KR102196736B1 - Reflective anode for organic el display - Google Patents

Abstract

[Problem] A novel Al alloy reflective film capable of securing low contact resistance and high reflectivity while reducing the electrical resistivity of the Al alloy reflective film itself even if the Al alloy reflective film is directly in contact with an oxide conductive film such as ITO or IZO. A reflective anode electrode for an organic EL display is provided.
[Solution] An organic EL display comprising a lamination structure including an Al-Ge alloy film and an oxide conductive film in contact with the Al-Ge alloy film, and interposing a layer containing aluminum oxide as a main component at the contact interface thereof The Al-Ge-based alloy film contains 0.1 to 2.5 atomic% Ge, and a Ge enriched layer and a Ge-containing precipitate are formed at the contact interface between the Al-Ge-based alloy film and the oxide conductive film. , The average Ge concentration within 50 nm from the surface of the oxide conductive film side in the Al-Ge-based alloy film is at least twice the average Ge concentration in the Al-Ge-based alloy film, and the average diameter of the Ge-containing precipitate is It is 0.1㎛ or more.

Description

Reflective anode for organic EL display {REFLECTIVE ANODE FOR ORGANIC EL DISPLAY}

The present invention relates to a reflective anode electrode, a thin film transistor substrate, an organic EL display, and a sputtering target used in an organic EL display (especially a top emission type).

An organic EL (Organic Electro-Luminescence) display, one of the self-luminous flat panel displays, is an all-solid flat panel formed by arranging organic EL elements in a matrix on a substrate such as a glass plate. It is a display. In an organic EL display, an anode (anode) and a cathode (cathode) are formed in a stripe shape, and a portion where they intersect corresponds to a pixel (organic EL element). By applying a voltage of several V from the outside to this organic EL device to make a current flow, the organic molecules are pushed up to an excited state, and their excess energy is emitted as light when it returns to its original ground state (stable state). . This luminous color is unique to organic materials.

The organic EL element is a self-luminous type and a current-driven element, but there are a passive type and an active type as a driving method thereof. The passive type has a simple structure, but it is difficult to achieve full color. On the other hand, the active type can be enlarged and is suitable for full color, but the active type requires a thin film transistor (TFT) substrate. In addition, TFTs such as low-temperature polycrystalline Si (p-Si) or amorphous Si (a-Si) are used for this TFT substrate.

In the case of this active type organic EL display, a plurality of TFTs and wirings are obstructed, and the area usable for the organic EL pixel becomes small. When the driving circuit becomes complicated and the number of TFTs increases, the influence becomes even greater. In recent years, attention has been paid to a method of improving the aperture ratio by not taking out light from a glass substrate but taking out light from the top surface side (top emission).

In the top emission, ITO (Indium Tin Oxide) excellent in hole injection is used for the anode (anode) on the lower surface. Further, although it is necessary to use a transparent conductive film for the cathode (cathode) on the upper surface, ITO has a large work function and is not suitable for electron injection. Further, since ITO is formed by a sputtering method or an ion beam evaporation method, there is a concern that plasma ions and electron secondary electrons during film formation may damage the electron transport layer (an organic material constituting an organic EL element). Therefore, by forming a thin Mg layer or a copper phthalocyanine layer on the electron transport layer, damage is avoided and electron injection is improved.

The anode electrode used in such an active matrix type top emission organic EL display serves the purpose of reflecting the light emitted from the organic EL element, and is a transparent oxide conductive represented by ITO and IZO (Indium Zinc Oxide). It has a laminated structure of a film and a reflective film (reflective anode electrode). The reflective film used in this reflective anode electrode is often a reflective metal film such as molybdenum (Mo), chromium (Cr), aluminum (Al) or silver (Ag). For example, a laminated structure of ITO and Ag alloy films is adopted as a reflective anode electrode in a top emission type organic EL display that has already been mass-produced.

Considering the reflectance, Ag or an Ag-based alloy containing Ag as a main substance is useful because its reflectance is high. Further, the Ag-based alloy has a unique problem in that the corrosion resistance is inferior, but the aforementioned problem can be solved by covering the Ag-based alloy film with an ITO film laminated thereon. However, since Ag has a high material cost and it is difficult to increase the size of the sputtering target required for film formation, it is difficult to apply an Ag-based alloy film to an active matrix type top emission organic EL display reflective film for a large TV. .

On the other hand, considering only the reflectance, Al is also good as a reflective film. For example, Patent Document 1 discloses an Al film or an Al-Nd film as a reflective film, and describes that the Al-Nd film has excellent reflectance and is preferable.

However, when the Al reflective film is in direct contact with an oxide conductive film such as ITO or IZO, the contact resistance (contact resistance) is high, and sufficient current cannot be supplied for hole injection into the organic EL element. In order to avoid this, if a high melting point metal such as Mo or Cr other than Al is used for the reflective film, or a high melting point metal such as Mo or Cr is provided as a barrier metal between the Al reflective film and the oxide conductive film, the reflectance is significantly deteriorated. It causes a decrease in the luminance of light emission, which is a display characteristic.

