JP6294842B2 - Method for producing Eu-doped ZnO transparent conductive film - Google Patents

Method for producing Eu-doped ZnO transparent conductive film Download PDF

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JP6294842B2
JP6294842B2 JP2015011480A JP2015011480A JP6294842B2 JP 6294842 B2 JP6294842 B2 JP 6294842B2 JP 2015011480 A JP2015011480 A JP 2015011480A JP 2015011480 A JP2015011480 A JP 2015011480A JP 6294842 B2 JP6294842 B2 JP 6294842B2
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赤澤　方省
方省 赤澤
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本発明は、ＥｕドープＺｎＯ透明導電膜及びその形成方法に関する。   The present invention relates to a Eu-doped ZnO transparent conductive film and a method for forming the same.

透明導電膜は透明電極として産業的に利用されている。フラットパネルディスプレイの透明電極としては、現在ＩＴＯが独占的に用いられているが、Ｉｎ資源の枯渇の問題から代替材料が探索されている。これまでのところ、ＡｌドープＺｎＯやＧａドープＺｎＯといったＺｎＯ系透明導電膜が代替材料の有力候補に挙げられている。   Transparent conductive films are industrially used as transparent electrodes. Currently, ITO is used exclusively as a transparent electrode for flat panel displays, but alternative materials are being searched for due to the problem of depletion of In resources. So far, ZnO-based transparent conductive films such as Al-doped ZnO and Ga-doped ZnO have been cited as promising candidates for alternative materials.

一方、抵抗率がより高い透明導電膜は、電界を印加することでキャリアの制御が容易であることから、ＭＯＳトランジスタのチャンネル部に応用されている。このような透明導電膜の代表格としては非晶質半導体ＩｎＧａＺｎＯ4があり（例えば、非特許文献１参照）、その柔軟性を活かして、湾曲可能なディスプレイ用の薄膜トランジスタ（ＴＦＴ）や透明電極に適用されようとしているが、高抵抗率であることから透明電極には用いられていない。 On the other hand, a transparent conductive film having a higher resistivity is applied to a channel portion of a MOS transistor because carriers can be easily controlled by applying an electric field. A typical example of such a transparent conductive film is an amorphous semiconductor InGaZnO 4 (see, for example, Non-Patent Document 1). Taking advantage of its flexibility, it can be used as a thin film transistor (TFT) for display and a transparent electrode. Although it is about to be applied, it is not used for transparent electrodes because of its high resistivity.

K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, “Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors”, Nature, Vol.432, p.488-492, 2004年K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, “Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors”, Nature, Vol.432, p. .488-492, 2004

従来ではスパッタ法を用いて室温でＺｎＯ系透明導電膜を成膜していたが、従来技術のようにスパッタ法を用いて室温でＺｎＯ系透明導電膜を成膜した場合、部分的に結晶化が進行して、通常はｃ軸配向の結晶状態のＺｎＯ系透明導電膜が形成される。これはＣ面の表面エネルギーが低いこととも関係している。ここで、従来、ＺｎＯ系透明導電膜は結晶状態で形成されることから、機械的変形が与えられるフレキシブルデバイスへの利用には向かないとされてきた。しかし、ＺｎＯ系透明導電膜をフレキシブル基板の上に非晶質状態で形成できれば、フレキシブルデバイス用のＴＦＴや透明電極への利用が可能となる。   Conventionally, a ZnO-based transparent conductive film was formed at room temperature using a sputtering method. However, when a ZnO-based transparent conductive film was formed at room temperature using a sputtering method as in the prior art, it was partially crystallized. As a result, a ZnO-based transparent conductive film having a crystal state that is usually c-axis oriented is formed. This is also related to the low surface energy of the C plane. Here, conventionally, since the ZnO-based transparent conductive film is formed in a crystalline state, it has been considered unsuitable for use in a flexible device to which mechanical deformation is given. However, if the ZnO-based transparent conductive film can be formed on the flexible substrate in an amorphous state, it can be used for TFTs for transparent devices and transparent electrodes.

このような背景から、フレキシブルデバイス用のＴＦＴや透明電極として使用可能な非晶質状態のＺｎＯ系透明導電膜及びその形成方法の開発が課題であった。   From such a background, the development of an amorphous ZnO-based transparent conductive film that can be used as a TFT for a flexible device or a transparent electrode and a method for forming the same have been problems.

上記課題を解決するために、請求項１に記載の方法は、ＥｕドープＺｎＯ透明導電膜を作製する方法であって、スパッタ法により基板上にＺｎＯ膜中にＥｕがドープされたＥｕドープＺｎＯ透明導電膜を成膜するステップを含み、前記成膜するステップは、Ｈ 2 Ｏ蒸気ガスを導入しながら実行され、前記ＥｕドープＺｎＯ透明導電膜のＥｕドープ濃度は、１３ａｔ.％以上であることを特徴とする。 In order to solve the above-mentioned problem, the method according to claim 1 is a method for producing an Eu-doped ZnO transparent conductive film, and is a Eu-doped ZnO transparent in which Eu is doped in a ZnO film on a substrate by a sputtering method. it conductive film viewed including the steps of forming a step of the film formation is performed while introducing of H 2 O vapor gas, Eu doping concentration of the Eu-doped ZnO transparent conductive film is 13 atomic.% or more It is characterized by.

