JP4213611B2 - ITO sputtering target - Google Patents

Description

  The present invention relates to an ITO sputtering target for forming a transparent conductive film in which nodule generation is small during film formation by sputtering, and abnormal discharge and particles are unlikely to occur.

An ITO thin film for forming a transparent conductive film is widely used as a transparent electrode of a display device centering on a liquid crystal display. In many cases, the ITO thin film is formed by sputtering, but when sputtering is performed using an ITO target, a crushed black protrusion having a size of several μm to several mm is formed on the erosion portion of the target surface. Many appear.
This protrusion is considered to be a lower oxide of indium and is generally called a nodule.

  The nodules increase as the number of sputtering increases and gradually increase over the target surface. Nodules have poor electrical conductivity compared to other parts, and if the amount of nodules generated is large, abnormal discharge (arcing) occurs frequently during sputtering, resulting in particles in the ITO film, and thus it is difficult to continue sputtering. There was a problem of becoming.

  The generation of nodules is a problem peculiar to the ITO target for forming a transparent conductive film. When the nodules increase abnormally on the target surface, the sputtering operation is temporarily stopped and the nodules generated on the target surface are scraped off. However, such interruption of sputtering is a factor that significantly reduces productivity in continuous operation. And although this reproduction | regeneration work itself is simple, it requires a certain skill and time, and cannot avoid complexity.

In addition, there is a limit to the regeneration process of scraping off the above-mentioned nodules, and it is actually difficult to reproduce to the same extent as a newly created IT0 sputtering target. As a result, before the target is used up (the life of the target that is consumed in a normal state), the target is often unusable due to an increase in the amount of nodules generated. For this reason, there is a demand for an ITO sputtering target in which the amount of nodules generated is low in terms of both productivity and material cost.

  An ITO sputtering target is generally obtained by grinding a sintered body with a lathe or the like, but it is speculated that the ITO grinding powder adhering to the target surface is one of the causes of nodule generation. Therefore, it is expected that the amount of nodule generation can be reduced by reducing the amount of this ITO grinding powder, but knowing the limit value of the amount of ITO grinding powder until the nodule reduction effect starts to appear, In addition, it was difficult to reduce the amount of ITO grinding powder to the limit value at the actual operation scale.

Therefore, in order to reduce the amount of grinding powder adhering to the target surface by trial and error, a technique of polishing using a wet rotary polishing machine has been proposed (see Patent Document 1), or grinding dust is removed by sandblasting. A reduction was made. (See Patent Document 2).
However, although these methods can reduce the amount of grinding powder to a certain extent, they still have a large amount of ground ITO scraps, etc., which is not sufficient. Therefore, since the limit value of the amount of grinding powder is unknown in this way, there is no actual confirmation that the amount of grinding powder adhering to the target surface is one of the causes of nodule generation. It seems to be correct.
JP-A-8-60352 JP-A-9-104973

  The present invention further provides an ITO sputtering target for forming a transparent conductive film, in which the surface of the target is further cleaned, less nodules are generated during film formation by sputtering, and abnormal discharge and particles are less likely to occur.

The present invention
1. The number of adhering particles having an average diameter of 0.2 μm or more present in an area of 100 μm × 100 μm on the surface to be sputtered obtained by multi-frequency ultrasonic cleaning of the sputtering surface of the ITO sputtering target sintered body is 400 or less. Yes, the following sputtering conditions (sputtering gas: Ar + O ₂ , sputtering gas pressure: 0.5 Pa, sputtering gas flow rate: 300 sccm, oxygen concentration in sputtering gas: 1%, leakage magnetic flux density: 400 Gauss, input sputtering power density: 1 W / ITO sputtering target capable of achieving 0.1% nodule coverage (nodule area / erosion part area) when sputtered with cm ² , sputtering time: continuous 20 hours . The number of adhered particles to provide an ITO sputtering target according to claim 1, characterized in that it is 100 or less.

  Remove most of the ground from ITO particles, such as ground ITO scraps that are adhering in large quantities to the surface of the ITO sputtering target for transparent conductive film formation, and further improve the cleaning of the target surface. There is little generation of nodules during film formation by sputtering, and there is an excellent effect that abnormal discharge and particles are hardly generated.