Therefore, in Patent Document 2, an Al-Ni alloy film containing 0.1 to 2 atomic% of Ni is proposed as a reflective electrode (reflective film) from which a barrier metal can be omitted. According to this, it has a high reflectivity as high as pure Al, and a low contact resistance can be achieved even when the Al reflective film is directly contacted with an oxide conductive film such as ITO or IZO.

In addition, as in Patent Document 2, as a reflective electrode (reflective film) capable of omitting a barrier metal, in Patent Document 3, an Al-Ag alloy film containing 0.1 to 6 atomic% of Ag is proposed. Alternatively, in Patent Document 4, an Al-Ge-(Gd, La) alloy film containing 0.05 to 0.5 atomic% of Ge and 0.05 to 0.45 atomic% of Gd and/or La in total is proposed.

Japanese Patent Publication No. 2005-259695 Japanese Patent Publication No. 2008-122941 Japanese Patent Publication No. 2011-108459 Japanese Patent Publication No. 2008-160058

By the way, in the top emission type organic EL display, when an Al alloy is used as the anode electrode, an insulating oxide film (a layer mainly composed of aluminum oxide), which is inevitably formed on the surface of the Al alloy in the presence of oxygen, is the cause. There is a problem that it becomes difficult to flow. In this case, if a current equal to or greater than a predetermined value is to be passed, the voltage value required to pass the current increases, and thus there is a problem that power consumption increases when the same light emission intensity is maintained.

Further, as a characteristic required for the anode electrode, it is mentioned that the electrical resistivity of the Al alloy reflective film itself constituting the anode electrode is low.

The present invention has been made in view of the above circumstances, and its object is to reduce the electrical resistivity of the Al alloy reflective film itself, even when the Al alloy reflective film is directly contacted with an oxide conductive film such as ITO or IZO, while maintaining low contact resistance and high It is to provide a reflective anode electrode for organic EL displays provided with a novel Al alloy reflective film capable of securing a reflectance.

The reflective anode electrode for an organic EL display according to the present invention for solving the above problem includes a laminate structure including an Al-Ge-based alloy film and an oxide conductive film in contact with the Al-Ge-based alloy film, and the Al- It is a reflective anode electrode for an organic EL display in which a layer containing aluminum oxide as a main component is interposed at the contact interface between the Ge-based alloy film and the oxide conductive film, and the Al-Ge-based alloy film contains 0.1 to 2.5 atomic% of Ge. , Ge enriched layer and Ge-containing precipitate are formed at the contact interface between the Al-Ge-based alloy film and the oxide conductive film, and within 50 nm from the surface of the Al-Ge-based alloy film on the side of the oxide conductive film. It is characterized in that the average Ge concentration is at least twice the average Ge concentration in the Al-Ge-based alloy film, and the average diameter of the Ge-containing precipitate is at least 0.1 µm.

In a preferred embodiment of the present invention, the Al-Ge alloy film further contains Cu: 0.05 to 2.0 atomic%.

In a preferred embodiment of the present invention, the Al-Ge alloy film further contains a rare earth element: 0.2 to 0.5 atomic%.

In a preferred embodiment of the present invention, the oxide conductive film has a thickness of 5 to 30 nm.

In a preferred embodiment of the present invention, the Al-Ge-based alloy film is formed by sputtering or vacuum evaporation.

In a preferred embodiment of the present invention, the Al-Ge-based alloy film is electrically connected to the source/drain electrodes of the thin film transistor.

In addition, the present invention also includes a thin film transistor substrate provided with any of the above reflective anode electrodes, and an organic EL display provided with the thin film transistor.

Further, in the present invention, it is a sputtering target for forming the Al-Ge-based alloy film according to any one of the above, and contains 0.1 to 2.5 atomic% of Ge; Alternatively, a sputtering target containing 0.1 to 2.5 atomic% Ge and containing at least one of Cu: 0.05 to 2.0 atomic% and rare earth elements: 0.2 to 0.5 atomic% is also included.

According to the reflective anode electrode for an organic EL display according to the present invention, an Al-Ge-based alloy film containing a predetermined amount of Ge is used as a reflective film, and a Ge enriched layer and a Ge-enriched layer at the contact interface between the Al-Ge-based alloy film and the oxide conductive film are provided. Since Ge-containing precipitates are formed, and the average Ge concentration within 50 nm from the surface of the oxide conductive film side in the Al-Ge-based alloy film and the average diameter of the Ge-containing precipitates satisfy predetermined requirements, ITO or Even when direct contact with an oxide conductive film such as IZO, the electrical resistivity of the Al alloy reflective film itself can be kept low, while low contact resistance and high reflectivity can be ensured.

In addition, when the reflective anode electrode according to the present invention is used, current can be efficiently flowed through the organic light-emitting layer, and light emitted from the organic light-emitting layer can be efficiently reflected by the reflective film, so that an organic EL display having excellent luminance can be obtained. Can be realized.

