JP2019135694A - Reflective anode electrode for organic EL display - Google Patents

Abstract

To provide a reflective anode electrode for organic EL display comprising a novel Al alloy reflective film capable of securing low contact resistance and high reflectivity even in a case where the Al alloy reflective film is brought into direct contact with an oxide conductive film such as ITO or IZO.SOLUTION: The present invention relates to a reflective anode electrode for organic EL display consisting of 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 interposing a layer containing aluminium oxide as a main component on a contact interface thereof. The Al-Ge-based alloy film contains Ge in 0.1-2.5 atom%, and a Ge concentrated layer and a Ge containing deposit are formed on the contact interface of the Al-Ge-based alloy film and the oxide conductive film. In the Al-Ge-based alloy film, an average Ge concentration within 50 nm from a surface closer to the oxide conductive film is twice or more as much as an average Ge concentration in the Al-Ge-based alloy film, and an average diameter of the Ge containing deposit is 0.1 μm or more.SELECTED DRAWING: Figure 1

Description

  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 (particularly, a top emission type).

  An organic EL (Organic Electro-Luminescence) display, which is one of self-luminous flat panel displays, is an all-solid-type display that is formed by arranging organic EL elements in a matrix on a substrate such as a glass plate. It is a flat panel 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 volts to the organic EL element from the outside and passing a current, the organic molecules are pushed up to an excited state, and when the energy returns to the original ground state (stable state), the extra energy is used as light. discharge. This emission color is unique to organic materials.

  Organic EL elements are self-emitting and current-driven elements, and there are passive and active driving methods. The passive type has a simple structure, but full color is difficult. On the other hand, the active type can be increased in size and is suitable for full color, but the active type requires a thin film transistor (TFT) substrate. Note that a low-temperature polycrystalline Si (p-Si) or amorphous Si (a-Si) TFT is used for this TFT substrate.

  In the case of this active organic EL display, a plurality of TFTs and wirings become obstacles, and the area that can be used for the organic EL pixel is reduced. As the drive circuit becomes complicated and the number of TFTs increases, the effect becomes even greater. Recently, attention has been focused on a method for improving the aperture ratio by adopting a structure (top emission) in which light is extracted from the upper surface side instead of extracting light from a glass substrate.

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

  The anode electrode used in such an active matrix type top emission organic EL display is represented by ITO or IZO (Indium Zinc Oxide) for the purpose of reflecting light emitted from the organic EL element. The transparent oxide conductive film and the reflective film are laminated (reflective anode electrode). The reflective film used in the 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 an Ag alloy film 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 component is useful because of its high reflectance. Note that the Ag-based alloy has a specific problem that it is inferior in corrosion resistance, but the above 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 there is a problem that it is difficult to increase the size of a sputtering target necessary for film formation, an Ag-based alloy film is used as an active matrix type top emission organic EL display reflection film for a large TV. It is difficult to apply.

  On the other hand, if only the reflectance is taken into account, Al is also a good reflective film. For example, Patent Document 1 discloses an Al film or an Al—Nd film as a reflective film, and describes that an Al—Nd film is excellent in reflectance and desirable.

  However, when the Al reflective film is brought into direct contact with an oxide conductive film such as ITO or IZO, the contact resistance (contact resistance) is high, and a current sufficient for injecting holes into the organic EL element cannot be supplied. . In order to avoid this, a refractory metal such as Mo or Cr instead of Al is used for the reflective film, or a refractory metal such as Mo or Cr is provided as a barrier metal between the Al reflective film and the oxide conductive film. As a result, the reflectance is greatly deteriorated, resulting in a decrease in light emission luminance, which is a display characteristic.

  Therefore, Patent Document 2 proposes an Al—Ni alloy film containing 0.1 to 2 atomic% of Ni as a reflective electrode (reflective film) that can omit the barrier metal. According to this, it has a reflectance as high as that of pure Al, and a low contact resistance can be realized even if the Al reflective film is brought into direct contact with an oxide conductive film such as ITO or IZO.