請求項２に記載の方法は、請求項１に記載の方法であって、当該成膜されたＥｕドープＺｎＯ透明導電膜を水素ガス雰囲気下、４００〜４５０℃の温度においてアニールするステップをさらに含むことを特徴とする。 The method according to claim 2 is the method according to claim 1, further comprising the step of annealing the formed Eu-doped ZnO transparent conductive film at a temperature of 400 to 450 ° C. in a hydrogen gas atmosphere. It is characterized by that.

本発明によると、薄膜トランジスタのゲート部、表示機器、太陽電池などに用いられるＺｎＯ系透明導電膜において、Ｅｕ3+という重い元素の３価イオンをドープすることで、ＺｎＯに導電性をもたらすとともに結晶性を低下させることができるため、非晶質状態の透明電極あるいはＴＦＴのゲート材料を得ることができる。また、水素ガス中でのポストアニールを併用することで、本発明に係る形成プロセスにおいて抵抗率が増大した場合であっても現実的に実用可能な抵抗値まで下げることが可能なため、湾曲可能かつ低抵抗なＴＦＴや透明電極としてフレキシブルデバイスへ適用する道を開くものである。 According to the present invention, ZnO-based transparent conductive film used for a gate portion of a thin film transistor, a display device, a solar cell, etc. is doped with a trivalent ion of a heavy element called Eu 3+ , thereby bringing conductivity into ZnO and crystal. Therefore, an amorphous transparent electrode or a TFT gate material can be obtained. In addition, by using post-annealing in hydrogen gas in combination, the resistance can be lowered to a practically practical resistance value even when the resistivity is increased in the formation process according to the present invention. And it opens the way to apply to flexible devices as low resistance TFTs and transparent electrodes.

酸素ガス導入なしで室温において成膜したＥｕドープＺｎＯ透明導電膜のキャリア密度、ホール移動度、抵抗率の膜厚依存性を例示する図である。It is a figure which illustrates the film thickness dependence of the carrier density of the Eu dope ZnO transparent conductive film formed into a film at room temperature without oxygen gas introduction | transduction, hole mobility, and a resistivity. 酸素ガス導入なしで２００℃において成膜したＥｕドープＺｎＯ透明導電膜のキャリア密度、ホール移動度、抵抗率の膜厚依存性を例示する図である。It is a figure which illustrates the film thickness dependence of the carrier density of the Eu dope ZnO transparent conductive film formed into a film at 200 degreeC without oxygen gas introduction | transduction, hole mobility, and a resistivity. 室温にてＥｕドープＺｎＯ透明導電膜を成膜する際にＯ2ガスあるいはＨ2Ｏガスを酸素源に用いた場合のＸ線回折パタンを示す図である。Is a diagram showing an X-ray diffraction pattern in the case of using the O 2 gas or the H 2 O gas in the oxygen source during the deposition of the Eu-doped ZnO transparent conductive film at room temperature. Ｈ2Ｏ蒸気ガスを用いて室温にて成膜した、各Ｅｕ濃度におけるＥｕドープＺｎＯ透明導電膜のＸ線回折パタンを例示する図である。It was deposited at room temperature using of H 2 O vapor gas is a diagram illustrating the X-ray diffraction pattern of the Eu-doped ZnO transparent conductive film in each Eu concentration. Ｏ2ガスを用いて室温にて成膜したＥｕドープＺｎＯ透明導電膜のシート抵抗と、当該ＥｕドープＺｎＯ透明導電膜をＨ2ガス中にてポストアニールした後のシート抵抗とのアニール温度依存性を例示する図である。Dependence of annealing temperature on sheet resistance of Eu-doped ZnO transparent conductive film formed at room temperature using O 2 gas and sheet resistance after post-annealing the Eu-doped ZnO transparent conductive film in H 2 gas FIG. Ｏ2ガスを用いて室温にて成膜したＥｕドープＺｎＯ透明導電膜のシート抵抗と、当該ＥｕドープＺｎＯ透明導電膜をＨ2ガス中にてポストアニールした後のシート抵抗とのアニール温度依存性を例示する図である。Dependence of annealing temperature on sheet resistance of Eu-doped ZnO transparent conductive film formed at room temperature using O 2 gas and sheet resistance after post-annealing the Eu-doped ZnO transparent conductive film in H 2 gas FIG. Ｈ2Ｏガスを用いて室温にて成膜したＥｕドープＺｎＯ透明導電膜のシート抵抗と、当該ＥｕドープＺｎＯ透明導電膜をＨ2ガス中にてポストアニールした後のシート抵抗とのアニール温度依存性を例示する図である。Dependence of annealing temperature on sheet resistance of Eu-doped ZnO transparent conductive film formed at room temperature using H 2 O gas and sheet resistance after post-annealing the Eu-doped ZnO transparent conductive film in H 2 gas It is a figure which illustrates sex. 本発明の実施例４に係るＥｕドープＺｎＯ透明導電膜形成方法を例示する図である。It is a figure which illustrates the Eu dope ZnO transparent conductive film formation method which concerns on Example 4 of this invention.