1 is a schematic diagram showing an organic EL display including a reflective anode electrode according to an embodiment of the present invention.
Fig. 2 is a diagram showing a Kelvin pattern used for measuring contact resistance between an Al alloy reflective film and an oxide conductive film.
3A is a graph showing the current-voltage characteristics of the reflective anode electrode according to Test No. 6 of the Example (an example in which the conductivity is ensured: Ohmic).
3B is a graph showing the current-voltage characteristics of the reflective anode electrode according to Test No. 2 of the Example (an example in which conduction is not secured: non-ohm).
4A is an example of a Ge enriched layer formed at the contact interface between an ITO film constituting an oxide conductive film (transparent conductive film) and an Al-0.6 Ni-0.5 Cu-0.35 La-1.0 Ge (unit: atomic%) alloy film ( It is a cross-sectional TEM photograph showing Test No. 6) of Examples.
Fig. 4B is a diagram showing the results of the semi-quantitative EDX of Test No. 6 of the Example (points indicate points in the TEM photograph of Fig. 4A).
5A is a diagram showing the results of EDX analysis of the chemical composition of point 1-1 in FIG. 4A.
5B is a diagram showing the results of EDX analysis of the chemical composition of points 1-2 in FIG. 4A.
5C is a diagram showing the results of EDX analysis of the chemical composition of points 1-3 in FIG. 4A.
5D is a diagram showing the results of EDX analysis of the chemical composition of points 1-4 in FIG. 4A.
5E is a diagram showing the results of EDX analysis of the chemical composition of points 1-5 in FIG. 4A.
Fig. 6 is a diagram showing the result of performing a composition analysis in the depth direction from the oxide conductive film to the Al alloy reflective film in Test No. 6 of the Example by XPS analysis. In addition, the horizontal axis in the figure represents the sputter depth (nm), and the vertical axis represents the atomic concentration (atomic %).
7 is a plan view SEM photograph showing Ge-containing precipitates formed at a contact interface between an Al-Ge-based alloy film and an oxide conductive film in Test No. 6 of Examples.

Hereinafter, an embodiment for carrying out the present invention (this embodiment) will be described in detail. In addition, the present invention is not limited to the embodiments described below, and can be carried out with arbitrary changes within the scope not departing from the gist of the present invention.

(Organic EL display)

First, an outline of an organic EL display using the reflective anode electrode of the present embodiment will be described using FIG. 1. In the following, the Al-Ge alloy, Al-Ge-Cu alloy, Al-Ge-X alloy, and Al-Ge-Cu-X alloy (wherein X is Ni or rare earth element) used in the present embodiment are incorporated. It may be represented by "Al-Ge-based alloy".

A TFT 2 and a passivation film 3 are formed on the substrate 1, and a planarization layer 4 is formed thereon. A contact hole 5 is formed on the TFT 2, and the source/drain electrode (not shown) of the TFT 2 and the Al-Ge-based alloy film 6 are electrically connected through the contact hole 5 .

The Al-Ge-based alloy film is preferably formed by a sputtering method. Preferred film forming conditions of the sputtering method are as follows.

Substrate temperature: 25°C or more, 200°C or less (more preferably 150°C or less)

Film thickness of the Al-Ge-based alloy film: 50 nm or more (more preferably 100 nm or more), 300 nm or less (more preferably 200 nm or less)

An oxide conductive film 7 is formed directly on the Al-Ge-based alloy film 6. The Al-Ge-based alloy film 6 and the oxide conductive film 7 act as a reflective electrode of an organic EL element, are electrically connected to the source and drain electrodes of the TFT 2, and act as an anode electrode. do. Therefore, the Al-Ge-based alloy film 6 and the oxide conductive film 7 constitute the reflective anode electrode of the present embodiment.

The oxide conductive film is preferably formed by a sputtering method. Preferred film forming conditions of the sputtering method are as follows.

Substrate temperature: 25°C or more, 150°C or less (more preferably 100°C or less)

Film thickness of oxide conductive film: 5 nm or more (more preferably 10 nm or more), 30 nm or less (more preferably 20 nm or less)

An organic light-emitting layer 8 is formed on the oxide conductive film 7 and a cathode electrode 9 is formed thereon. In such an organic EL display, since light emitted from the organic light emitting layer 8 is efficiently reflected by the reflective anode electrode of this embodiment, excellent light emission luminance can be realized. In addition, the higher the reflectance is, the better, and generally 75% or more, preferably 80% or more is required.

Here, in direct contact with the oxide conductive film on the Al-Ge-based alloy film which is a reflective film, the following method is preferably used.

After the Al-Ge-based alloy film → oxide conductive film is sequentially formed, heat treatment is performed at a temperature of 150°C or higher in a vacuum or inert gas (eg, nitrogen) atmosphere. In addition, in this specification, heat treatment of the reflective anode electrode (Al-Ge-based alloy film + oxide conductive film) after formation of the oxide conductive film is sometimes referred to as "post annealing".

Thereby, the transparency of the oxide conductive film is improved, the reflectance is improved, and formation of the Ge enriched layer and the Ge-containing precipitate described in detail below can be promoted. That is, by using the above method, reduction in electrical resistivity and increase in reflectance are expected.

Further, the atmosphere when the oxide conductive film is directly contacted on the Al-Ge-based alloy film may be continuously formed while maintaining the atmosphere before the contact, that is, an atmosphere of vacuum or an inert gas.