  Similarly to Patent Document 2, as a reflective electrode (reflective film) in which the barrier metal can be omitted, Patent Document 3 proposes an Al—Ag alloy film containing 0.1 to 6 atomic% of Ag. Alternatively, in Patent Document 4, an Al—Ge— (Gd, La) alloy containing 0.05 to 0.5 atomic percent of Ge and 0.05 to 0.45 atomic percent of Gd and / or La in total. Membranes have been proposed.

JP 2005-259695 A JP 2008-122941 A JP 2011-108459 A JP 2008-160058 A

By the way, when an Al alloy is used as an anode electrode in a top emission type organic EL display, an insulating oxide film (a layer mainly composed of aluminum oxide) inevitably formed on the Al alloy surface in an oxygen-existing atmosphere. For this reason, there is a problem that current is difficult to flow. In this case, if a current of a predetermined value or more is attempted to flow, the voltage value necessary for the current to flow increases. Therefore, there is a problem that the power consumption increases when the same light emission intensity is maintained.
Further, as a characteristic required for the anode electrode, it can be mentioned that the electrical resistivity of the Al alloy reflecting film itself constituting the anode electrode is low.

  The present invention has been made in view of the above circumstances, and its purpose is to reduce the electrical resistivity of the Al alloy reflective film itself even when the Al alloy reflective film is brought into direct contact with an oxide conductive film such as ITO or IZO. An object of the present invention is to provide a reflective anode electrode for an organic EL display provided with a novel Al alloy reflective film that can ensure low contact resistance and high reflectance while keeping it low.

  A reflective anode for an organic EL display according to the present invention that solves the above-mentioned problems has a laminated structure including an Al—Ge-based alloy film and an oxide conductive film in contact with the Al-Ge-based alloy film. A reflective anode electrode for an organic EL display in which a layer mainly composed of aluminum oxide is interposed at a contact interface between an Al—Ge based alloy film and the oxide conductive film, wherein the Al—Ge based alloy film is a Ge In addition, a Ge-concentrated layer and a Ge-containing precipitate are formed at the contact interface between the Al—Ge alloy film and the oxide conductive film. The average Ge concentration within 50 nm from the surface on the oxide conductive film side in the Al—Ge alloy film is at least twice the average Ge concentration in the Al—Ge alloy film, and the Ge-containing precipitation Average of things Diameter and wherein the at 0.1μm or more.

  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 preferable embodiment of this invention, the film thickness of the said oxide electrically conductive film is 5-30 nm.

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

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

  The present invention also includes a thin film transistor substrate provided with any of the above-described reflective anodes, and an organic EL display provided with the thin film transistor.

  Furthermore, the present invention provides a sputtering target for forming the Al—Ge alloy film according to any one of the above, and contains 0.1 to 2.5 atomic% of Ge; Also included is a sputtering target containing 0.1 to 2.5 atomic% and containing at least one of Cu: 0.05 to 2.0 atomic% and rare earth element: 0.2 to 0.5 atomic%. .

According to the reflective anode electrode for an organic EL display according to the present invention, an Al—Ge alloy film containing a predetermined amount of Ge is used as a reflective film, and the contact interface between the Al—Ge alloy film and the oxide conductive film is used. A Ge-enriched layer and a Ge-containing precipitate are formed on the Al-Ge-based alloy film, and the average Ge concentration within 50 nm from the surface on the oxide conductive film side and the average diameter of the Ge-containing precipitate In order to satisfy the prescribed requirements, even if it is in direct contact with an oxide conductive film such as ITO or IZO, the electrical resistivity of the Al alloy reflective film itself is kept low, while ensuring low contact resistance and high reflectance. Can do.
In addition, if the reflective anode electrode according to the present invention is used, it is possible to efficiently pass a current through the organic light emitting layer, and further, the light emitted from the organic light emitting layer can be efficiently reflected by the reflective film. An organic EL display can be realized.

