JP4625558B2 - Transparent conductive film, method for producing the same, and use thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low resistance transparent conductive film with improved surface flatness.
[0002]
[Prior art]
ITO (Indium Tin Oxide) thin film has characteristics such as high conductivity and high transmittance, and can be easily finely processed. Therefore, display electrodes for flat panel displays, resistive touch panels, solar cell window materials, It is used in a wide range of fields such as antistatic films, electromagnetic wave preventing films, antifogging films, and sensors.
[0003]
Such ITO thin film production methods can be broadly divided into chemical film formation methods such as spray pyrolysis and CVD, and physical film formation methods such as electron beam evaporation, ion plating, and sputtering. . Among these, sputtering is used in various fields because it is a film forming method that facilitates uniform film formation over a large area and provides a high-performance film.
[0004]
With the development of the information society in recent years, the technical level required for the flat panel display and the like is increasing. An inorganic Electro Luminescence (EL) panel applies a strong electric field of 10E8 V / cm to the light emitting layer through the transparent electrode 1 and the metal back electrode 4 to the light emitting layer 3 sandwiched between the insulating layers 2 as shown in FIG. It has a structure that emits light. It has excellent characteristics such as high visibility due to self-emission and resistance to vibration because it is all solid. The panel structure is an XY matrix structure composed of strip-shaped orthogonal transparent electrodes and back electrodes. For this reason, with the increase in size and definition of the panel, there is a demand for lowering the resistivity of the transparent conductive film used particularly for the transparent electrode.
[0005]
In order to reduce the resistivity of the ITO thin film and at the same time increase the transmittance, for example, JP-A 04-272612 matrixes indium oxide and tin oxide is 1 to 20% by weight, gallium oxide is 0.1 to 20%. Membranes containing weight percent have been proposed.
[0006]
Further, since a strong electric field of 10E8 v / cm is applied when the light emitting layer emits light, if there is a large uneven portion on the surface of the transparent electrode 1, electric field concentration occurs at this portion, and dielectric breakdown is likely to occur. Become. When dielectric breakdown occurs, display on the pixel portion becomes impossible and deterioration of display quality as a display is caused. Therefore, it is necessary to reduce unevenness on the surface of the electrode.
By the way, when the ITO thin film is formed at room temperature, an amorphous film can be obtained except for special conditions. However, to reduce the resistivity of the thin film, it is preferable to crystallize the film. The crystallization temperature of ITO is around 150 ° C. (depending on the film formation conditions), and it is necessary to form a film at a film formation temperature higher than this temperature in order to obtain a crystal film. However, when a crystalline ITO thin film is formed by sputtering, film protrusions and domain structures characteristic of the ITO thin film are formed.
[0007]
In general, when an ITO film is formed by sputtering, argon and oxygen are used as sputtering gases. The resistivity of the thin film obtained by changing the amount of oxygen in the gas changes, and shows a minimum value at a certain oxygen partial pressure value. And when it forms with the oxygen partial pressure value in which the resistivity of such a thin film shows the minimum value, the processus | protrusion and domain structure of the above-mentioned thin film surface become remarkable, and it will be a surface state with poor flatness. In the case of such a film, the maximum height difference (Z-max) of the surface unevenness at the film thickness of 200 nm may reach 100 nm.
[0008]
On the other hand, in order to pursue the flatness of the thin film, a method of forming an amorphous film by deviating from the optimum oxygen partial pressure value or lowering the substrate temperature during film formation can be considered. However, in any case, the resistivity increases although the flatness of the thin film is ensured.
[0009]
For this reason, it has been desired to develop a transparent conductive film that satisfies both flatness and low resistivity.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a transparent conductive film having a flat film surface and low resistivity, which is suitable for a large high-definition EL panel.
[0011]
[Means for Solving the Problems]
As a result of intensive studies on conductive metal oxides in which ITO is doped with different elements, the inventors have made the resistivity of the panel less than 250 μΩ · cm and Z-max / t less than 10%. It was found that a transparent conductive film with high reliability can be obtained even in an EL panel to which a strong electric field is applied in response to an increase in size and definition. In addition, the inventors have found that such a thin film can be achieved in an ITO thin film containing gallium as a dopant, thereby completing the present invention.