(Reflective anode electrode)

Subsequently, the reflective anode electrode of the present embodiment will be described. The present inventors have provided a novel Al alloy reflective film capable of securing low contact resistance and high reflectance while suppressing the electrical resistivity of the Al alloy reflective film itself even when the reflective film is directly in contact with an oxide conductive film such as ITO or IZO. In order to provide a reflective anode electrode for an organic EL display, intensive examination has been made.

As a result, a laminate structure including an Al-Ge-based alloy film and an oxide conductive film in contact with the Al-Ge-based alloy film was included, and aluminum oxide (Al ₂ O) was formed at the contact interface between the Al-Ge-based alloy film and the oxide conductive film. ₃ ) is a reflective anode electrode for organic EL displays with a layer as a main component interposed therebetween. The Al-Ge alloy film contains 0.1 to 2.5 atomic% Ge, and the contact interface between the Al-Ge alloy film and the oxide conductive film A Ge enriched layer and a Ge-containing precipitate are formed, and the average Ge concentration within 50 nm from the surface on the side of the oxide conductive film in the Al-Ge alloy film is 2 of the average Ge concentration in the Al-Ge alloy film. It has been found that the intended purpose is achieved by using a reflective anode electrode for organic EL displays having an average diameter of 0.1 µm or more of a Ge-containing precipitate having an average diameter of 0.1 µm or more.

In addition, in this specification, ``the electrical resistivity of the Al alloy reflective film itself is low'' means that the electrical resistivity is 7.0 μΩ·cm or less when the electrical resistivity of the Al alloy reflective film itself is measured by the method described in Examples to be described later. do.

In addition, in the present specification, "low contact resistance" means when the contact resistance is measured by the method described in the examples described later (a square contact hole having a side of 10 μm), the current is proportional to the voltage, and the contact resistance is approximately It means something constant (ohmic).

In addition, in the present specification, "high reflectance" means that the reflectance at 450 nm is 75% or more when the reflectance is measured by the method described in Examples described later.

The reason why good properties are obtained by using the Al-Ge-based alloy is unclear in detail, but at the contact interface between the Al-Ge-based alloy film and the oxide conductive film, a Ge enriched layer that prevents Al diffusion and a Ge-containing precipitate It is presumed that this is because the increase in contact resistance and decrease in reflectance are suppressed while suppressing the electrical resistivity of the Al alloy reflective film itself to be low.

Here, the "Ge enriched layer" means a region having an average Ge concentration higher than the average Ge concentration in the Al-Ge-based alloy film. In addition, the "Ge-containing precipitate" means a precipitate in which part or all of Ge is precipitated, and examples thereof include an intermetallic compound of Al and Ge.

Here, a layer (insulation layer) containing aluminum oxide as a main component is interposed at the contact interface between the Al-Ge-based alloy film and the oxide conductive film. Since Al is very susceptible to oxidation, it is easy to form aluminum oxide on the surface of the Al-Ge-based alloy film by bonding with oxygen in the atmosphere. In addition, when the Al-Ge-based alloy film and the oxide conductive film are brought into contact with each other, oxide conduction Al deprives oxygen from the film, and aluminum oxide tends to be formed at the interface thereof. Since this aluminum oxide-based layer is insulating, it causes an increase in the contact resistance between the Al-Ge-based alloy film and the oxide conductive film, but in this embodiment, in addition, the conductive Ge enriched layer and the Ge-containing precipitate Also formed, most of the contact current flows through the Ge enriched layer or Ge-containing precipitate. As a result, the Al-Ge-based alloy film and the oxide conductive film are electrically conductive, and an increase in contact resistance is suppressed. In addition, the main component refers to the most components, and the content is usually 70% by mass or more, preferably 90% by mass or more, and more preferably 99% by mass or more.

In order to effectively suppress the increase in the contact resistance, the average Ge concentration within 50 nm from the surface of the oxide conductive film side in the Al-Ge-based alloy film is in the Al-Ge-based alloy film (surface of the Al-Ge-based alloy film). It is preferable that it is 2 times or more of the average Ge concentration of the part exceeding 50 nm), it is more preferable that it is 2.5 times or more, and it is still more preferable that it is 3 times or more.

Similarly, in order to effectively suppress the increase in the contact resistance, the average diameter of the Ge-containing precipitate is preferably 0.1 µm or more, more preferably 0.15 µm or more, and even more preferably 0.2 µm or more.

The thickness of the Ge enriched layer is preferably 5 nm or more and 100 nm or less, and more preferably 10 nm or more and 80 nm or less.

The thickness in the Ge enriched layer, the depth from the surface of the Al-Ge-based alloy film, and the average diameter of the Ge-containing precipitate are cross-sectional TEM (magnification: 300,000 times) or planar SEM of the contact interface between the Al-Ge-based alloy film and the oxide conductive film. (Magnification: 30,000 times), etc. can be performed and measured. In addition, the "average Ge concentration within 50 nm from the surface of the Al-Ge-based alloy film" and "average Ge concentration in the Al-Ge-based alloy film" were determined by using the cross-sectional TEM observation sample, and using the EDX (Energy Dispersive X-ray, It can be measured by performing a chemical composition analysis by Sigma manufactured by KEVEV). TEM observation can be measured using "FE-TEM HF-2000" manufactured by Hitachi Seisakusho.