In the production of an ITO sputtering target, for example, an indium oxide powder having an average particle size of μm and a tin oxide powder having the same particle diameter are weighed so as to have a weight ratio of 90:10, and a molding binder is added to this to uniformly Mix. Next, the mixed powder is filled in a mold, press-molded, and then sintered at a high temperature.
The ITO sputtering target sintered body obtained in this way is ground with a surface grinder to obtain an ITO target material. As described above, a large amount of grinding ITO scraps are adhered. Such grinding ITO scraps cause direct and large generation of nodules. For this reason, in the finishing process, the surface of the ITO target is polished and smoothed, for example, using sandpaper until the traces of the surface grinding wheel running as much as possible remain.

Sand blasting is also effective in this finishing process. As the blasting material, glass beads, alumina beads, or zirconia beads are used, which is effective in reducing unevenness having edges on the surface of the ITO target and removing grinding debris between these unevennesses.
Next, a cleaning process such as air blow or running water cleaning is performed. When removing foreign matter by air blow, it can be removed more effectively if air is sucked into the dust collector from the opposite side of the nozzle. However, it has been found that there is a limit to the above air blow and running water cleaning, and fine debris still remains even when such a cleaning process is performed.

As a method for solving this, ultrasonic cleaning is performed. Although this ultrasonic cleaning is more effective than other cleaning treatments, it has been found that a simple ultrasonic cleaning operation cannot provide such an effect.
For this reason, as a result of repeatedly performing various tests, it was found that a method of performing ultrasonic cleaning by causing multiple oscillations between frequencies of 25 to 300 KHz was found to be particularly effective. Among these, ultrasonic cleaning by the following multiple oscillation is the most effective.
That is, when a 25 KHz single frequency or a 75 KHz single frequency is applied, the cleaning effect hardly appears. As shown in Examples described later, for example, an excellent cleaning effect was obtained when ultrasonic cleaning was performed by oscillating 12 types of frequencies at 25 KHz increments between 25 to 300 KHz.

  By the above operation, adhered particles having an average diameter of 0.2 μm or more (ITO grinding) existing in a 100 μm × 100 μm area (100 μm square surface) of the surface to be sputtered of the ITO sputtering target by the ultrasonic cleaning method using the multiple oscillation described above. The number of powders) was less than 400. Here, “average diameter” means that the adhering particles themselves are not circular but have irregular shapes, and therefore the average diameter of the passing dimensions of the particles is taken as the diameter of the diameter when replaced with a circle. To do.

In particular, in ultrasonic cleaning by multiple oscillation, this number can be further reduced. Adhesive particles having an average diameter of 0.2 μm or more existing in an area of 100 μm × 100 μm on the surface to be sputtered of the ITO sputtering target (ITO grinding powder) ) Could be 100 or less.
In the case of an ITO sputtering target product that has undergone a normal cleaning process, this man-hour is around 1000, so it can be said that a dramatic improvement has been made.

More importantly, the number of adhered particles (ITO grinding powder) having an average diameter of 0.2 μm or more existing in an area of 100 μm × 100 μm of the ITO sputtering target is 400 or less, preferably 100 or less. This means that the number of slabs could be significantly reduced.
As a result, it was possible to elucidate the cause of the generation of nodules, which had been only speculated until now, and to clarify the critical amount of adhered particles (ITO grinding powder).

And, as shown in the following examples, the amount of nodules generated in the ITO sputtering target is reduced, and the regeneration process such as scraping off the nodules generated on the target surface by temporarily stopping the sputtering operation is unnecessary or necessary. Even in such a case, the number of times can be reduced, and productivity can be remarkably increased.
Even in the case of removing ITO grinding powder by ultrasonic cleaning according to the present invention, surface treatment by sandpaper or sandblasting and cleaning treatment by air blow or running water cleaning or removal of ITO grinding powder by peeling off an adhesive tape may be appropriately performed.