上記課題を解決するために、本発明においては、希土類元素であるＥｕをＺｎＯ系透明導電膜へのドーパントとして用いる。Ｅｕ3+イオンがＺｎ2+サイトに置換することでＥｕ3+イオンがドナーとして働くことが期待されるが、ドナー準位はＧａ3+やＡｌ3+に比べてバンドギャップの深い位置にあると予想される。そのため、Ｅｕ3+イオンがＺｎＯ中で本当にドナーとして働くかどうかは自明ではなかった。しかし、本発明によりドナーとして機能することが実証された。 In order to solve the above problems, in the present invention, Eu, which is a rare earth element, is used as a dopant for the ZnO-based transparent conductive film. While Eu 3+ ion is Eu 3+ ions by substituting Zn 2+ site is expected to serve as a donor, the donor level is in a deep position in the band gap as compared to Ga 3+ and Al 3+ It is expected to be. Therefore, it was not obvious whether Eu 3+ ions really act as donors in ZnO. However, it has been demonstrated by the present invention to function as a donor.

一方で、Ｅｕ3+のイオン半径はＺｎ2+のイオン半径よりもかなり大きいため、サイト置換したＥｕ3+イオンはＺｎＯ結晶格子に歪みを及ぼす。その影響は、イオン半径が比較的小さなＧａ3+イオンやＡｌ3+イオンをドープした場合に比べて甚大である。結果として、ＧａドープＺｎＯやＡｌドープＺｎＯに比べてＥｕドープＺｎＯの結晶性は悪くなる。さらに、Ｅｕ3+の価数がＺｎ2+の価数と異なることも影響して、少量だけがＺｎ2+サイトに置換することができ、ＺｎＯ結晶子内に収容しきれなかったＥｕ3+イオンは結晶子の外へ放出されることになる。粒界にＥｕ2Ｏ3が析出されると、ＺｎＯの結晶子サイズは必然的に小さくなる。これらの効果が相まって、Ｅｕ濃度がおよそ１０ａｔ.％を超えると、ＺｎＯ結晶は非晶質状態になる。 On the other hand, since the ionic radius of Eu 3+ is considerably larger than that of Zn 2+ , site-substituted Eu 3+ ions distort the ZnO crystal lattice. The influence is enormous compared with the case where Ga 3+ ions or Al 3+ ions having a relatively small ion radius are doped. As a result, the crystallinity of Eu-doped ZnO is worse than Ga-doped ZnO or Al-doped ZnO. Furthermore, due to the fact that the valence of Eu 3+ is different from the valence of Zn 2+ , only a small amount can be substituted for the Zn 2+ site, and Eu 3+ that could not be accommodated in the ZnO crystallites. The ions will be released out of the crystallite. When Eu 2 O 3 is precipitated at the grain boundary, the crystallite size of ZnO is inevitably reduced. When these effects are combined and the Eu concentration exceeds approximately 10 at.%, The ZnO crystal becomes amorphous.

また、ＺｎＯの結晶性は、成膜時の雰囲気にも影響される。従来のスパッタ法による成膜においては、真空中の還元雰囲気下でＺｎＯ膜を形成するため、ｃ軸配向の結晶性の良いＺｎＯ膜が得られる。一方、酸素源となるガスを導入してＺｎＯ膜を形成すると、ＺｎＯ膜がランダム配向になりやすく、非晶質状態にしやすい。特に、Ｈ2Ｏガスを用いることで、ＺｎＯの結晶性を効率的に低下させることができ、非晶質状態のＺｎＯ系透明導電膜を形成しやすくなる。 The crystallinity of ZnO is also affected by the atmosphere during film formation. In the film formation by the conventional sputtering method, a ZnO film is formed in a reducing atmosphere in a vacuum, so that a ZnO film having good c-axis orientation crystallinity can be obtained. On the other hand, when a gas serving as an oxygen source is introduced to form a ZnO film, the ZnO film tends to be in a random orientation and easily in an amorphous state. In particular, by using H 2 O gas, the crystallinity of ZnO can be efficiently reduced, and an amorphous ZnO-based transparent conductive film can be easily formed.

しかし、以上のような方法によってＺｎＯ膜の結晶性を低下させた場合、電子の移動度が低下する。また、Ｈ2Ｏ蒸気などのガスによりＺｎＯ膜を過剰酸化することで、キャリア密度も低下する。その結果、ＺｎＯ膜の電気伝導性が悪くなり、透明導電膜としては使えない場合があるという課題に直面する。そこで、水素中にて４００〜４５０℃でポストアニールすることで、ＺｎＯ膜を部分的に還元し、Ｅｕ3+イオンのドナーとしての働きを回復させることができる。 However, when the crystallinity of the ZnO film is lowered by the method as described above, the electron mobility is lowered. Further, the carrier density is also lowered by excessively oxidizing the ZnO film with a gas such as H 2 O vapor. As a result, the electrical conductivity of the ZnO film is deteriorated, and the problem that it may not be used as a transparent conductive film is encountered. Therefore, by performing post-annealing in hydrogen at 400 to 450 ° C., the ZnO film can be partially reduced and the function as a donor of Eu 3+ ions can be recovered.