In the Ge-enriched layer and the Ge-containing precipitate, during film formation or in a heat treatment process, Ge of an Al-Ge-based alloy having a solid solubility limit of almost 0 at room temperature is precipitated at the aluminum grain boundary, or a part thereof is diffusely concentrated on the aluminum surface. It is thought to be formed.

For example, the Ge-enriched layer and the Ge-containing precipitate are, as described above, after sequentially forming an Al-Ge-based alloy film → an oxide conductive film, and then in a vacuum or inert gas (for example, nitrogen) atmosphere, at a temperature of 150° C. or higher. It is formed when heat treatment is performed in (post annealing) or the like.

In order to effectively exhibit the effect of reducing the contact resistance due to the above-described Ge enriched layer or Ge-containing precipitate, it is necessary that the Ge content in the Al-Ge-based alloy film be 0.1 atomic% or more. This is because when the Ge content is less than 0.1 atomic%, a Ge enriched layer or a Ge-containing precipitate such that the contact resistance with the oxide conductive film is reduced is not sufficiently obtained, and the above action is not exhibited effectively.

On the other hand, in order to effectively exhibit the effect of improving the reflectance due to the Ge enriched layer or the Ge-containing precipitate, it is necessary that the Ge content in the Al-Ge-based alloy film is 2.5 atomic% or less. This is because when the Ge content exceeds 2.5 atomic%, the electric resistivity of the Al alloy reflective film itself cannot be suppressed low. In addition, this is because the reflectance is lowered due to excessive formation of the Ge-enriched layer or the Ge-containing precipitate, and the above action may not be exhibited effectively. In addition, this is because convex portions (hills) are generated on the surface after heat treatment, which causes a short circuit of the element.

The Ge content is preferably 0.15 atomic% or more, more preferably 0.20 atomic% or more, preferably 1.5 atomic% or less, more preferably 1.0 atomic% or less. In addition, the Al-Ge-based alloy film of this embodiment contains Ge, and the remainder is Al and unavoidable impurities. As an impurity element, specifically, oxygen, nitrogen, carbon, iron, etc. are mentioned. These elements are each regulated to 0.01 atomic% or less. In addition, if these elements are within this range, not only when contained as an inevitable impurity, but also when actively added, will not interfere with the effect of the present embodiment.

The Al-Ge-based alloy film may further contain 0.05 to 2.0 atomic% of Cu. By containing a predetermined amount of Cu, precipitates of Cu and Ge are formed.Since the oxide layer on the precipitate has higher conductivity than the oxide layer formed on Al, the contact resistance can be reduced while suppressing a decrease in reflectance. I can. If the Cu content is less than 0.05 atomic%, the amount of the precipitate is not sufficient, the effect is not exhibited effectively, and when the Cu content exceeds 2.0 atomic%, the precipitate is excessively formed, resulting in a reflectance. It decreases, and the said action is not exhibited effectively.

In addition, the Al-Ge-based alloy film further comprises 0.1 to at least one element selected from the group consisting of Ni and rare earth elements (La, Nd, etc.) (hereinafter, sometimes referred to as group X) in total from 0.1 to 1 element. It may contain 2.0 atomic%, whereby the heat resistance of the Al-Ge-based alloy film is improved, and not only the formation of hillocks is effectively prevented, but also the corrosion resistance to an alkali solution is improved. Elements belonging to group X may be added alone or in combination of two or more.

When the content of the element belonging to group X (in case of single, it is the total amount in case of using two or more types in combination) is less than 0.1 atomic%, both the heat resistance improvement effect and the alkali corrosion resistance improvement effect are effective. Can't be demonstrated. From the viewpoint of improving these properties only, the higher the content of the element belonging to group X is, the better, but when the amount exceeds 2 atomic%, the electrical resistivity of the Al-Ge-based alloy film itself increases. Therefore, the content of the element belonging to group X is preferably 0.1 atomic% or more (more preferably 0.2 atomic% or more), and preferably 2 atomic% or less (more preferably 0.8 atomic% or less). In addition, when a rare earth element (especially La) is used as an element belonging to group X, the content of the rare earth element is preferably 0.2 to 0.5 atomic%.

In addition, in order to effectively exhibit the above action by an element belonging to group X, when the total amount of the element is 1 atomic% or more, it is preferable that the element is present as a precipitate.

The oxide conductive film used in this embodiment is not particularly limited, and commonly used ones such as indium tin oxide (ITO) and indium zinc oxide (IZO) are mentioned, but indium tin oxide is preferable.

The preferred thickness of the oxide conductive film is 5 to 30 nm. If the thickness of the oxide conductive film is less than 5 nm, pinholes may be generated in the ITO film and cause dark spots. On the other hand, if the thickness of the oxide conductive film exceeds 30 nm, the reflectance decreases. A more preferable thickness of the oxide conductive film is 5 nm or more and 20 nm or less.

In addition to low contact resistance and excellent reflectance, the reflective anode electrode for an organic EL display of the present embodiment uses a general-purpose Ag-based alloy, as well as the work function of the upper oxide transparent conductive film in a laminated structure with an oxide transparent conductive film. Since it is controlled to the same degree as in the case, and preferably has excellent alkali corrosion resistance and heat resistance, it is preferable to apply this to a thin film transistor substrate and further to a display device (especially an organic EL display).