[0012]
That is, the present invention is composed of indium, tin, gallium and oxygen excluding inevitable impurities, gallium is contained in an atomic ratio of Ga / (In + Sn + Ga) in a ratio of 2% to 9%, and tin is Sn / (Sn + In). And a resistivity of 250 μΩ · cm or less and a Z-max / t (t: film thickness) of 10% or less. Is. The present invention also relates to a device comprising such a transparent conductive film. Further, the present invention is composed of indium, tin, gallium and oxygen excluding inevitable impurities, gallium is contained at a ratio of 2% to 9% by atomic ratio of Ga / (In + Sn + Ga), and tin is Sn / (Sn + In). Sputtering targets containing an atomic ratio of 10% to 14% are sputtered with a sputtering power in which rf is superimposed on dc, and has a resistivity of 250 μΩ · cm or less and a Z-Max / t of The present invention relates to a method for producing a transparent conductive film satisfying 10% or less.
[0013]
In the present invention, Z-max is a parameter that numerically represents the degree of unevenness on the surface of the material, and the difference in height between the highest peak and the lowest valley in the surface area. Means. As a measuring method thereof, measurement by an atomic force microscope (AFM) is common. The atomic force microscope is a device that measures the surface irregularities by moving a small lever close to the surface of the material and scanning it in an area in the vertical and horizontal directions, converting the deflection generated at that time into a height in the direction perpendicular to the sample surface. is there. In the present invention, the lever was measured by scanning an area of 3 μm × 3 μm using an atomic force microscope (trade name “SPI3700”) manufactured by Seiko Denshi Kogyo Co., Ltd.
[0014]
Hereinafter, the present invention will be described in detail.
[0015]
The thin film according to the present invention and the device comprising the thin film can be manufactured, for example, by the following method.
[0016]
First, a sputtering target for forming a thin film is manufactured. As a sintered body for use in a sputtering target, the sintered density of the obtained sintered body is preferably 95% or more. More preferably, it is 98% or more.
[0017]
If the sintered density is less than the above density, abnormal discharge is likely to occur during sputtering, and abnormally grown particles with splats generated at this time are formed, making it difficult to obtain a flat film.
[0018]
The relative density in the present invention and (D) shows the relative value to the theoretical density determined from the true density of the arithmetic mean of In ₂ O _3, SnO ₂ and Ga ₂ O ₃ (d). The theoretical density (d) obtained from the arithmetic mean is the target composition, when the mixing amounts of In ₂ O ₃ , SnO ₂ and Ga ₂ O ₃ powders are a, b and c (g), respectively. Using true density of 7.179, 6.95, 5.95 (g / cm ³ ), d = (a + b + c) / ((a / 7.179) + (b / 6.95) + (c / 5) .95)). When the measured density of the sintered body is d1, the relative density is
It is calculated by the formula: D = d1 / d × 100 (%).
[0019]
A sintered body having a sintered density of 95% or more can be produced, for example, by the following method.
[0020]
As the raw material powder, for example, indium oxide powder, tin oxide powder and gallium oxide powder are mixed. It is also possible to use tin oxide solid solution indium oxide powder instead of indium oxide powder and tin oxide powder. At this time, if the average particle size of the powder used is large, the density after sintering may not be sufficiently increased, and it may be difficult to obtain a sintered body having a relative density of 95% or more. It is desirable that it is 0.5 μm or less, more preferably 0.1 to 1.5 μm. The powder may be mixed by dry mixing or wet mixing using a ball mill or the like.
[0021]
Here, the mixing amount of tin oxide is preferably 5 to 20% in terms of an atomic ratio of Sn / (Sn + In). More preferably, it is 8-17%, More preferably, it is 10-14%. This is because when the ITO thin film is produced using the target of the present invention, the composition has the lowest resistivity of the film.
[0022]
The mixing amount of gallium oxide is preferably 2 to 9% in terms of an atomic ratio of Ga / (In + Sn + Ga). More preferably, it is 3-8%, More preferably, it is 4-7%. If the amount of gallium oxide added is less than the above range, the effect of flattening the thin film may be reduced, resulting in a film with large unevenness. If the amount exceeds this range, the resistivity may be too high.
[0023]
A binder or the like is added to the mixed powder obtained as described above, and is molded by a molding method such as a press method or a casting method to produce a molded body. In the case of producing a molded body by the pressing method, after a predetermined mold is filled with the mixed powder, pressing is performed at a pressure of 100 to 300 kg / cm ² using a powder pressing machine. When the moldability of the powder is poor, a binder such as paraffin or polyvinyl alcohol may be added as necessary.
[0024]
In the case of producing a molded body by a casting method, a binder, a dispersant, and ion-exchanged water are added to the ITO mixed powder and mixed by a ball mill or the like to prepare a slurry for producing a molded body. Subsequently, casting is performed using the obtained slurry. It is preferable to defoam the slurry before injecting the slurry into the mold. Defoaming may be performed, for example, by adding a polyalkylene glycol antifoaming agent to the slurry and performing defoaming treatment in a vacuum. Subsequently, the cast molding is dried.