以下、本発明の有効性を示すために、本発明に係るＥｕドープＺｎＯ透明導電膜について、ＥｕドープＺｎＯ透明導電膜の形成とその電気伝導性の評価を行った。電気的特性は、下記実施例１乃至３に係る方法で作製された低抵抗試料についてはホール効果測定により評価し、下記実施例４に係る方法で作製された高抵抗試料については四端子法によってシート抵抗を測定した。   Hereinafter, in order to show the effectiveness of the present invention, formation of an Eu-doped ZnO transparent conductive film and evaluation of its electrical conductivity were performed on the Eu-doped ZnO transparent conductive film according to the present invention. The electrical characteristics were evaluated by Hall effect measurement for the low resistance samples prepared by the methods according to Examples 1 to 3 below, and the four resistance method for the high resistance samples prepared by the method according to Example 4 below. Sheet resistance was measured.

以下の実施例では、濃度１ａｔ.％のＥｕを含有するＺｎＯターゲットとＥｕ2Ｏ3ターゲットからの共スパッタにより高抵抗基板上へ成膜することにより、各実施例に係るＥｕドープＺｎＯ透明導電膜を作製した。Ｅｕ2Ｏ3ターゲットヘのスパッタパワーを増やすことでＺｎＯ膜中のＥｕ濃度を増やすことが可能である。基板の抵抗は十分に大きいため、電気伝導性はＺｎＯ膜から生じている。 In the following examples, the Eu-doped ZnO transparent conductive film according to each example is formed by forming a film on a high-resistance substrate by co-sputtering from a ZnO target containing Eu at a concentration of 1 at.% And an Eu 2 O 3 target. Was made. It is possible to increase the Eu concentration in the ZnO film by increasing the sputtering power to the Eu 2 O 3 target. Since the resistance of the substrate is sufficiently large, the electrical conductivity comes from the ZnO film.

（実施例１）
図１及び図２を用いて、本発明の実施例１に係るＥｕドープＺｎＯ透明導電膜について説明する。本発明の実施例１に係るＥｕドープＺｎＯ透明導電膜は、スパッタ法を用いて基板上に形成される。図１は、酸素ガス導入なしの条件で、高抵抗Ｓｉ（１００）基板上に室温において成膜したＥｕ濃度０．９ａｔ.％のＥｕドープＺｎＯ透明導電膜のキャリア密度ｎ、ホール移動度μ及び抵抗率ρの膜厚依存性を示す。図１には、膜厚の増加に伴ってキャリア密度ｎ及びホール移動度μは増大し、抵抗率ρは減少するという透明導電膜の一般的な特徴が表れている。図１に示されるように、膜厚１００ｎｍにおいて２ｍΩ・ｃｍの抵抗率ρが得られている。 Example 1
The Eu-doped ZnO transparent conductive film according to Example 1 of the present invention will be described with reference to FIGS. 1 and 2. The Eu-doped ZnO transparent conductive film according to Example 1 of the present invention is formed on a substrate using a sputtering method. FIG. 1 shows a carrier density n, a hole mobility μ and an Eu-doped ZnO transparent conductive film with an Eu concentration of 0.9 at.% Formed on a high-resistance Si (100) substrate at room temperature without introducing oxygen gas. The film thickness dependence of resistivity ρ is shown. FIG. 1 shows a general characteristic of the transparent conductive film that the carrier density n and the hole mobility μ increase and the resistivity ρ decreases as the film thickness increases. As shown in FIG. 1, a resistivity ρ of 2 mΩ · cm is obtained at a film thickness of 100 nm.

ここで、同じ成膜装置を用いて同じ成膜条件で得られた膜厚１００ｎｍのアンドープＺｎＯ膜の抵抗率は４．５ｍΩ・ｃｍであったため、Ｅｕ3+はドナーとして働いていることが分かる。 Here, since the resistivity of the 100 nm-thick undoped ZnO film obtained under the same film formation conditions using the same film formation apparatus was 4.5 mΩ · cm, it can be seen that Eu 3+ works as a donor. .

Ｅｕ3+がＥｕドープＺｎＯ中でドナーとして働いていることをさらに示すために、図１で用いた条件に対して成膜温度を変更した場合の結果を図２を用いて示す。図２は、酸素ガス導入なしの条件で、高抵抗Ｓｉ（１００）基板上に２００℃において成膜したＥｕ濃度０．９ａｔ.％のＥｕドープＺｎＯ透明導電膜のキャリア密度ｎ、ホール移動度μ及び抵抗率ρの膜厚依存性を示す。図２に示す結果では、図１に示す結果と類似した傾向の特性が得られているが、膜厚１００ｎｍにおける抵抗率ρは６ｍΩ・ｃｍと高くなっている。しかし、アンドープＺｎＯ膜の場合（図２では不図示）、２００℃で成膜すると抵抗率ρは０．４Ω・ｃｍと、図２において２００℃で成膜されたＥｕドープＺｎＯ透明導電膜の抵抗率ρよりはるかに高い値を取る。 In order to further show that Eu 3+ works as a donor in Eu-doped ZnO, the results when the film formation temperature is changed with respect to the conditions used in FIG. 1 are shown in FIG. FIG. 2 shows the carrier density n and hole mobility μ of an Eu-doped ZnO transparent conductive film with an Eu concentration of 0.9 at.% Formed on a high resistance Si (100) substrate at 200 ° C. without introducing oxygen gas. And the film thickness dependence of resistivity ρ. In the result shown in FIG. 2, characteristics having a tendency similar to the result shown in FIG. 1 are obtained, but the resistivity ρ at a film thickness of 100 nm is as high as 6 mΩ · cm. However, in the case of an undoped ZnO film (not shown in FIG. 2), the resistivity ρ is 0.4 Ω · cm when formed at 200 ° C., and the resistance of the Eu-doped ZnO transparent conductive film formed at 200 ° C. in FIG. Takes a value much higher than the rate ρ.

