JP2011202276A - Transparent electrode film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent electrode film having excellent etching characteristics while maintaining a favorable transmittance for visible light and a certain degree of electric resistance, and to provide a target to be used in a sputtering process for forming the above transparent electrode film, the target capable of reducing formation of nodules or abnormal discharge and having such a composition that contamination from a pulverization medium (zirconia) can be ignored in a pulverization process for supplying a powder with high sintering property in the production of the target.SOLUTION: The transparent electrode comprises indium oxide, and the indium oxide contains over 5 to 10 wt.% of zirconium oxide.

Description

  The present invention relates to a transparent electrode film used for a touch panel or the like and a sputtering target for forming the electrode film.

An ITO (indium-tin-based composite oxide: In ₂ O ₃ —SnO ₂ ) film is widely used as a transparent electrode (film) for a display device or the like centering on a liquid crystal display.
As a method of forming this ITO film, it is performed by means generally called physical vapor deposition such as vacuum vapor deposition or sputtering, and it is formed by magnetron sputtering particularly from the viewpoint of operability and film stability. ing.
A film is formed by sputtering, in which positive ions such as Ar ions are physically collided with a target placed on the cathode, and the material constituting the target is released by the collision energy, and the substrate on the anode side facing the target is released. This is done by stacking films having the same composition as the target material.
The coating method by sputtering has a feature that a thin film in angstrom units to a thick film of several tens of μm can be formed at a stable film formation speed by adjusting the processing time, supply power, and the like.

By the way, the ITO-based transparent electrode film that is most frequently used at present is excellent in visible light transmittance and conductivity, but mainly has the following problems.
One of them is that the film quality is not uniform and the etching characteristics at the time of circuit formation are poor. In recent years, display devices and display input devices have been demanded to increase the pixel density to provide a dense screen, and in accordance with this, it is required to make the transparent electrode pattern dense. For example, in a liquid crystal display device, there is a portion formed in a thin line having a wiring width of 20 to 50 μm, and high etching processability is required.
An IXO (In ₂ O ₃ —ZnO) film has been proposed as an improvement of the defects of the ITO transparent electrode film. However, this has significantly higher etching properties than the ITO film, but is inferior in conductivity, and has a problem of insufficient chemical resistance or water resistance against acids, alkalis and the like. Further, the improved etching property tends to be a disaster and tends to be over-etched, which is not necessarily an appropriate material.

The second problem is that a tin-rich phase exists in the ITO transparent electrode film forming target. This tin-rich phase causes nodules to be described later. That is, when the ITO film is formed by sputtering, fine protrusions called nodules are generated in the erosion portion of the target surface, thereby causing abnormal discharge and splash, thereby reducing the sputtering rate.
Further, the abnormal discharge and splash resulting from the nodules cause coarse particles to float in the sputtering chamber, which adheres to the film formed and causes the quality to deteriorate.
From the above, in actual production, it is necessary to periodically remove the nodules generated in the target, which has a problem that the productivity is remarkably reduced, and a target with little generation of nodules is demanded.

As the third problem, as a nodule reduction method, it is proposed to reduce the number of pores in the sintered body in order to increase the density of the sintered body as much as possible. It was required to make it finer.
In general, fine pulverization is performed using a container having zirconia beads and zirconia inner walls. However, there is a problem that contamination (contamination) from such pulverization media, that is, zirconia is mixed into the target material.
On the other hand, there is a problem that sintering in a pressurized state is necessary, and the equipment needs to be made larger in order to further increase the density, and it can be said that it is an industrially efficient method. There wasn't.

  As a publicly known document, the following Patent Document 1 (Japanese Patent Laid-Open No. 2-309511) can be cited. This cited document 1 describes a transparent electrode film in which 0 to 20 mol% of zirconium oxide is added to indium oxide. However, there is no description of density. It can be said that the invention is not interested in density at all and does not sufficiently grasp problems caused by density. Moreover, the transmittance | permeability of patent document 1 is about 90 to 91%, and is a very low transmittance. Technically the level is low and not helpful.

In an example of paragraph [0035] of the following Patent Document 2 (Japanese Patent Laid-Open No. 6-160876), it is described that sputtering is performed using a high-density target using indium oxide and zirconium oxide. However, there is no description in Patent Document 2 regarding how much density the high-density target has and how it is manufactured. Further, Patent Document 2 has no description of transmittance and is not helpful.