FIG. 1 is a schematic view 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 the contact resistance between the Al alloy reflective film and the oxide conductive film. FIG. 3A shows test no. 6 is a graph showing current-voltage characteristics of the reflective anode electrode according to 6 (an example in which conductivity is ensured: ohmic). FIG. 3B shows test No. of the example. 2 is a graph showing current-voltage characteristics of a reflective anode electrode according to No. 2 (example in which conductivity cannot be ensured: non-ohmic). FIG. 4A shows a contact interface between an ITO film constituting an oxide conductive film (transparent conductive film) and an Al-0.6Ni-0.5Cu-0.35La-1.0Ge (unit: atomic%) alloy film. It is a cross-sectional TEM photograph which shows the example (Test No. 6 of an Example) of the formed Ge concentrated layer. FIG. 4B shows test No. of the example. It is a figure which shows the EDX semi-quantitative result of 6 (a point shows each point in the TEM photograph of FIG. 4A). FIG. 5A is a diagram showing the result of EDX analysis of the chemical composition of point 1-1 in FIG. 4A. FIG. 5B is a diagram showing the result of EDX analysis of the chemical composition at point 1-2 in FIG. 4A. FIG. 5C is a diagram showing the result of EDX analysis of the chemical composition at point 1-3 in FIG. 4A. FIG. 5D is a diagram showing a result of EDX analysis of the chemical composition at point 1-4 in FIG. 4A. FIG. 5E is a diagram showing the result of EDX analysis of the chemical composition at point 1-5 in FIG. 4A. FIG. 6 shows the test No. of the example by XPS analysis. 6 is a diagram showing a result of composition analysis in a depth direction from an oxide conductive film to an Al alloy reflective film in FIG. In the figure, the horizontal axis indicates the sputtering depth (nm), and the vertical axis indicates the atomic concentration (atomic%). FIG. 7 shows the test No. of the example. 6 is a planar SEM photograph showing a Ge-containing precipitate formed at a contact interface between an Al—Ge alloy film and an oxide conductive film in FIG.

  Hereinafter, a mode for carrying out the present invention (the present embodiment) will be described in detail. In addition, this invention is not limited to embodiment described below, In the range which does not deviate from the summary of this invention, it can change arbitrarily and can implement.

(Organic EL display)
First, an outline of an organic EL display using the reflective anode electrode of the present embodiment will be described with reference to FIG. Hereinafter, the Al—Ge alloy, Al—Ge—Cu alloy, Al—Ge—X alloy, and Al—Ge—Cu—X alloy (where X is Ni or a rare earth element) used in the present embodiment are collectively shown. The “Al—Ge alloy” may be used as a representative.

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

The Al—Ge alloy film is preferably formed by sputtering. The preferable film forming conditions for the sputtering method are as follows.
Substrate temperature: 25 ° C. or higher and 200 ° C. or lower (more preferably 150 ° C. or lower)
Film thickness of Al—Ge 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 immediately above the Al—Ge alloy film 6. The Al—Ge alloy film 6 and the oxide conductive film 7 function as a reflective electrode of the organic EL element, and are electrically connected to the source / drain electrodes of the TFT 2 and function as an anode electrode. Therefore, the Al—Ge alloy film 6 and the oxide conductive film 7 constitute the reflective anode electrode of this embodiment.

The oxide conductive film is preferably formed by a sputtering method. The preferable film forming conditions for the sputtering method are as follows.
Substrate temperature: 25 ° C. or higher and 150 ° C. or lower (more preferably 100 ° C. or lower)
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 further formed thereon. In such an organic EL display, light emitted from the organic light emitting layer 8 is efficiently reflected by the reflective anode electrode of the present embodiment, so that excellent light emission luminance can be realized. The higher the reflectivity, the better. Generally, a reflectivity of 75% or more, preferably 80% or more is required.

Here, the following method is preferably used for bringing the oxide conductive film into direct contact with the Al—Ge-based alloy film, which is a reflective film.
After sequentially forming an Al—Ge-based alloy film → an oxide conductive film, heat treatment is performed at a temperature of 150 ° C. or higher in a vacuum or an inert gas (for example, nitrogen) atmosphere. Note that in this specification, heat treatment of the reflective anode electrode (Al—Ge alloy film + oxide conductive film) after the formation of the oxide conductive film may be referred to as “post-annealing”.

  Thereby, the transparency of the oxide conductive film is improved, the reflectance is improved, and the formation of the Ge-concentrated layer and the Ge-containing precipitate described in detail below can be promoted. That is, the use of the above method is expected to reduce the electrical resistivity and increase the reflectance.