ここで、アンドープＺｎＯ膜においては、酸素空孔や格子間亜鉛などの内因性ドナーによって伝導性が発現している。アニールによって格子間に存在する酸素原子が熱拡散して酸素空孔と再結合して格子の組み換えが起きると、ドナー源である欠陥が消滅する。一方、外因性ドナーであるＥｕ3+により伝導性がもたらされているＥｕドープＺｎＯ透明導電膜に関しては、酸化度がＥｕ3+の活性化に一定の影響を与えているものの、アンドープＺｎＯ膜における酸素空孔の消滅ほど直接的な影響がない。そのため、成膜温度の上昇による抵抗率ρの増大も、室温で成膜した場合の２ｍΩ・ｃｍから２００℃で成膜した場合の６ｍΩ・ｃｍと、微幅に留まっているものと解釈することができる。このように、成膜温度の影響が少ないことも、Ｅｕ3+がＥｕドープＺｎＯ中でドナーとして働いていることを証明している。 Here, in the undoped ZnO film, conductivity is expressed by intrinsic donors such as oxygen vacancies and interstitial zinc. When oxygen atoms existing between lattices are thermally diffused by annealing and recombined with oxygen vacancies to cause recombination of lattices, defects that are donor sources disappear. On the other hand, regarding the Eu-doped ZnO transparent conductive film in which conductivity is provided by Eu 3+ which is an exogenous donor, although the degree of oxidation has a certain influence on the activation of Eu 3+ , the undoped ZnO film Is not as direct as the disappearance of oxygen vacancies. Therefore, the increase in resistivity ρ due to an increase in film formation temperature should be interpreted as being only a small range from 2 mΩ · cm when formed at room temperature to 6 mΩ · cm when formed at 200 ° C. Can do. Thus, the small influence of the film formation temperature also proves that Eu 3+ works as a donor in Eu-doped ZnO.

（実施例２）
図３を用いて、本発明の実施例２に係るＥｕドープＺｎＯ透明導電膜について説明する。実施例２に係るＥｕドープＺｎＯ透明導電膜は、酸素源としてガスを導入しながら基板上に成膜される。それにより、上述のようにＺｎＯ膜がランダム配向になりやすく、ＺｎＯ膜を非晶質状態にしやすくなる。 (Example 2)
An Eu-doped ZnO transparent conductive film according to Example 2 of the present invention will be described with reference to FIG. The Eu-doped ZnO transparent conductive film according to Example 2 is formed on the substrate while introducing a gas as an oxygen source. As a result, the ZnO film is likely to be randomly oriented as described above, and the ZnO film is likely to be in an amorphous state.

図３は、サファイアＣ面基板上に室温にてＥｕ濃度２ａｔ.％のＥｕドープＺｎＯ透明導電膜を成膜する際に、酸素ガス又はＨ2Ｏ蒸気ガスを酸素源に用いた場合のＥｕドープＺｎＯ透明導電膜のＸ線回折パタンを例示する。図３に示されるように、実施例２に係るＥｕドープＺｎＯ透明導電膜では、ＺｎＯ（００２）ピークの強度は、Ｈ2Ｏガスで成膜した場合には、酸素ガスで成膜した場合に比べて２桁以上小さくなっている。ここで、ガスを導入しないでＥｕドープＺｎＯ透明導電膜を成膜した場合は酸素ガスで成膜した場合と同程度の結果が得られることが知られている。よって、有利にはＨ2Ｏガスを用いることで、ＺｎＯの結晶性を効率的に低下させることができ、ＺｎＯ膜の非晶質化がより促進されることが分かる。 FIG. 3 shows Eu doping when oxygen gas or H 2 O vapor gas is used as an oxygen source when forming an Eu-doped ZnO transparent conductive film having a Eu concentration of 2 at. The X-ray diffraction pattern of a ZnO transparent conductive film is illustrated. As shown in FIG. 3, in the Eu-doped ZnO transparent conductive film according to Example 2, the intensity of the ZnO (002) peak is as follows when the film is formed with H 2 O gas and when the film is formed with oxygen gas. Compared to two orders of magnitude smaller. Here, it is known that when an Eu-doped ZnO transparent conductive film is formed without introducing a gas, results similar to those obtained when an oxygen gas film is formed are obtained. Therefore, it can be seen that the use of H 2 O gas advantageously makes it possible to efficiently reduce the crystallinity of ZnO and promote the amorphization of the ZnO film.

（実施例３）
図４を用いて、本発明の実施例３に係るＥｕドープＺｎＯ透明導電膜について説明する。実施例３に係るＥｕドープＺｎＯ透明導電膜は、Ｅｕを高濃度ドープすることによって成膜される。それにより、ＺｎＯ膜の非晶質化をより促進することができる。 (Example 3)
The Eu-doped ZnO transparent conductive film according to Example 3 of the present invention will be described with reference to FIG. The Eu-doped ZnO transparent conductive film according to Example 3 is formed by highly doping Eu. Thereby, the amorphization of the ZnO film can be further promoted.