73 Examples are described in Tables 1 to 4 of Patent Document 3 (Japanese Patent Laid-Open No. 9-152940). Among them, sintered bodies of indium oxide and zirconium oxide are described in Example 7, Example 39, and Example 69. However, also in this patent document 3, there is no description about the density of the target, and there is no description about how to manufacture the target. Moreover, the transmittance | permeability obtained by sputtering the sintered compact of the indium oxide and a zirconium oxide described in the Example of patent document 3 is 89.1%, 85.1%, and 88.8%, and is remarkably low. The level of this Patent Document 3 is low and is not helpful.

A target using indium oxide and zirconium oxide is described in Example 5 of cited reference 4 of the following Patent Document 4 (Japanese Patent Laid-Open No. 9-209134), and the relative density of this target is described as 95%. Yes.
This is not a technique that can achieve a relative density of 97% or more, which is the target of the present invention. Further, this Patent Document 4 does not describe the transmittance at all, and cannot be said to be a level of technology that can be referred to.

The following Patent Document 5 (Japanese Patent Laid-Open No. 10-147862) is an ITO sintered body target made of indium oxide and tin oxide, and is a sintered body target made of indium oxide and zirconium oxide targeted by the present invention. The component composition is completely different.
Such materials with different component compositions are different in manufacturing process, and the structure and characteristics of the produced target and film are greatly different. Moreover, in this patent document 5, since there is no description which can implement | achieve the composition, relative density, and transmittance which this invention intends, it cannot be referred.

The following Patent Document 6 (Japanese Patent Laid-Open No. 11-157924) is an ITO sintered body target made of indium oxide and tin oxide, similar to the above-mentioned Patent Document 5, and is an indium oxide and zirconium oxide targeted by the present invention. The component composition is completely different from that of the sintered compact target.
Such materials with different component compositions have different manufacturing processes, and the structure and characteristics of the prepared target and film are greatly different. In Patent Document 6, there is no description that can realize the composition, relative density, and transmittance intended by the present invention, and therefore it cannot be referred to.

The following Patent Document 7 (Japanese Patent Laid-Open No. 11-157924) and Patent Document 8 (Japanese Patent Laid-Open No. 2001-81551) are similar to Patent Documents 5 and 6, and an ITO sintered body target composed of indium oxide and tin oxide. However, the component composition is completely different from the sintered body target made of indium oxide and zirconium oxide, which is the target of the present invention.
Such materials with different component compositions have different manufacturing processes, and the structure and characteristics of the prepared target and film are greatly different. In Patent Documents 7 and 8, since there is no description that can realize the composition and transmittance intended by the present invention, it cannot be referred to.

JP-A-2-309511 JP-A-6-160876 JP-A-9-152940 JP-A-9-209134 JP-A-10-147862 JP-A-11-157924 JP 2001-151572 A JP 2001-81551 A

An object of the present invention is to provide a transparent electrode film excellent in etching characteristics while solving the above-mentioned problems, maintaining good visible light transmittance and a certain electric resistance.
Also provided is a target capable of reducing the formation of nodules and abnormal discharge in the sputtering process for forming this transparent electrode film.
Furthermore, a target having a composition in which contamination (contamination) from pulverization media (zirconia) can be ignored in a pulverization process for supplying a powder having high sinterability during production of the target.

The present invention
1. 1. Transparent electrode film comprising 5% by weight (extra) to 10% by weight of zirconium oxide in indium oxide. Provided is a sputtering target for forming a transparent electrode film characterized by containing 5 wt% (over) to 10 wt% of zirconium oxide in indium oxide.
3. 3. The sputtering target for forming the transparent electrode film according to 2 above, wherein the diameter of the zirconium phase by EPMA observation is 5 μm or less.

  While maintaining a good visible light transmittance and a relatively high specific resistance to a certain degree, a transparent electrode film having an appropriate etching property is obtained, and in a sputtering process for forming the transparent electrode film, a high density is obtained. Efficiently produce a sintered compact target with little nodule generation, thereby suppressing the decline in productivity and quality caused by nodule generation, and obtaining a target that can ignore contamination (contamination) from the grinding media It has the excellent feature of being able to. Moreover, it is excellent in the film | membrane characteristic at room temperature or low temperature, and it is effective when using as a board | substrate the plastic sheet and film inferior to heat resistance instead of a glass substrate from weight reduction, such as a liquid crystal display.

It is a figure which shows the precipitate of the zirconium phase by EPMA observation.