  Note that the atmosphere when the oxide conductive film is brought into direct contact with the Al—Ge-based alloy film may be continuously formed while maintaining the atmosphere before the contact, that is, the atmosphere of a vacuum or an inert gas. Good.

(Reflective anode electrode)
Then, the reflective anode electrode of this embodiment is demonstrated. The present inventors secure low contact resistance and high reflectivity while keeping the electrical resistivity of the Al alloy reflective film low even when the reflective film is in direct contact with an oxide conductive film such as ITO or IZO. In order to provide a reflective anode electrode for an organic EL display equipped with a novel Al alloy reflective film, the inventors have intensively studied.

As a result, it has a laminated structure including an Al—Ge based alloy film and an oxide conductive film in contact with the Al—Ge based alloy film, and aluminum oxide is formed at the contact interface between the Al—Ge based alloy film and the oxide conductive film. A reflective anode electrode for an organic EL display in which a layer mainly composed of (Al ₂ O ₃ ) is interposed, and the Al—Ge-based alloy film contains 0.1 to 2.5 atomic% of Ge, A Ge concentrated layer and a Ge-containing precipitate are formed at the contact interface between the Al—Ge alloy film and the oxide conductive film, and 50 nm from the surface on the oxide conductive film side in the Al—Ge alloy film. A reflective anode electrode for an organic EL display in which the average Ge concentration is within twice the average Ge concentration in the Al—Ge alloy film and the average diameter of the Ge-containing precipitates is 0.1 μm or more. By using It was found that the purpose of is achieved.

  In this specification, “the electrical resistivity of the Al alloy reflective film itself is low” means that the electrical resistivity is 7 when the electrical resistivity of the Al alloy reflective film itself is measured by the method described in Examples below. Meaning less than 0.0μΩ · cm.

  Further, in this specification, “low contact resistance” means that when the contact resistance is measured by the method described in Examples (10 μm square contact hole), the current is proportional to the voltage and the contact resistance is substantially constant. It means what is (ohmic).

  Further, 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 characteristics can be obtained by using the above Al-Ge-based alloy is unknown in detail, but Al diffusion is caused at the contact interface between the Al-Ge-based alloy film and the oxide conductive film. It is presumed that a Ge-enriched layer and a Ge-containing precipitate are formed, thereby preventing an increase in contact resistance and a decrease in reflectance while keeping the electrical resistivity of the Al alloy reflective film itself 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. The “Ge-containing precipitate” means a precipitate in which a part or all of Ge is precipitated, and examples thereof include an intermetallic compound of Al and Ge.

  Here, a layer (insulator layer) containing aluminum oxide as a main component is interposed at the contact interface between the Al—Ge alloy film and the oxide conductive film. Since Al is very easily oxidized, aluminum oxide is easily formed on the surface of the Al—Ge based alloy film by combining with oxygen in the atmosphere, and the Al—Ge based alloy film and the oxide conductive film are brought into contact with each other. In some cases, Al takes oxygen from the oxide conductive film, and aluminum oxide is easily formed at the interface. Since the layer mainly composed of aluminum oxide is insulative, the contact resistance between the Al-Ge-based alloy film and the oxide conductive film is increased. Since a Ge concentrated layer and a Ge-containing precipitate having a property are also formed, most of the contact current flows through the Ge concentrated layer and the Ge-containing precipitate. As a result, the Al—Ge-based alloy film and the oxide conductive film become electrically conductive, and an increase in contact resistance is suppressed. The main component means the most abundant component, and 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 on the oxide conductive film side in the Al—Ge based alloy film is reduced in the Al—Ge based alloy film (Al—Ge It is preferable that the average Ge concentration of a part exceeding 50 nm from the surface of the alloy film is preferably 2 times or more, more preferably 2.5 times or more, and still more preferably 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 More preferably, it is 2 μm or more.

  The thickness of the Ge concentrated 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 of 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 the cross-section of the contact interface between the Al-Ge-based alloy film and the oxide conductive film. Measurement can be performed by TEM (magnification: 300,000 times), planar SEM (magnification: 30,000 times), or the like. 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” are obtained by using the above-mentioned cross-sectional TEM observation sample, EDX (Energy Dispersive X- ray, Sigma manufactured by KEVEV) and can be measured by conducting a chemical composition analysis. The TEM observation can be measured using “FE-TEM HF-2000” manufactured by Hitachi, Ltd.