(Sputtering target)

The Al-Ge-based alloy film is preferably formed by a sputtering method or a vacuum evaporation method, and in particular, it is more preferably formed by a sputtering method using a sputtering target (hereinafter sometimes referred to as a "target"). This is because, according to the sputtering method, a thin film having excellent in-plane uniformity of components and film thickness can be formed more easily than a thin film formed by an ion plating method or an electron beam evaporation method.

In order to form the Al-Ge-based alloy film by the sputtering method, as the target, the above-described elements (Ge and, preferably, Cu, or elements of group X such as Ni or rare earth elements (La, Nd, etc.)) are used. As included, if an Al alloy sputtering target having the same composition as the desired Al-Ge-based alloy film is used, there is no fear of composition deviation, and an Al-Ge-based alloy film having a desired composition composition can be formed.

Accordingly, in the present embodiment, a sputtering target having the same composition as that of the Al-Ge-based alloy film described above is also included within the scope of the present embodiment. Specifically, the target contains 0.1 to 2.5 atomic% of Ge; Alternatively, Ge is contained in an amount of 0.1 to 2.5 atomic%, and at least one of Cu: 0.05 to 2.0 atomic% and a rare earth element: 0.2 to 0.5 atomic%, and the remainder is Al and unavoidable impurities.

The shape of the target includes those processed into arbitrary shapes (rectangular plate shape, circular plate shape, donut plate shape, etc.) according to the shape and structure of the sputtering device.

As a method for producing the target, a method obtained by manufacturing an ingot containing an Al-Ge-based alloy by a melt casting method, a powder sintering method, or a spray forming method, or a preform containing an Al-Ge-based alloy (to obtain a final dense body The method obtained by densifying the preform by densifying means after manufacturing the previous intermediate) is mentioned.

[Example]

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples, and it is also possible to carry out changes in a range suitable for the purpose, They are all included in the technical scope of the present invention.

In this example, various Al alloy reflective films were used to measure reflectance (after heat treatment), contact resistance between the Al alloy reflective film and the oxide conductive film, and electrical resistivity and heat resistance (with or without hillock) of the Al alloy reflective film.

Specifically, an alkali-free glass plate (plate thickness: 0.7 mm) was used as a substrate, and an Al-Ge-based alloy film (film thickness: 200 nm) as a reflective film was produced on the surface thereof by a sputtering method. The chemical composition of the Al-Ge-based alloy film is as shown in Table 1. In addition, film formation conditions were substrate temperature: 25°C, pressure: 0.26 MPa, power source: direct current, film formation power density: 5 to 20 W/cm ² . For comparison, a pure Al film (film thickness: about 100 nm) was similarly formed by sputtering. The chemical composition of the reflective film was identified by ICP (Inductively Coupled Plasma) emission analysis.

For each reflective film formed in the above manner, an ITO film was formed. Further, after the formation of the ITO film, heat treatment (post annealing) was performed at 250° C. for 60 minutes in a nitrogen atmosphere.

Here, in the formation of the ITO film, an Al-Ge-based alloy film was formed, once released to the atmosphere, an ITO film having a thickness of 10 nm was formed by sputtering, and a reflective anode electrode (reflective film + oxide conductive film) was formed. . The film formation conditions were: substrate temperature: 25°C, pressure: 0.8 mTorr, and DC power: 150 W.

For each reflective anode electrode fabricated as described above, (1) reflectance (after heat treatment), (2) contact resistance between the Al alloy reflective film and the oxide conductive film, (3) electrical resistivity of the Al alloy reflective film, and (4) heat resistance (Hilox Presence or absence of) was measured and evaluated as follows.

(1) Reflectance (after heat treatment, 450nm)

As for the reflectance, the spectral reflectance in the range of the measurement wavelength: 1000-250 nm was measured using the visible/ultraviolet spectrophotometer "V-570" made by Nippon Bunko. Specifically, the value obtained by measuring the height of the reflected light of the sample with respect to the intensity of the reflected light of the reference mirror was referred to as "reflectance". In addition, the reflectance was measured after the heat treatment (post annealing). A reflectance of 75% or more at 450 nm was evaluated as good, and a reflectance of less than 75% was evaluated as defective.

(2) Al alloy reflective film and oxide conductive film contact resistance

For evaluation of the contact resistance, the Kelvin pattern shown in Fig. 2 was used. For the Kelvin pattern, after forming the Al alloy reflective film, an In-Sn-O (Sn: 10 wt%) thin film (ITO film, film thickness: 10 nm) is then laminated to form a wiring pattern, and then on the surface thereof. A SiN film (film thickness: 200 nm) as a passivation film was formed by a plasma CVD (Chemical Vapor Deposition) device. Film formation conditions were substrate temperature: 280°C, gas ratio: SiH ₄ /NH ₃ /N ₂ =125/6/185, pressure: 137 MPa, and RF power: 100 W. After patterning the SiN film, a Mo film (film thickness: 100 nm) was formed on the surface thereof by sputtering, and the Mo film was patterned to obtain the Kelvin pattern in FIG. 2.