Subsequently, the present invention will be described with reference to comparative examples by way of examples.
Example 1
In the production of the ITO sputtering target, first, the iridium oxide powder having an average particle size of 2 μm and the tin oxide powder having the same particle size were weighed so as to have a weight ratio of 90:10, and a molding binder was added thereto and mixed uniformly. . Next, this raw material mixed powder was uniformly filled into a mold (165 W × 520 L), and pressure-molded with a hydraulic press at a pressure of 800 Kgf / cm ² . The molded body thus obtained was sintered at 1640 ° C. for 7 hours in a pure oxygen gas atmosphere at 1 atm (absolute pressure) by a pressure sintering furnace.
Thus, the sputter | spatter surface of the sintered compact obtained was ground with the surface grinder, and also the side was cut | disconnected with the diamond cutter, and it was set as the ITO target material. The density of this ITO target material was 7.05 g / cm ³ .

Next, this ITO target material is bonded to a backing plate. In the surface finishing process after bonding, sandpaper is used and polished until the traces of the surface grinding wheel run are left smooth, or sandblasted using zirconia beads.
Next, the sputter surface was blown with air, and further, 12 types of frequencies were oscillated at 25 KHz intervals between frequencies of 25 to 300 KHz, and ultrasonic cleaning was performed for 3 minutes. The respective frequencies are 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, and 300 KHz. Thereafter, it was dried to obtain an ITO sputtering target as an example of the present invention.

(Comparative Examples 1-3)
The sputter surface of the sintered body obtained under the same conditions as in the example was ground with a surface grinder, and the sides were cut with a diamond cutter and bonded to a backing plate as an ITO target material. (Comparative example 1), ultrasonic cleaning by 75 KHz single frequency oscillation after the air blowing (comparative example 2), and ultrasonic cleaning by 25 KHz single frequency oscillation after the air blowing (comparative example 1) An ITO sputtering target as Comparative Example 3) was prepared.

(Comparison with the comparison test with Example 1 and Comparative Examples 1-3)
A sputtering test was performed on the ITO sputtering targets of Example 1 and Comparative Examples 1 to 3 prepared as described above under the following conditions.
Sputtering gas: Ar + O ₂
Sputtering gas pressure: 0.5Pa
Sputtering gas flow rate: 300 SCCM
Oxygen concentration in sputtering gas: 1%
Leakage magnetic flux density: 400 Gauss
Sputtering power density: 1 W / cm ²
Sputtering time : 20 hours continuous

The appearance of the target after sputtering under the above conditions is as shown in FIGS. In addition, as for the target of FIGS. 1-3, what smoothened using the sandpaper for surface finishing was used for all.
The target 1 shown in FIG. 1 is subjected to air-blowing which is Example 1 of the present invention, and then subjected to ultrasonic cleaning for 3 minutes by oscillating 12 types of frequencies in 25 KHz increments between 25 to 300 KHz for 3 minutes. It is the external appearance of the target which implemented the said sputtering.

Further, the target 1 shown in FIG. 2 and FIG. 3 is based on an example in which the sputtering is performed after air cleaning by 75 KHz single frequency oscillation after air blowing (Comparative Example 2) and by 25 KHz single frequency oscillation after the air blowing. It is the external appearance of the target of the example (comparative example 3) which performed the said sputtering after performing ultrasonic cleaning.
As is apparent from FIGS. 1, 2 and 3, the ultrasonic cleaning by the 75 KHz single frequency oscillation which is a comparative example is performed (comparative example) as compared with the ultrasonic cleaning by the multiple oscillation of the present invention. In 2) and in the case of Comparative Example 3) in which ultrasonic cleaning by single frequency oscillation of 25 KHz was performed, a black projection having a size of several μm to several mm was formed on the erosion portion 3 on the surface of the target 1 after the completion of sputtering. That is, it can be seen that many nodules appear. The fewer black spots, the better the target.

Table 1 shows a comparison of the nodule coverage after the sputtering test between Example 1 and Comparative Examples 1 to 3. Here, the “nodule coverage” is the ratio of “nodule area / erosion area” on the sputtering target surface expressed in%. As is apparent from Table 1, it can be seen that in the examples of the present invention, the coverage is significantly reduced as compared with the comparative examples.
In Table 1, for reference, an example in which only the air blowing was performed on the sputtering surface (Comparative Example 1) was given. As is clear from these, the target of Comparative Example 1 has the worst nodule coverage. In addition, the ultrasonic cleaning by the 75 KHz single frequency oscillation of Comparative Example 2 and the ultrasonic cleaning by the 25 KHz single frequency oscillation of Comparative Example 3 have a slightly improved effect than Comparative Example 1, but greatly improved. It can be seen that a significant effect cannot be expected.