  In the Ge-enriched layer and the Ge-containing precipitate, the Ge—Al—Ge-based alloy having a Ge solid solubility limit of approximately 0 at room temperature at the time of film formation or heat treatment, etc., precipitates at the aluminum grain boundary, It is thought that a part of it is formed by diffusion concentration on the aluminum surface.

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

  In order to effectively exert the contact resistance reducing action by the Ge-enriched layer and the Ge-containing precipitate described above, the Ge content in the Al—Ge-based alloy film is 0.1 atomic% or more. is necessary. If the Ge content is less than 0.1 atomic%, a Ge-concentrated layer and Ge-containing precipitates that reduce the contact resistance with the oxide conductive film cannot be obtained sufficiently, and the above-described effects are not effectively exhibited. is there.

  On the other hand, the Ge content in the Al—Ge alloy film should be 2.5 atomic% or less in order to effectively exhibit the effect of improving the reflectivity by the Ge concentrated layer or the Ge-containing precipitate. is necessary. This is because when the Ge content exceeds 2.5 atomic%, the electrical resistivity of the Al alloy reflective film itself cannot be kept low. Moreover, it is because there exists a possibility that a reflectance may fall and the said effect | action may not be exhibited effectively, when Ge concentration layer and Ge containing precipitate are formed excessively. In addition, convex portions (hillocks) are generated on the surface after the 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. Moreover, the Al—Ge-based alloy film of the present embodiment contains Ge, and the balance is Al and inevitable impurities. Specific examples of the impurity element include oxygen, nitrogen, carbon, and iron. Each of these elements is restricted to 0.01 atomic% or less. Moreover, if these elements are within this range, the effects of the present embodiment are not hindered not only when they are contained as inevitable impurities but also when they are actively added.

  The Al—Ge 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 this precipitate has higher conductivity than the oxide layer formed on Al, the reflectivity is high. The contact resistance can be reduced while suppressing the decrease in the resistance. When the Cu content is less than 0.05 atomic%, the amount of the precipitate is not sufficient, and the above effect is not exhibited effectively. When the Cu content exceeds 2.0 atomic%, the precipitation When the object is excessively formed, the reflectance is lowered, and the above-described effect is not effectively exhibited.

  The Al—Ge-based alloy film further includes 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. It may be contained in an amount of 0.1 to 2.0 atomic%, which not only improves the heat resistance of the Al-Ge alloy film and effectively prevents the generation of hillocks, but also improves the corrosion resistance to alkaline solutions. To do. The 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 (single amount when used alone, or total amount when two or more types are used in combination) is less than 0.1 atomic%, the heat resistance improving effect and the resistance Both of the effects of improving alkali corrosion cannot be effectively exhibited. From the standpoint of improving these characteristics alone, it is better that the content of the element belonging to Group X is larger. However, if the amount exceeds 2 atomic%, the electrical resistivity of the Al—Ge alloy film itself increases. Resulting in. Therefore, the content of the element belonging to Group X is preferably 0.1 atomic% or more (more preferably 0.2 atomic% or more), preferably 2 atomic% or less (more preferably 0.8 atomic% or less). ). In addition, when using rare earth elements (especially La) as an element which belongs to X group, it is preferable that content of rare earth elements is 0.2-0.5 atomic%.

  Further, in order to effectively exert the above-described action by the element belonging to Group X, it is preferable that the element is present as a precipitate when the total amount of the element is 1 atomic% or more.

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

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

  In addition to the low contact resistance and excellent reflectance, the reflective anode electrode for the organic EL display of the present embodiment also has a work function of the upper oxide transparent conductive film when a laminated structure with the oxide transparent conductive film is used. It is controlled to the same level as when using a general-purpose Ag-based alloy, and preferably has excellent alkali corrosion resistance and heat resistance, so it is applied to thin film transistor substrates and display devices (especially organic EL displays). It is preferable to do.