[0025]
Next, the obtained compact is subjected to consolidation treatment such as cold isostatic pressing (CIP) as necessary. Here CIP pressure is sufficient for obtaining a consolidation effect 1 ton / cm ² or more, it is desirable that preferably is 2~5ton / cm ^2. Here, when the first molding is performed by a casting method, a binder removal treatment may be performed for the purpose of removing moisture remaining in the molded body after CIP and organic substances such as a binder. Even when the first molding is performed by the press method, it is desirable to perform the same debinding process when a binder is used during molding.
[0026]
The molded body thus obtained is put into a sintering furnace and sintered. As a sintering method, any method can be applied, but considering the cost of production facilities and the like, sintering in the atmosphere is desirable. However, it goes without saying that other conventionally known sintering methods such as a hot press (HP) method, a hot isostatic pressing (HIP) method and an oxygen pressure sintering method can be used. The sintering conditions can be selected as appropriate, but the sintering temperature is preferably 1450 to 1650 ° C. in order to obtain a sufficient density increasing effect and to suppress the evaporation of tin oxide. The atmosphere during sintering is preferably air or a pure oxygen atmosphere. The sintering time is preferably 5 hours or more, preferably 5 to 30 hours in order to obtain a sufficient density increasing effect. In this way, a gallium-containing ITO sintered body can be produced.
[0027]
Next, after processing the obtained sintered body into a desired shape, a sputtering target is manufactured by bonding to a backing plate made of oxygen-free copper, if necessary, using an indium half or the like.
[0028]
By using the obtained sputtering target, the transparent conductive thin film of the present invention can be obtained on a substrate such as a glass substrate or a film substrate. As a means for film formation, a sputtering method using 50 to 500 W of electric power with rf superimposed on dc (depending on the size of the cathode) is adopted to reduce the resistivity and flatten the thin film. It is preferable to do. At this time, the ratio of rf superimposed on dc is preferably 50 to 100% in terms of applied power and rf / dc. Further, rf is preferably a high frequency of 13.56 MHz ± 0.05%.
[0029]
In addition, three types of indium oxide, tin oxide, and gallium oxide, or two-way mixed sputtering of the above three types and the remaining two types of oxides are used to produce by multi-source simultaneous sputtering. A film may be formed. Furthermore, some or all of the individual sputtering targets may be replaced with metals or alloys.
[0030]
During film formation, sputtering is performed by introducing argon and oxygen as sputtering gases into a vacuum apparatus. In order to achieve a low resistivity of the film, the flow rate of the introduced gas is controlled and appropriately set to a value at which the resistivity decreases.
[0031]
The thin film thus obtained has a resistivity of 250 μΩ · cm or less, preferably 220 μΩ · cm or less, and Z-max / t of 10% or less, preferably 6% or less, and is extremely flat. With low resistivity. The thickness of the film to be formed is preferably 100 to 500 nm.
[0032]
In addition, the thin film formed on the substrate can be etched into a desired pattern as necessary, and then the device according to the third aspect of the present invention can be configured.
[0033]
It is also effective to add a fourth element for the purpose of imparting an additional function to the thin film according to the present invention. Examples of the fourth element include Mg, Al, Si, Ti, Zn, Y, Zr, Nb, Hf, and Ta. The addition amount of these elements is not particularly limited, but in order not to deteriorate the excellent electrical characteristics and flatness of the thin film according to the present invention, (total of oxides of fourth element) / (In ₂ O ₃ + SnO ₂ + Ga ₂ O ₃ + the sum of the oxides of the fourth element) / 100, and preferably over 0% and 20% or less (weight ratio).
[0034]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.
[0035]
Example 1
440 g of indium oxide powder, 60 g of tin oxide powder and a predetermined amount of gallium oxide powder were put in a polyethylene pot and mixed for 72 hours by a dry ball mill to produce a mixed powder.
[0036]
This powder was put into a mold and pressed at a pressure of 300 kg / cm ² to obtain a molded body. This compact was subjected to densification treatment with CIP at a pressure of 3 ton / cm 2. Next, this compact was placed in a pure oxygen atmosphere sintering furnace and sintered under the following conditions.
[0037]
(Sintering conditions)
Sintering temperature: 1500 ° C., heating rate: 25 ° C./hour, sintering time: 6 hours, oxygen pressure: 50 mmH ₂ O (gauge pressure), oxygen linear velocity: 2.7 cm / min When the density was measured by the Archimedes method, all were 95% or more. This sintered body was processed into a sintered body having a diameter of 4 inches and a thickness of 6 mm by a wet processing method, and was bonded to a backing plate made of oxygen-free copper using indium solder to obtain a target.