図４は、Ｈ2Ｏ蒸気ガスを用いて高抵抗Ｓｉ（１００）基板上に室温にて成膜したＥｕドープＺｎＯ透明導電膜中のＥｕ濃度を４．３ａｔ.％、７．８ａｔ.％、１３ａｔ.％と増大させたときのＸ線回折パタンを例示する。図４に示されるように、Ｈ2Ｏ蒸気ガスを使用しているため既にＺｎＯ（００２）ピーク強度は比較的小さいが、１３ａｔ.％とＥｕを高濃度ドープすると、ＺｎＯ（００２）回折ピークは完全に消滅し、非晶質状態になっていることが分かる。このように、Ｅｕを高濃度ドープすることによってＺｎＯ膜の非晶質化をより促進することができる。ここで、Ｅｕ濃度がおよそ１０ａｔ.％を超えるとＺｎＯ結晶は非晶質状態になるため、Ｅｕ濃度は１０ａｔ.％以上が好ましく、完全に非晶質状態になるためには１３ａｔ.％以上であることがより好ましい。 FIG. 4 shows that the Eu concentration in the Eu-doped ZnO transparent conductive film formed at room temperature on a high resistance Si (100) substrate using H 2 O vapor gas is 4.3 at.%, 7.8 at.%, The X-ray diffraction pattern when increased to 13 at. As shown in FIG. 4, since the H 2 O vapor gas is used, the ZnO (002) peak intensity is already relatively small, but when doping at a high concentration of 13 at.% And Eu, the ZnO (002) diffraction peak is It can be seen that it has completely disappeared and is in an amorphous state. As described above, the amorphous doping of the ZnO film can be further promoted by highly doping Eu. Here, since the ZnO crystal becomes amorphous when the Eu concentration exceeds approximately 10 at.%, The Eu concentration is preferably 10 at.% Or more, and in order to be completely amorphous, it is 13 at.% Or more. More preferably.

（実施例４）
図５乃至図８を用いて、本発明の実施例４に係るＥｕドープＺｎＯ透明導電膜について説明する。上述のように、実施例２又は３の方法によりＺｎＯ膜の結晶性を低下させた場合、ＺｎＯ膜の電気伝導性が悪くなり、透明導電膜としては使えない場合がある。 Example 4
An Eu-doped ZnO transparent conductive film according to Example 4 of the present invention will be described with reference to FIGS. As described above, when the crystallinity of the ZnO film is lowered by the method of Example 2 or 3, the electrical conductivity of the ZnO film is deteriorated and may not be used as a transparent conductive film.

図８は、本発明の実施例４に係るＥｕドープＺｎＯ透明導電膜形成方法を示す。図８に示されるように、本発明の実施例４に係るＥｕドープＺｎＯ透明導電膜は、ステップ８０１で、酸素源となるガスを導入しつつスパッタ法を用いて成膜されたＥｕドープＺｎＯ透明導電膜を形成する。次に、ステップ８０２で、ステップ８０１で作製したＥｕドープＺｎＯ透明導電膜を、水素ガス雰囲気下、４００〜４５０℃の温度においてポストアニールする。それにより、実施例４に係るＥｕドープＺｎＯ透明導電膜においては、実施例２又は３の方法によって電気伝導性が悪くなったＥｕドープＺｎＯ透明導電膜を部分的に還元し、Ｅｕ3+イオンのドナーとしての働きを回復させることができる。 FIG. 8 shows a method for forming an Eu-doped ZnO transparent conductive film according to Example 4 of the present invention. As shown in FIG. 8, the Eu-doped ZnO transparent conductive film according to Example 4 of the present invention is a Eu-doped ZnO transparent film formed by sputtering in step 801 while introducing a gas serving as an oxygen source. A conductive film is formed. Next, in Step 802, the Eu-doped ZnO transparent conductive film produced in Step 801 is post-annealed at a temperature of 400 to 450 ° C. in a hydrogen gas atmosphere. Thereby, in the Eu-doped ZnO transparent conductive film according to Example 4, the Eu-doped ZnO transparent conductive film whose electrical conductivity was deteriorated by the method of Example 2 or 3 was partially reduced, and Eu 3+ ion The work as a donor can be restored.

図５は、酸素ガスを用いて高抵抗Ｓｉ（１００）基板上に室温にて成膜したＥｕ濃度５ａｔ.％のＥｕドープＺｎＯ透明導電膜のシート抵抗と、当該ＥｕドープＺｎＯ透明導電膜を水素ガス中にて１時間ポストアニールした後のシート抵抗とのアニール温度依存性を示す。図５では、酸素ガスを用いて室温にて成膜したＥｕ濃度５ａｔ.％のＥｕドープＺｎＯ透明導電膜のシート抵抗のアニール温度依存性を特性５０１として示し、当該ＥｕドープＺｎＯ透明導電膜を水素ガス中にて１時間ポストアニールした後の実施例４に係るＥｕドープＺｎＯ透明導電膜のシート抵抗のアニール温度依存性を特性５０２として示す。   FIG. 5 shows a sheet resistance of an Eu-doped ZnO transparent conductive film having an Eu concentration of 5 at.% Formed on a high-resistance Si (100) substrate using oxygen gas at room temperature, and the Eu-doped ZnO transparent conductive film is hydrogenated. The annealing temperature dependence with the sheet resistance after 1 hour post-annealing in gas is shown. In FIG. 5, the annealing temperature dependence of the sheet resistance of an Eu-doped ZnO transparent conductive film having an Eu concentration of 5 at.% Deposited at room temperature using oxygen gas is shown as a characteristic 501, and the Eu-doped ZnO transparent conductive film is represented by hydrogen. The annealing temperature dependence of the sheet resistance of the Eu-doped ZnO transparent conductive film according to Example 4 after post-annealing in gas for 1 hour is shown as a characteristic 502.