(Sputtering target)
The Al—Ge-based alloy film is preferably formed by a sputtering method or a vacuum evaporation method, and more preferably formed by a sputtering method using a sputtering target (hereinafter sometimes referred to as “target”). This is because according to the sputtering method, it is possible to easily form a thin film having excellent in-plane uniformity of components and film thickness compared to 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, an X group element such as the above-described elements (Ge and preferably Cu, Ni, or rare earth elements (La, Nd, etc.)) is used. If an Al alloy sputtering target having the same composition as the desired Al—Ge alloy film is used, there is no risk of composition deviation and an Al—Ge alloy film having a desired component composition is formed. I can do it.

  Therefore, in the present embodiment, a sputtering target having the same composition as the Al—Ge alloy film described above is also included in the scope of the present embodiment. Specifically, the target contains 0.1 to 2.5 atomic percent of Ge; or contains 0.1 to 2.5 atomic percent of Ge, and Cu: 0.05 to 2.0. Atomic% and rare earth elements: At least one of 0.2 to 0.5 atomic% is contained, and the balance is Al and inevitable impurities.

  The shape of the target includes those processed into an arbitrary shape (such as a square plate shape, a circular plate shape, or a donut plate shape) according to the shape or structure of the sputtering apparatus.

  As a method for producing the above target, a method for producing an ingot made of an Al—Ge alloy by a melt casting method, a powder sintering method, or a spray forming method, or a preform made of an Al—Ge alloy (final (final) And an intermediate body before obtaining a dense body), and then the preform is densified by a densifying means.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples, and modifications are made within a range that can be adapted to the gist thereof. It is also possible to carry out and they are all included in the technical scope of the present invention.

  In this example, various Al alloy reflective films were used, and reflectivity (after heat treatment), contact resistance between the Al alloy reflective film and the oxide conductive film, electrical resistivity and heat resistance (presence of hillock) ) Was measured.

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 by a sputtering method. The chemical composition of the Al—Ge alloy film is as shown in Table 1. The film formation conditions were substrate temperature: 25 ° C., pressure: 0.26 MPa, power source: direct current, and 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.

  An ITO film was formed for each reflective film formed as described above. Further, after the ITO film was formed, heat treatment (post-annealing) was performed at 250 ° C. for 60 minutes in a nitrogen atmosphere.

  Here, in forming the ITO film, an Al—Ge alloy film is formed, and after being opened to the atmosphere, an ITO film having a thickness of 10 nm is formed by sputtering, and a reflective anode electrode (reflective film) is formed. + Oxide conductive film) was formed. The film forming conditions are: substrate temperature: 25 ° C., pressure: 0.8 mTorr, DC power: 150 W.

  About each reflective anode electrode produced as described above, (1) reflectivity (after heat treatment), (2) contact resistance between the Al alloy reflective film and the oxide conductive film, and (3) electrical resistivity of the Al alloy reflective film And (4) Heat resistance (with or without hillocks) was measured and evaluated as follows.

(1) Reflectance (450 nm after heat treatment)
The reflectance was measured by using a visible / ultraviolet spectrophotometer “V-570” manufactured by JASCO Corporation, and the spectral reflectance in the measurement wavelength range of 1000 to 250 nm was measured. Specifically, a value obtained by measuring the reflected light height of the sample with respect to the reflected light intensity of the reference mirror was defined as “reflectance”. The reflectance was measured after the heat treatment (post-annealing). A sample having a reflectance at 450 nm of 75% or more was evaluated as good, and a sample having a reflectance of less than 75% was evaluated as poor.

(2) Contact Resistance between Al Alloy Reflective Film and Oxide Conductive Film For the evaluation of contact resistance, the Kelvin pattern shown in FIG. 2 was used. After forming the Al alloy reflective film, the Kelvin pattern is formed by successively laminating an In—Sn—O (Sn: 10 wt%) thin film (ITO film, film thickness: 10 nm) to form a wiring pattern, A SiN film (film thickness: 200 nm) as a passivation film was formed on the surface by a plasma CVD (Chemical Vapor Deposition) apparatus. The film forming conditions are: substrate temperature: 280 ° C., gas ratio: SiH ₄ / NH ₃ / N ₂ = 125/6/185, pressure: 137 MPa, RF power: 100 W. After patterning the SiN film, a Mo film (film thickness: 100 nm) was further formed on the surface by sputtering, and the Mo film was further patterned to obtain the Kelvin pattern shown in FIG.