To measure the contact resistance, a Kelvin pattern shown in Fig. 2 (contact hole size: a square with a side of 10 μm) was prepared, and a four-terminal measurement (a current was passed through an Al\ITO-Mo alloy, and Al\ITO was used as a separate terminal). -Method of measuring the voltage drop between Mo alloys) was performed. Specifically, by flowing a current I between I ₁ -I _{2 in} FIG. 2 and monitoring the voltage V between V ₁ -V ₂ , the contact resistance R of the connection part C is set to [R = (V ₁ -V ₂ )/ It was obtained as I ₂ ]. That the current was proportional to the voltage and the contact resistance was substantially constant was regarded as good (evaluation: ○) as "ohmic". In addition, the fact that the current was not proportional to the voltage was referred to as "non-omic" as a defect (evaluation: x). In addition, as an example determined as "ohmic", a graph showing the current-voltage characteristics of the reflective anode electrode according to Test No. 6 of Example in FIG. 3A is further determined as "non-ohmic". In FIG. 3B A graph showing the current-voltage characteristics of the reflective anode electrode according to Test No. 2 of Example is shown.

(3) Electrical resistivity of Al alloy reflective film

The electrical resistivity of the Al alloy reflective film itself was measured by a four-terminal method using a Kelvin pattern. An electrical resistivity of 7.0 μΩ·cm or less was evaluated as good, and a value exceeding 7.0 μΩ·cm was evaluated as defective.

(4) Heat resistance (with or without hillock)

Heat resistance was judged by observing the surface of the reflective anode electrode after the heat treatment with an optical microscope (magnification: 1000 times). Specifically, in an arbitrary 140 µm x 100 µm area, those with less than 5 hillocks having a diameter of 1 µm or more were judged as "no hillocks" and evaluated as good. In addition, by the same evaluation, the thing having 5 or more hillocks was judged as "there is hillock", and it was evaluated as defective.

Table 1 shows these results.

In Table 1, Tests Nos. 4 to 7 and 9 to 12 are Examples, and Tests Nos. 1 to 3 and 8 are Comparative Examples. In each example using the Al alloy reflective film that satisfies the requirements of the present invention, in all items of reflectance, contact resistance, electrical resistivity, and heat resistance, good results were obtained, so it was considered as good (evaluation: ○) as a comprehensive evaluation. .

On the other hand, each comparative example did not satisfy any of the requirements specified in the present invention, and did not satisfy the performance of the electrical resistivity or contact resistance of the reflective film, so it was regarded as defective (evaluation: ×) as a comprehensive evaluation. Specifically, for Test Nos. 1 to 3, the contact resistance was "evaluation ×", and for Test No. 8, the electrical resistivity of the reflective film was "defective".

Subsequently, for the test examples corresponding to the examples, a Ge enriched layer and a Ge-containing precipitate were formed at the contact interface between the Al alloy reflective film and the oxide conductive film, and the average Ge concentration within 50 nm from the surface of the Al alloy reflective film. And in order to confirm whether the average diameter of the Ge-containing precipitate satisfies the above requirements, various analyzes such as cross-sectional TEM and EDX analysis were performed.

As an example, an ITO film constituting an oxide conductive film (transparent conductive film) and Al-0.6 Ni-0.5 Cu-0.35 La-1.0 Ge (unit: atomic%) in Test No. 6 corresponding to the Example A cross-sectional TEM photograph (magnification: 300,000 times) showing an example of a Ge enriched layer formed at the contact interface of the alloy film (Al alloy reflective film) is shown in Fig. 4A. In addition, the EDX semi-quantitative result (excluding carbon C, the concentration of each element is at%) at each point "1-1" to "1-5" in FIG. 4A is shown in FIG. 4B, and the composition of each point is The results of the EDX analysis are shown in Figs. 5A to 5E, respectively (in Figs. 5A to 5E, the vertical axis represents counts, and the horizontal axis represents energy).

In Fig. 4A, a region from the interface between the oxide conductive film and the Al alloy reflective film to a depth of about 50 nm is the Ge enriched layer. As shown in the result of Fig. 4B, the Ge concentrations at points 1-1 and 1-2 belonging to the Ge enriched layer were 2.7 at% and 3.0 at%, respectively (average 2.85 at%), but other than the Ge enriched layer Ge concentration at points 1-3 to 1-5 belonging to the region of (the bulk portion of the Al alloy reflective film deeper than about 50 nm from the interface between the oxide conductive film and the Al alloy reflective film) is 0.6 to 1.0 at% (average 0.8 at %). From this, it is understood that the average Ge concentration within 50 nm from the surface of the Al alloy reflective film is twice or more (2.85/0.8 = about 3.6 times) of the average Ge concentration in the Al alloy reflective film.

In addition, from the results of Fig. 4B, it can be seen that the O (oxygen) concentration at point 1-1 near the contact interface between the oxide conductive film and the Al alloy reflective film is 41.9 at%, which is higher than the O concentration at other points. . From this, it is suggested that at the contact interface between the Al alloy reflective film and the oxide conductive film, a layer mainly composed of aluminum oxide of several nm or so exists.

