JP5761670B2 - Sputtering target for forming transparent conductive film and method for producing the same - Google Patents

Description

The present invention relates to a sputtering target for forming a transparent electrode film used for a display device or the like centering on a liquid crystal display.

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 an inner wall of zirconia. 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 publicly known documents, the following patent documents can be cited, but as a means for obtaining a transparent electrode film having appropriate etching properties while maintaining good visible light transmittance and high conductivity, it is sufficient. Has no function.

JP-A-2-309511 JP-A-9-152940 JP-A-10-158827 JP 2000-226254 A

The present invention provides a transparent electrode film having an appropriate etching property while solving the above-mentioned problems, maintaining good visible light transmittance and high conductivity.
In addition, in the sputtering process for forming this transparent electrode film, a sintered body target with a high density and less nodule generation is efficiently produced, thereby suppressing a decrease in productivity and quality due to the generation of nodules, Furthermore, it aims at obtaining the target which can ignore the contamination (contamination) from the grinding media.

The present invention
1 Transparent electrode film comprising zirconium oxide in an indium oxide content of 0.1 to 5% by weight and zirconium oxide in the indium oxide 2 0.1 to 5 zirconium oxide in the indium oxide There is provided a sputtering target for forming a transparent electrode film, which is contained by weight and zirconium oxide is dissolved in the indium oxide.

  A transparent electrode film having an appropriate etching property while maintaining good visible light transmittance and high conductivity is obtained, and in the sputtering process for forming the transparent electrode film, high density and little nodule generation are obtained. An excellent production of a sintered compact target that effectively suppresses the decline in productivity and quality caused by the generation of nodules, and can obtain a target that can ignore contamination (contamination) from the grinding media. It has the features. In addition, the film characteristics at room temperature or low temperature are excellent.

It is an XRD measurement result with a zirconium oxide content of 10% by weight. It is an XRD measurement result with a zirconium oxide content of 5% by weight. It is an XRD measurement result with a zirconium oxide content of 1% by weight.

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 and the sheet resistance, one of the carrier mobility μ (cm ² / V · sec ₂ and the carrier concentration n (cm ⁻³ )) Or both may be increased.

From this, the present inventors focused on zirconium oxide (ZrO ₂ ), which is a solid solution at a high concentration (up to 5 wt%) in indium oxide (In ₂ O ₃ ) as a dopant for increasing the carrier concentration n. .
As will be described later, it has been found that this zirconium oxide dopant can maintain good visible light transmittance and high conductivity.

If the content of zirconium oxide (ZrO ₂ ) exceeds 5% by weight, zirconium oxide cannot be dissolved in indium oxide, and excess zirconium oxide particles are precipitated, thereby deteriorating the transmittance. On the other hand, if it is less than 0.1% by weight, the function as a zirconium oxide dopant cannot be produced, and good visible light transmittance and high conductivity cannot be maintained. Therefore, it is necessary to contain 0.1 to 5% by weight of zirconium oxide in indium oxide.

This zirconium oxide dopant has an excellent feature that the acid resistance is not as high as SnO ₂ which is a component of ITO but is not as low as ZnO, and appropriate etching characteristics can be obtained.
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, the finer the powder before molding, the better. However, the above-mentioned zirconium oxide (zirconia) dopant uses an existing grinding media, that is, a container of zirconia beads or zirconia lining for grinding. There is a great advantage that the pulverization medium itself does not become a contamination source (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. 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.

(Example)
After a predetermined amount of zirconium oxide (ZrO ₂ ) powder is mixed with indium oxide (In ₂ O ₃ ) powder so as to be 5% by weight, fine pulverization is performed using zirconia (ZrO ₂ ) balls (beads) as grinding media. It was. In order to increase the sintered density, pulverization was performed to 0.8 μm or less.
Using this mixed powder, press molding was performed at a pressure of 1 t (tons) / cm ² to obtain a molded body of φ200 × 8 (mm), and further CIP (isotropic cold pressing) was performed. Then, this compact was sintered in an oxygen atmosphere at a temperature of 1640 ° C. for 4 hours to obtain a sintered compact (hereinafter referred to as “IZO sintered compact”) target. The sintered density reached 98%.