[0038]
The target was sputtered under the following sputtering conditions to evaluate the thin film.
[0039]
(Sputtering conditions)
Substrate: glass substrate, applied power: dc150W + rf100W, gas pressure: 1.1 mTorr, sputtering gas: Ar + O ₂ , O ₂ / Ar: controlled to values at which resistivity is minimized, substrate temperature: 200 ° C., film thickness: 200 nm.
[0040]
The composition of the obtained film was analyzed by EPMA (Electron Probe Micro Analysis), and the resistivity and Z-max / t of the thin film were measured. The obtained results are shown in FIG. Good results were obtained with a Ge / (In + Sn + Ge) content of 2-9%.
[0041]
Example 2
450 g of indium oxide powder, 50 g of tin oxide powder and a predetermined amount of gallium oxide powder were put in a polyethylene pot and mixed for 72 hours by a dry ball mill to produce a mixed powder.
[0042]
Using this powder, a target was produced in the same manner as in Example 1. A thin film was produced under the same conditions as in Example 1 using the obtained target.
[0043]
The composition of the obtained film was analyzed by EPMA, and the resistivity and Z-max / t of the thin film were measured. The obtained results are shown in FIG. Good results were obtained with a Ga / (In + Sn + Ga) content of 2-9%.
[0044]
Example 3
Of the targets manufactured in Example 1, sputtering was performed under the same conditions as in Example 1 except for the sputtering time, using a target whose Ga composition of the thin film was 4 atomic%, and a thin film having a thickness of 500 nm was formed. . When the resistance chamber and Z-max / t of the obtained film were measured, the resistivity was 198 μΩ · cm, and Z-max / t = 7.8%.
[0045]
Comparative Example 1
Of the targets manufactured in Example 1, the thin film was evaluated by sputtering under the following sputtering conditions using the target having a Ga composition of 4 atomic%.
[0046]
(Sputtering conditions)
Substrate: glass substrate, applied power: dc 200 W, gas pressure: 1.1 mTorr, sputtering gas: Ar + O ₂ , O ₂ / Ar: controlled to values with minimum resistivity, substrate temperature: 200 ° C., film thickness: 200 nm.
[0047]
When the resistance chamber and Z-max / t of the obtained film were measured, the resistivity was 280 μΩ · cm and Z-max / t = 28%.
[0048]
Comparative Example 2
Of the targets manufactured in Example 2, the thin film was evaluated by sputtering under the following sputtering conditions using the target having a Ga composition of 5 atomic%.
[0049]
(Sputtering conditions)
Substrate: glass substrate, applied power: dc 200 W, gas pressure: 1.1 mTorr, sputtering gas: Ar + O ₂ , O ₂ / Ar: controlled to values with minimum resistivity, substrate temperature: 200 ° C., film thickness: 200 nm.
[0050]
When the resistance chamber and Z-max / t of the obtained film were measured, the resistivity was 270 μΩ · cm and Z-max / t was 35%.
[0051]
【The invention's effect】
According to the present invention, it is possible to obtain a transparent conductive film having a flat film surface and low resistivity, which is suitable for a large high-definition EL panel.
[Brief description of the drawings]
FIG. 1 is a diagram showing a structure of an inorganic EL panel.
2 is a graph showing the resistivity and Z-max / t of the film obtained in Example 1. FIG.
3 is a graph showing the resistivity and Z-max / t of the film obtained in Example 2. FIG.

Claims (3)

It consists of indium, tin, gallium and oxygen, excluding inevitable impurities , gallium is contained in a ratio of 2% to 9% by atomic ratio of Ga / (In + Sn + Ga), and tin is 10% by atomic ratio of Sn / (Sn + In) A transparent conductive film characterized by being contained at a ratio of ˜14%, having a resistivity of 250 μΩ · cm or less and a maximum surface roughness (Z-max) / film thickness (t) of 10% or less. A device comprising the transparent conductive film according to claim 1. It consists of indium, tin, gallium and oxygen, excluding inevitable impurities , gallium is contained in a ratio of 2% to 9% by atomic ratio of Ga / (In + Sn + Ga), and tin is 10% by atomic ratio of Sn / (Sn + In) Sputtering target contained at a ratio of ˜14% is sputtered by sputtering power with rf superimposed on dc, and has a resistivity of 250 μΩ · cm or less and the maximum height difference of surface irregularities (Z-Max) / The manufacturing method of the transparent conductive film which film thickness (t) satisfies 10% or less.

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