The contact resistance is measured by preparing the Kelvin pattern (contact hole size: 10 μm square) shown in FIG. 2 and measuring the four terminals (current is supplied to the Al \ ITO-Mo alloy and Al \ ITO-Mo alloy is used at another terminal). The method of measuring the voltage drop between the two was performed. Specifically, by passing a current I between I _{1 and} I ₂ in FIG. 2 and monitoring the voltage V between V _{1 and} V ₂ , the contact resistance R of the connection C is set to [R = (V ₁ − V ₂ ) / I ₂ ]. A sample in which the current is proportional to the voltage and the contact resistance is substantially constant was evaluated as “ohmic” as good (evaluation: ◯). In addition, the case where the current was not proportional to the voltage was determined as “non-ohmic” as defective (evaluation: x). As an example of determining “ohmic”, in FIG. As an example in which the graph showing the current-voltage characteristics of the reflective anode electrode according to FIG. 6 is determined as “non-ohmic”, in FIG. 2 is a graph showing current-voltage characteristics of a reflective anode electrode according to 2;

(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. A material having an electrical resistivity of 7.0 μΩ · cm or less was evaluated as good, and a material having an electrical resistivity higher than 7.0 μΩ · cm was evaluated as defective.

(4) Heat resistance (with or without hillocks)
The 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 any 140 μm × 100 μm area, less than 5 hillocks having a diameter of 1 μm or more were judged as “no hillocks” and evaluated as good. Further, by the same evaluation, those having 5 or more hillocks were judged to be “with hillocks” and evaluated as defective.

  These results are shown in Table 1.

  In Table 1, test no. 4-7 and 9-12 are examples, test no. 1-3 and 8 are comparative examples. In each example using an Al alloy reflective film that satisfies the requirements of the present invention, good results were obtained in all items of reflectance, contact resistance, electrical resistivity, and heat resistance, so that the overall evaluation was good ( Evaluation: ○).

  On the other hand, each comparative example does not satisfy any of the requirements defined in the present invention, and does not satisfy the performance of the electrical resistivity or contact resistance of the reflective film, and therefore is poor as a comprehensive evaluation (evaluation: x) It was. Specifically, Test No. 1 to 3, the contact resistance is “Evaluation ×”. For No. 8, the electrical resistivity of the reflective film was “bad”.

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

  As an example, test no. 6, an ITO film constituting an oxide conductive film (transparent conductive film), and an Al-0.6Ni-0.5Cu-0.35La-1.0Ge (unit: atomic%) alloy film (Al alloy reflective film) FIG. 4A shows a cross-sectional TEM photograph (magnification: 300,000 times) showing an example of the Ge-concentrated layer formed on the contact interface. Moreover, the EDX semi-quantitative result (the carbon C is excluded, 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 shown. The results of EDX analysis are shown in FIGS. 5A to 5E, respectively (the vertical axis in FIGS. 5A to 5E 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 a Ge concentrated layer. As shown in the results of FIG. 4B, the Ge concentrations at points 1-1 and 1-2 belonging to the Ge-enriched layer are 2.7 at% and 3.0 at%, respectively (average 2.85 at%). On the other hand, points 1-3 to 1-5 belonging to a region other than the Ge-enriched layer (the bulk portion of the Al alloy reflective film deeper than the depth of about 50 nm from the interface between the oxide conductive film and the Al alloy reflective film). It can be seen that the Ge concentration is 0.6 to 1.0 at% (average 0.8 at%). From this, the average Ge concentration within 50 nm from the surface of the Al alloy reflective film is at least twice the average Ge concentration in the Al alloy reflective film (2.85 / 0.8 = about 3.6 times). Is understood.

  4B, the O (oxygen) concentration at point 1-1 in the vicinity of 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. I can read. This suggests that a layer mainly composed of aluminum oxide having a thickness of about several nanometers exists at the contact interface between the Al alloy reflective film and the oxide conductive film.