The conductivity of the transparent conductive film is generally represented by a sheet resistance (Ω / □), and usually a sheet resistance of about 5Ω / □ is required. When applied to the liquid crystal display screen as described above, With higher definition, lower sheet resistance is required.
The area resistance is represented by a value obtained by dividing the specific resistance by the thickness of the transparent conductive film. Therefore, the area conductivity of the transparent conductive film is expressed by the product of the conductivity (reciprocal of the specific resistance) and the film thickness, and this conductivity σ (Ω ⁻¹ · cm ⁻¹ ) is the carrier (hole) contained in the film. Or (electrons) charge e (coulomb), carrier mobility μ (cm ² / V · sec) and carrier concentration n (cm ⁻³ ) (σ (Ω ⁻¹ · cm ⁻¹ ) = e · μ · n).
Therefore, in order to improve the conductivity of the transparent conductive film and reduce the specific resistance (also referred to as resistivity) and the sheet resistance, the carrier mobility μ (cm ² / V · sec) and the carrier concentration n (cm ⁻ Any one or both of ³ ) may be increased.

From this, as a dopant for increasing the carrier concentration n, attention was focused on zirconium oxide (ZrO ₂ ), which is solid-solved in indium oxide (In ₂ O ₃ ) at a high concentration (up to 5% by weight). As will be described later, it has been found that this zirconium oxide dopant can maintain good visible light transmittance and high conductivity. The present inventors have already filed this as Japanese Patent Application No. 2001-025078.
On the other hand, it can be understood from this that the specific resistance of the obtained film increases as the content of zirconium oxide (ZrO ₂ ) exceeds 5% by weight. Therefore, it was found that the adjustment of the zirconium concentration is effective for obtaining a film having a certain high specific resistance. That is, such a film having a relatively high specific resistance is more effective as a raw material for a touch panel.
Further, this zirconium oxide dopant is not as high as SnO ₂ which is a component of ITO with respect to acid resistance, but is not as low as ZnO and has an excellent feature that appropriate etching characteristics can be obtained.

Furthermore, in the present invention, the diameter of the zirconium phase in the target can be 5 μm or less. In the target, it exists as a composite solution of indium oxide and zirconium oxide or as a solid solution in indium oxide. However, zirconium oxide is solid-solved until the concentration of zirconium oxide is close to 5%, and it increases as the amount increases. Instead, a zirconium phase is precipitated by EPMA observation.
This zirconium phase is a heterogeneous phase in the target, and if it becomes large, it may cause nodules and arcing in long-time sputtering, and in the extreme case, the composition of the sputtered film may become non-uniform. Therefore, generation of nodules and arcing can be prevented by setting such a zirconium-containing precipitated phase to 5 μm or less and uniformly dispersing it.

Furthermore, as a factor which influences the film characteristics at the time of sputtering, the density of the target can be mentioned as described above, and the higher the target density, the more stable sputtering characteristics and a good film can be obtained.
In order to improve the density of the target, it is known that the finer the powder before molding, the better. Zirconium oxide (zirconia) can be used as a dopant to be added to indium oxide, and at the same time, zirconium oxide can be used as a medium for fine pulverization, that is, can be pulverized using a container of zirconia beads or zirconia lining, There is a great advantage that the grinding media itself does not become a contamination source.
As a result, the level of pulverization can be improved, and a sputtering target having a much higher purity and a higher density than conventional can be obtained.
Moreover, by using such a high-density target, the generation of nodules is suppressed, the generation of particles caused by abnormal discharge and splash due to the nodules is suppressed, and the quality of the conductive film is effectively reduced. It has the feature that it can be suppressed.

  Next, examples of the present invention will be described. In addition, a present Example is an example to the last, and is not restrict | limited to this example. That is, all aspects or modifications other than the embodiments are included within the scope of the technical idea of the present invention.

(Examples 1-3)
Indium oxide (In ₂ O ₃ ) powder and zirconium oxide (ZrO ₂ ) powder were weighed to 6, 7, and 8% by weight, and then zirconia (ZrO ₂ ) balls (beads) were used as grinding media. Mixing and fine grinding were performed to obtain a mixed powder slurry having a median diameter of 0.8 μm. In addition, it is set as Example 1, 2, and 3 about the case where the said zirconium oxide powder is 6, 7, and 8 weight%, respectively.
This slurry was granulated to obtain a spherical granulated powder. Furthermore, this granulated powder was press-molded, and further CIP (isotropic cold pressing) was performed. The molded body was sintered in an oxygen atmosphere at a temperature of 1640 ° C. for 4 hours to obtain a sintered body (hereinafter referred to as “IZO sintered body”). The sintered density reached 99% or more. This sintered body was ground and cut, and processed into a sputtering target having a predetermined shape.

Next, a transparent electrode film was formed on the glass substrate by DC sputtering using the IZO sintered compact target under the following conditions.
Sputtering gas: Ar + O ₂
Sputtering gas pressure: 0.5Pa
Electricity amount: 60W
Deposition rate: about 300cm / min
The nodule generation amount (coverage) in this case was measured, and the nodule coverage in the IZO sintered body of this example was 10% or less.