The solid solution of zirconium oxide was confirmed by XRD (X-ray diffraction) of the IZO sintered compact target. For comparison, IZO with a zirconium oxide content of 1% by weight and a zirconium oxide content of 10% by weight (outside the scope of the present invention) under the same conditions as in the above example, except for the zirconium oxide content of 5% by weight of the example. A sintered compact target was created.
FIG. 1 shows the results of XRD measurement with a zirconium oxide content of 10% by weight. Moreover, the XRD measurement result in an IZO sintered compact target with a zirconium oxide content of 5% by weight and a zirconium oxide content of 1% by weight is shown in FIGS.

In the target containing 10% by weight of zirconium oxide in FIG. 1, the peak of cubic ZrO ₂ is observed at 2θ of 30.24 degrees, 35.04 degrees, 50.36 degrees, and 60.24 degrees. It can be seen that ZrO ₂ is not completely dissolved.
Note that these peaks are close to the peaks of cubic In ₂ O ₃ at 30.50 degrees, 35.38 degrees, 50.94 degrees, and 60.56 degrees, so at first glance, the peaks of In ₂ O ₃ are on the lower angle side. It seems to have spread.
However, as shown in FIGS. 2 and 3, these peaks are not observed in the IZO sintered target in the range of the present invention in amounts containing zirconium oxide 5% by weight and zirconium oxide content of 1 wt%, ZrO ₂ is You can see that it is in solid solution.

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: 0.4 Pa
Sputtering gas flow rate: 8SCCM
Oxygen concentration: 1%
Input power: 0.5 W / cm ²
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 and the transmittance are almost the same as those of the example of the present invention and the ITO of the comparative example 1, and the good visible light transmittance and high conductivity of the example of the present invention are obtained. You can see that it is maintained.
In general, the IZO film using the IZO sintered compact target of the present invention is not much different from the ITO film when the substrate temperature is raised, but the characteristics of the film formed at room temperature are much different. The result was excellent.

  In recent years, there is a tendency to use a plastic sheet or a film instead of a glass substrate because of weight reduction of a liquid crystal display or the like. 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.

On the other hand, in the IXO film of Comparative Example 2, the transmittance is high, but the specific resistance is extremely low. 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.
In addition, the densities of the targets of Comparative Examples 1 and 2 were 93% and 87%, respectively, which were lower than that of the present example, and the nodule coverage reached 70%.

Next, the relationship between the substrate temperature and the etching rate is shown in Table 2 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 2, it can be seen that the etching rate of IZO, which is the present example, is superior when the substrate temperature is room temperature and when the substrate temperature is 200 ° C., as compared with 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.

  A transparent electrode film having an appropriate etching property while maintaining good visible light transmittance and high conductivity is obtained, and in the sputtering process for forming the transparent electrode film, high density and little nodule generation are obtained. An excellent production of a sintered compact target that effectively suppresses the decline in productivity and quality caused by the generation of nodules, and can obtain a target that can ignore contamination (contamination) from the grinding media. It has the features. 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 (2)

Containing zirconium oxide 0.1-5 wt% in indium oxide, zirconium oxide and a solid solution total volume of oxide in the indium, a transparent electrode film sintered density of the sintered target is reach 98% Sputtering target to do.   After mixing 0.1 to 5% by weight of zirconium oxide powder with indium oxide powder, the mixture powder is pulverized to 0.8 μm or less using zirconia balls as a pulverization medium, and this mixed powder is press-molded to form a molded body. Isotropic cold pressing), sintered at 1640 ° C. in an oxygen atmosphere, the sintered target reaches a sintering density of 98%, and the sintered compact target in which the entire amount of zirconium oxide is dissolved in the indium oxide; A method for producing a sputtering target for forming a transparent electrode film, characterized in that:

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