図５の特性５０２に示されるように、アニール温度３００℃まではアニールの効果はないが、３５０℃、４００℃、４５０℃において、シート抵抗が著しく減少している。特に、４００℃及び４５０℃のアニール後には、３００〜４００Ω/□といった透明導電膜として十分実用になるレベルの低い抵抗値が得られている。このように、温度が４００℃〜４５０℃の範囲のアニーリングにおいて、解離した水素原子が余分な酸素を除き、Ｅｕ3+がドナーとして活性化したものと考えられる。そのため、本実施例に係るＥｕドープＺｎＯ透明導電膜によると、実施例２又は３の方法で非晶質化されたＥｕドープＺｎＯ透明導電膜の抵抗値を十分実用になるレベルの低い抵抗値に低減することができる。 As shown by the characteristic 502 in FIG. 5, there is no annealing effect up to the annealing temperature of 300 ° C., but the sheet resistance is remarkably reduced at 350 ° C., 400 ° C., and 450 ° C. In particular, after annealing at 400 ° C. and 450 ° C., a low resistance value of 300 to 400 Ω / □, which is a sufficiently practical level as a transparent conductive film, is obtained. As described above, it is considered that Eu 3+ is activated as a donor by removing the excess oxygen from the dissociated hydrogen atoms in the annealing in the temperature range of 400 ° C. to 450 ° C. Therefore, according to the Eu-doped ZnO transparent conductive film according to this example, the resistance value of the Eu-doped ZnO transparent conductive film amorphized by the method of Example 2 or 3 is set to a low resistance value that is sufficiently practical. Can be reduced.

図６を用いて、本発明の実施例４の他の例に係るＥｕドープＺｎＯ透明導電膜について説明する。本発明の実施例４の他の例に係るＥｕドープＺｎＯ透明導電膜は、酸素ガスを導入しつつスパッタ法を用いて高抵抗Ｓｉ（１００）基板上に成膜されたＥｕ濃度１４ａｔ.％のＥｕドープＺｎＯ透明導電膜を、水素ガス雰囲気下、４００〜４５０℃の温度においてポストアニールすることにより作製される。図６は、酸素ガスを用いて室温にて成膜したＥｕ濃度１４ａｔ.％のＥｕドープＺｎＯ透明導電膜のシート抵抗と、当該ＥｕドープＺｎＯ透明導電膜を水素ガス中にて１時間ポストアニールした後のシート抵抗とのアニール温度依存性を例示する。図６では、酸素ガスを用いて室温にて成膜したＥｕ濃度１４ａｔ.％のシート抵抗のアニール温度依存性を特性６０１として示し、当該ＥｕドープＺｎＯ透明導電膜を水素ガス中にて１時間ポストアニールした後のＥｕドープＺｎＯ透明導電膜のシート抵抗のアニール温度依存性を特性６０２として示す。また、図６では、Ｅｕ濃度が１４ａｔ.％と高濃度にドープしたＥｕドープＺｎＯ透明導電膜を用いており、このＥｕドープＺｎＯ透明導電膜は非晶質状態である。   An Eu-doped ZnO transparent conductive film according to another example of Example 4 of the present invention will be described with reference to FIG. An Eu-doped ZnO transparent conductive film according to another example of Example 4 of the present invention has an Eu concentration of 14 at.% Formed on a high resistance Si (100) substrate by sputtering while introducing oxygen gas. The Eu-doped ZnO transparent conductive film is produced by post-annealing at a temperature of 400 to 450 ° C. in a hydrogen gas atmosphere. FIG. 6 shows a sheet resistance of an Eu-doped ZnO transparent conductive film with an Eu concentration of 14 at.% Formed at room temperature using oxygen gas, and the Eu-doped ZnO transparent conductive film was post-annealed in hydrogen gas for 1 hour. The annealing temperature dependence with subsequent sheet resistance is illustrated. In FIG. 6, the annealing temperature dependence of the sheet resistance with an Eu concentration of 14 at.% Deposited at room temperature using oxygen gas is shown as a characteristic 601, and the Eu-doped ZnO transparent conductive film is post-treated in hydrogen gas for 1 hour The annealing temperature dependence of the sheet resistance of the Eu-doped ZnO transparent conductive film after annealing is shown as a characteristic 602. In FIG. 6, an Eu-doped ZnO transparent conductive film doped with a high Eu concentration of 14 at.% Is used, and this Eu-doped ZnO transparent conductive film is in an amorphous state.