FIG. 6 is a diagram showing the results of a composition analysis in the depth direction from an oxide conductive film to an Al alloy reflective film in Test No. 6 by XPS (X-ray Photoelectron Spectroscopy) analysis. In addition, in the figure, the horizontal axis represents the sputter depth (nm) in terms of SiO ₂ , and the vertical axis represents the atomic concentration (atomic%). The specific measurement method is as follows. First, using the X-ray photoelectron spectroscopy apparatus Quantera SXM manufactured by Physical Electronics, a qualitative analysis was performed using the wide-area photoelectron spectrum of the outermost surface. Thereafter, etching was performed from the surface to the depth direction by Ar ⁺ sputtering, and narrow-band photoelectron spectra of the constituent elements of the film and the elements detected at the outermost surface were measured at each predetermined depth. The depth direction composition distribution (atomic%) was calculated from the area intensity ratio and the relative sensitivity coefficient of the narrow-band photoelectron spectrum obtained at each depth.

Measuring conditions

X-ray source: Al Kα (1486.6eV)

X-ray output: 25W

X-ray beam diameter: 100㎛

· Photoelectron extraction angle: 45°

Device: Quantera SXM

Ar ⁺ sputter conditions

Incident energy: 1keV

Raster: 2mm×2mm

Sputter rate: 1.83 nm/min (SiO ₂ conversion)

· The sputter depth is all the depth in terms of SiO ₂ .

In Fig. 6, it is suggested that it is a region of an oxide conductive film (ITO film) from the point that the In concentration is high up to about 5 nm of the sputtering depth. And, at a sputtering depth of 5 nm to about 15 nm, the In concentration decreases while the Al concentration increases, which is considered to be a region of the layer containing aluminum oxide as a main component. In addition, since the region deeper than about 15 nm in the sputtering depth is the Al alloy reflective film, and the Ge concentration is high in the sputtering depth of 15 nm to 20 nm, the result of XPS analysis also shows that the Ge-enriched layer is located at the contact interface between the Al alloy reflective film and the oxide conductive film. And Ge-containing precipitates are suggested. In addition, the sputtering depth in FIG. 6 is different from the actual thickness in the film direction in the laminated film of the oxide conductive film and the Al alloy reflective film, which is derived from the sputtering depth in terms of SiO ₂ and the sputtering cross section.

7 is a plan view SEM photograph (magnification: 30,000 times) showing a Ge-containing precipitate formed at a contact interface between an Al-Ge-based alloy film and an oxide conductive film in Test No. 6. In addition, FIG. 7 shows the vicinity of point 1-1 or point 1-2 in FIG. 4A. As shown in Fig. 7, Ge-containing precipitates having a diameter of 0.1 µm or more can be confirmed in the area surrounded by broken lines.

From the above, for Test No.6, a Ge enriched layer and a Ge-containing precipitate were formed at the contact interface between the Al alloy reflective film and the oxide conductive film, and the average Ge concentration within 50 nm from the surface of the Al alloy reflective film and the corresponding Ge It was confirmed that the average diameter of the contained precipitate satisfies the above requirements. In addition, in Examples other than Test No. 6, it was confirmed that the above requirements were satisfied, similarly to the results of Test No. 6.

1: substrate
2: TFT
3: passivation film
4: planarization layer
5: contact hole
6: Al-Ge alloy film
7: oxide conductive film
8: organic light emitting layer
9: cathode electrode

Claims (8)

A laminated structure comprising an Al-Ge-based alloy film and an oxide conductive film in contact with the Al-Ge-based alloy film, and 70% by mass of aluminum oxide at a contact interface between the Al-Ge-based alloy film and the oxide conductive film. It is a reflective anode electrode for an organic EL display interposed with the layer containing above,
The Al-Ge-based alloy film contains 0.1 to 2.5 atomic% of Ge,
At the contact interface between the Al-Ge-based alloy film and the oxide conductive film, a Ge enriched layer and a Ge-containing precipitate are formed,
In the Al-Ge-based alloy film, the average Ge concentration from the surface of the oxide conductive film side to 50 nm is at least twice the average Ge concentration in the Al-Ge-based alloy film, and the Ge-containing precipitate Characterized in that the average diameter is 0.1㎛ or more
Reflective anode electrode for organic EL displays. The method of claim 1,
The said Al-Ge-based alloy film further contains Cu: 0.05 to 2.0 atomic%. The method of claim 1,
The Al-Ge-based alloy film further contains a rare earth element: 0.2 to 0.5 atomic%. The method of claim 1,
The reflective anode electrode, wherein the Al-Ge-based alloy film is electrically connected to a source/drain electrode of a thin film transistor. The method of claim 1,
The reflective anode electrode, characterized in that the Al-Ge-based alloy film is formed by a sputtering method or a vacuum deposition method. A thin film transistor substrate provided with the reflective anode electrode according to any one of claims 1 to 3. An organic EL display provided with the thin film transistor substrate according to claim 6. It is a sputtering target for forming the Al-Ge-based alloy film according to any one of claims 1 to 3,
Contains 0.1 to 2.5 atomic% Ge; Or, it contains 0.1 to 2.5 atomic% of Ge, and,
Cu: 0.05 to 2.0 atomic% and rare earth elements: 0.2 to 0.5 atomic%
A sputtering target characterized by containing at least one.

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