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

Measurement conditions X-ray source: Al Kα (1486.6 eV)
・ X-ray output: 25W
・ X-ray beam diameter: 100 μm
-Photoelectron extraction angle: 45 °
・ Device: Quantera SXM
Ar ⁺ Sputtering conditions • Incident energy: 1 keV
・ Raster: 2mm x 2mm
Sputtering speed: 1.83 nm / min (SiO ₂ conversion)
・ All sputter depths are SiO ₂ equivalent.

In FIG. 6, since the In concentration is high up to a sputtering depth of about 5 nm, it is suggested that the region is an oxide conductive film (ITO film) region. At a sputter 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 a layer mainly composed of aluminum oxide. The region deeper than the sputter depth of about 15 nm is an Al alloy reflective film, and the Ge concentration is high at a sputter depth of 15 nm to 20 nm. This suggests that a Ge-enriched layer and a Ge-containing precipitate are formed at the contact interface. Note that the sputter 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. This is because the sputter depth is the SiO ₂ equivalent depth. It is derived from the existence and sputtering cross section.

  FIG. 6 is a planar SEM photograph (magnification: 30,000 times) showing the Ge-containing precipitate formed at the contact interface between the Al—Ge alloy film and the oxide conductive film in FIG. FIG. 7 shows the vicinity of point 1-1 and point 1-2 in FIG. 4A. As shown in FIG. 7, a Ge-containing precipitate having a diameter of 0.1 μm or more can be confirmed in the region surrounded by the broken line.

  Based on the above, test no. 6, a Ge-enriched layer and a Ge-containing precipitate are 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 Ge It was confirmed that the average diameter of the contained precipitates satisfied the above-mentioned requirements. In addition, Test No. In Examples other than 6, test no. Similar to the result of 6, it was confirmed that the above requirement was satisfied.

1 Substrate 2 TFT
DESCRIPTION OF SYMBOLS 3 Passivation film | membrane 4 Planarization layer 5 Contact hole 6 Al-Ge type alloy film 7 Oxide electrically conductive film 8 Organic light emitting layer 9 Cathode electrode

Claims (9)

It has a laminated structure comprising an Al—Ge alloy film and an oxide conductive film in contact with the Al—Ge alloy film, and aluminum oxide is formed at the contact interface between the Al—Ge alloy film and the oxide conductive film. A reflective anode electrode for an organic EL display in which a layer mainly composed of
The Al—Ge-based alloy film contains 0.1 to 2.5 atomic% of Ge,
At the contact interface between the Al-Ge alloy film and the oxide conductive film, a Ge concentrated layer and a Ge-containing precipitate are formed.
In the Al—Ge based alloy film, an average Ge concentration within 50 nm from the surface on the oxide conductive film side is at least twice the average Ge concentration in the Al—Ge based alloy film, and the Ge content A reflective anode electrode for an organic EL display, wherein an average diameter of the precipitate is 0.1 μm or more.   The reflective anode according to claim 1, wherein the Al—Ge alloy film further contains Cu: 0.05 to 2.0 atomic%.   The reflective anode according to claim 1, wherein the Al—Ge alloy film further contains a rare earth element: 0.2 to 0.5 atomic%.   The reflective anode electrode according to any one of claims 1 to 3, wherein the oxide conductive film has a thickness of 5 to 30 nm.   The reflective anode according to any one of claims 1 to 4, wherein the Al-Ge alloy film is formed by a sputtering method or a vacuum deposition method.   The reflective anode electrode according to claim 1, wherein the Al—Ge alloy film is electrically connected to a source / drain electrode of a thin film transistor.   A thin film transistor substrate comprising the reflective anode electrode according to claim 1.   An organic EL display comprising the thin film transistor substrate according to claim 7. A sputtering target for forming the Al-Ge-based alloy film according to any one of claims 1 to 6,
Contains 0.1 to 2.5 atomic percent of Ge; or contains 0.1 to 2.5 atomic percent of Ge, and Cu: 0.05 to 2.0 atomic percent and rare earth elements: 0.0. A sputtering target comprising at least one of 2 to 0.5 atomic%.

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