図６の特性６０２に示されるように、４００〜４５０℃のアニールの後に３００〜５００Ω/□までシート抵抗が減少しており、透明導電膜として十分実用になるレベルの低い抵抗値が得られている。このように、水素中でアニールすることで、シート抵抗が減少することは明らかである。   As shown by the characteristic 602 in FIG. 6, the sheet resistance decreases to 300 to 500 Ω / □ after annealing at 400 to 450 ° C., and a low resistance value that is sufficiently practical for a transparent conductive film is obtained. Yes. Thus, it is clear that the sheet resistance decreases by annealing in hydrogen.

一方で、アニールを真空中で行うと抵抗の減少はほとんど見られず、あるいは酸素ガス中でアニールした場合には、むしろ高抵抗化した（図６では不図示）。則ち、抵抗を減らすためには、水素中でのアニールが本質的である。   On the other hand, when the annealing is performed in a vacuum, the resistance is hardly decreased, or when the annealing is performed in oxygen gas, the resistance is rather increased (not shown in FIG. 6). In other words, annealing in hydrogen is essential to reduce resistance.

図７を用いて、本発明の実施例４のさらに他の例に係るＥｕドープＺｎＯ透明導電膜について説明する。本発明の実施例４のさらに他の例に係るＥｕドープＺｎＯ透明導電膜は、実施例２のＨ2Ｏ蒸気ガスを導入しつつスパッタ法を用いて高抵抗Ｓｉ（１００）基板上に成膜されたＥｕ濃度５ａｔ.％のＥｕドープＺｎＯ透明導電膜を、水素ガス雰囲気下、４００〜４５０℃の温度においてポストアニールすることにより作製される。図７はＨ2Ｏ蒸気ガスを用いて室温にて成膜したＥｕ濃度５ａｔ.％のＥｕドープＺｎＯ透明導電膜のシート抵抗と、当該ＥｕドープＺｎＯ透明導電膜を水素ガス中にて１時間ポストアニールした後のシート抵抗とのアニール温度依存性を例示する。図７では、Ｈ2Ｏ蒸気ガスを用いて室温にて成膜したＥｕ濃度５ａｔ.％のＥｕドープＺｎＯ透明導電膜のシート抵抗のアニール温度依存性を特性７０１として示し、当該ＥｕドープＺｎＯ透明導電膜を水素ガス中にて１時間ポストアニールした後のＥｕドープＺｎＯ透明導電膜のシート抵抗のアニール温度依存性を特性７０２として示す。 An Eu-doped ZnO transparent conductive film according to still another example of Example 4 of the present invention will be described with reference to FIG. An Eu-doped ZnO transparent conductive film according to still another example of Example 4 of the present invention is formed on a high-resistance Si (100) substrate by sputtering while introducing the H 2 O vapor gas of Example 2. The Eu-doped ZnO transparent conductive film having an Eu concentration of 5 at.% Is produced by post-annealing at a temperature of 400 to 450 ° C. in a hydrogen gas atmosphere. FIG. 7 shows the sheet resistance of an Eu-doped ZnO transparent conductive film with an Eu concentration of 5 at.% Formed at room temperature using H 2 O vapor gas, and the Eu-doped ZnO transparent conductive film is post-posted in hydrogen gas for 1 hour. The annealing temperature dependence with the sheet resistance after annealing is illustrated. In FIG. 7, the annealing temperature dependence of the sheet resistance of the Eu-doped ZnO transparent conductive film with an Eu concentration of 5 at.% Formed at room temperature using H 2 O vapor gas is shown as a characteristic 701. The annealing temperature dependence of the sheet resistance of the Eu-doped ZnO transparent conductive film after post-annealing the film in hydrogen gas for 1 hour is shown as a characteristic 702.

図７の特性７０２に示されるように、やはり３５０〜４５０℃の範囲において、シート抵抗の低下が観測されており、この場合、最終的な値は１ｋΩ/□程度に留まっている。このように、本発明に係るポストアニールの温度は、３５０〜４５０℃の範囲が好適である。   As shown by the characteristic 702 in FIG. 7, a decrease in sheet resistance is also observed in the range of 350 to 450 ° C. In this case, the final value remains at about 1 kΩ / □. Thus, the post-annealing temperature according to the present invention is preferably in the range of 350 to 450 ° C.

Claims (2)

ＥｕドープＺｎＯ透明導電膜を作製する方法であって、
スパッタ法により基板上にＺｎＯ膜中にＥｕがドープされたＥｕドープＺｎＯ透明導電膜を成膜するステップを含み、
前記成膜するステップは、Ｈ 2 Ｏ蒸気ガスを導入しながら実行され、
前記ＥｕドープＺｎＯ透明導電膜のＥｕドープ濃度は、１３ａｔ.％以上であることを特徴とする方法。 A method for producing a Eu-doped ZnO transparent conductive film,
Look including the step of Eu in the ZnO film on a substrate forming a Eu-doped ZnO transparent conductive film doped by sputtering,
The film forming step is performed while introducing H 2 O vapor gas,
The Eu doping concentration of the Eu-doped ZnO transparent conductive film is 13 at.% Or more . 当該成膜されたＥｕドープＺｎＯ透明導電膜を水素ガス雰囲気下、４００〜４５０℃の温度においてアニールするステップをさらに含むことを特徴とする請求項１に記載の方法。 The method of claim 1, further comprising annealing the deposited Eu-doped ZnO transparent conductive film in a hydrogen gas atmosphere at a temperature of 400 to 450 ° C.
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