Further, the film characteristics of the specific resistance (Ω · cm) of film formation and the transmittance% at 550 nm were examined, and the results are shown in Table 1. Table 1 shows film characteristics at the time of film formation at room temperature and an oxygen concentration of 1%.
For comparison, Table 1 shows the specific resistance (Ω · cm) of the ITO film (Comparative Example 1) and the IXO film (Comparative Example 2) produced under the same conditions and the film characteristics of transmittance% at 550 nm. Posted.
As is apparent from Table 1, the specific resistance is high and the transmittance is almost the same as that of the ITO of the example of the present invention and that of the comparative example 1, and the good visible light transmittance of the example of the present invention is high. It can be seen that the resistivity is shown. In addition, there was a certain correlation between the increased amount of zirconium oxide and the specific resistance of the film obtained by sputtering, and the specific resistance of the film tended to increase with increasing zirconium oxide.
In general, the IZO film using the IZO sintered compact target of the present invention with respect to the ITO film does not have much difference in the film characteristics when the substrate temperature is increased, but the characteristics of the film formed at room temperature are similar. The result was better.

Table 2 shows the measurement results of the zirconium oxide concentration and density in the targets of Examples 1 to 3 and Comparative Examples 1 and 2. As shown in Table 2, the relative densities of Examples 1 to 3 all exceed 97%, and the relative density is improved as the zirconium oxide concentration is increased. Although not shown in this table, the relative density reached 98.7% at a zirconium oxide concentration of 10 wt%. This makes it possible to form a sputtered film that is uniform and excellent in quality.
On the other hand, the densities of the targets of Comparative Examples 1 and 2 were 93% and 87%, respectively, which were lower and worse than this example. The nodule coverage reached 70%.
Furthermore, when the concentration of zirconium oxide was increased, it was observed that the zirconium phase (zirconium oxide phase) was precipitated without being completely dissolved. FIG. 1 is an EPMA observation result (1000 times) of a target having a zirconium oxide content of 6 wt% (Example 1). In FIG. 1, fine precipitates having a zirconium phase diameter of less than 1 μm are observed. Such a precipitate does not generate nodules or arcing during sputtering, and there is no possibility that the composition of the sputtered film becomes non-uniform.

In recent years, plastic sheets and films tend to be used in place of glass substrates due to weight reduction and cost reduction of equipment. Since plastics are inferior in heat resistance, there is a demand for film formation at a low temperature without heating the substrate. Therefore, the transparent electrode of the present invention having excellent film properties at room temperature or low temperature as described above meets this purpose and can be said to be an excellent material.
Further, in Comparative Examples 1 and 2, it was confirmed that the zirconia contamination was remarkably increased when pulverization to 0.8 μm or less, which was the same as in this example, was performed.

Next, the relationship between the substrate temperature and the etching rate is shown in Table 3 for the transparent electrode films of the above Examples and Comparative Examples 1 and 2. The etchant used was a mixed acid of HCl: H ₂ O: HNO ₃ = 1: 1: 0.08.
As is apparent from Table 3, it can be seen that the etching rate of IZO, which is the present example, is higher when the substrate temperature is room temperature and when the substrate temperature is 200 ° C. than the comparative example 1 that is ITO. The difference is particularly remarkable when the substrate temperature is 200 ° C.
Further, the IXO of Comparative Example 2 has an abnormally high etching property at room temperature of 92700 Å / min and 90900 Å / min at 200 ° C, but is not preferable because it tends to cause over-etching.

  While maintaining a good visible light transmittance and a relatively high specific resistance to a certain degree, a transparent electrode film having an appropriate etching property is obtained, and in a sputtering process for forming the transparent electrode film, a high density is obtained. Efficiently produce a sintered compact target with little nodule generation, thereby suppressing the decline in productivity and quality caused by nodule generation, and obtaining a target that can ignore contamination (contamination) from the grinding media It has the excellent feature of being able to. Further, it is excellent in film properties at room temperature or low temperature, and is particularly useful when a plastic sheet or film having inferior heat resistance is used instead of a glass substrate due to weight reduction of a liquid crystal display or the like.

Claims (3)

A transparent electrode film comprising 5% by weight (over) to 10% by weight of zirconium oxide in indium oxide. A sputtering target for forming a transparent electrode film, comprising 5% by weight (over) to 10% by weight of zirconium oxide in indium oxide. The sputtering target for forming a transparent electrode film according to claim 2, wherein the diameter of the zirconium phase by EPMA observation is 5 μm or less.