ra) of Ω · cm or less. The transparent conductive thin film obtained by the method for producing a transparent conductive thin film according to claim 1, wherein the content of tungsten and silicon as the first additive element is 0 with respect to the total amount of indium and the first additive element. 0.5 to 15.2 atomic%, specific resistance is 8.6 × 10 ^-4 A transparent conductive thin film having a surface roughness of 2.2 nm or less in terms of centerline average roughness (Ra) of Ω · cm or less. 2. The transparent conductive thin film obtained by the method for producing a transparent conductive thin film according to claim 1, wherein the content of tungsten and germanium as the first additive element is 0 with respect to the total amount of indium and the first additive element. 0.8 to 13.0 atomic%, specific resistance is 8.7 × 10 ^-4 A transparent conductive thin film having a surface roughness of 1.9 nm or less in terms of center line average roughness (Ra) of Ω · cm or less. 3. The transparent conductive thin film obtained by the method for producing a transparent conductive thin film according to claim 2, wherein the content of tungsten and silicon as the first additive element is 2 with respect to the total amount of indium and the first additive element. 0.3 to 6.0 atomic%, the tin content is 3.2 atomic% or less with respect to the total amount of indium and tin, and the specific resistance is 6.6 × 10 6 ^-4 A transparent conductive thin film having a surface roughness of 1.9 nm or less in terms of center line average roughness (Ra) of Ω · cm or less. 3. The transparent conductive thin film obtained by the method for producing a transparent conductive thin film according to claim 2, wherein the content of tungsten and germanium as the first additive element is 1 with respect to the total amount of indium and the first additive element. 0.5 to 9.2 atomic%, the tin content is 5.4 atomic% or less with respect to the total amount of indium and tin, and the specific resistance is 6.7 × 10 6 ^-4 A transparent conductive thin film having a surface roughness of not more than Ω · cm and a surface roughness of 1.7 nm or less in terms of centerline average roughness (Ra). The transparent conductive thin film according to any one of claims 3 to 7, wherein an average visible light transmittance is 85% or more. A transparent conductive thin film for a display panel, comprising the transparent conductive thin film according to claim 3 on a substrate selected from a glass plate, a quartz plate, a resin plate, and a resin film. Base material. The transparent conductive substrate for a display panel according to claim 9 , wherein at least one layer of an insulating layer, a semiconductor layer, a gas barrier layer, and a protective layer is formed on the substrate. An electroluminescent device using the transparent conductive thin film according to claim 3 for an anode and / or a cathode.

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