Furthermore, FIG. 4 is an electron micrograph of the target surface that was smoothed with sandpaper for the surface finish of the ITO target material and then only air blow was performed ((a) is 500 times and (B) is 5000 times ( The same shall apply hereinafter)). This is the ITO target before performing the sputtering test of Comparative Example 1.
As is clear from FIGS. 4A and 4B, the ITO target surface before the sputtering test of Comparative Example 1 has countless sesame-like crushed debris on the wavy (wrinkled) surface or gaps. Exists.

FIGS. 5 (a) and 5 (b) show targets obtained by similarly smoothing the surface of the ITO target material using sandpaper, then air blowing, and further performing ultrasonic cleaning by 75 KHz single frequency oscillation. It is an electron micrograph of the surface. This is the ITO target before performing the sputtering test of Comparative Example 2.
As is clear from FIGS. 5A and 5B, the ITO target surface before performing the sputtering test of Comparative Example 2 has an infinite number of sesame crushing debris on the wavy surface or gap.

FIGS. 6A and 6B are similar targets obtained by smoothing the surface of the ITO target material using sandpaper, then air blowing, and further performing ultrasonic cleaning by 25 KHz single frequency oscillation. It is an electron micrograph of the surface. This is the ITO target before performing the sputtering test of Comparative Example 3.
As is clear from FIGS. 6A and 6B, the ITO target surface before performing the sputtering test of Comparative Example 3 has an infinite number of sesame-like crushed debris on the wavy surface or gap.

7 (a) and 7 (b), similarly, the surface of the ITO target material is smoothed by using sandpaper, and then air blow is performed. Further, the present invention has 12 types of 25 to 300 KHz in increments of 25 KHz. It is the electron micrograph of the target surface obtained by performing ultrasonic cleaning by multiple oscillation of frequency. This is the ITO target before performing the sputtering test of the example.
As is clear from FIGS. 7A and 7B, in Example 1 of the present invention, almost no sesame-like crushing is observed on the wavy surface or gap as described above, and the cleanliness of the surface is low. It can be easily understood that it is extremely high.

  One cause of nodule generation is the presence of dust on the target surface. Although a large amount of ground ITO scraps and the like are attached to the target surface, it has been found that they are very fine particles and cannot be removed by air blow or simple ultrasonic cleaning. Effective ITO grinding powder removal was achieved for the first time by ultrasonic cleaning by multiple oscillation of the present invention or by combining this with the finishing treatment and cleaning treatment described above.

One cause of nodule generation is the presence of dust on the target surface. Although a large amount of ground ITO scraps and the like are attached to the target surface, it has been found that they are very fine particles and cannot be removed by a conventional cleaning process such as air blow.
On the other hand, according to the actual measurement, the number of adhered particles having an average diameter of 0.2 μm or more existing in an area of 18 μm × 21.5 μm was 1 in the multi-oscillation ultrasonic cleaning product according to the example of the present invention.
Thus, by combining the multi-oscillation ultrasonic cleaning method of the present invention or the finishing treatment and the cleaning treatment described above, an extremely high cleaning effect that could not be removed by the conventional cleaning treatment was achieved for the first time.

  Remove most of the ground from ITO particles, such as ground ITO scraps that are adhering in large quantities to the surface of the ITO sputtering target for transparent conductive film formation, and further improve the cleaning of the target surface. There is little generation of nodules during film formation by sputtering, and it has an excellent effect that abnormal discharge and particles are hardly generated, and is useful as an ITO sputtering target.

It is an external view of the surface of a target after carrying out ultrasonic cleaning by carrying out multiple oscillation, and sputtering a target for 20 hours continuously after that. It is an external view of the target surface after performing sputtering for 20 hours continuously after performing ultrasonic cleaning by 75 KHz single frequency oscillation. It is an external view of the target surface after performing the ultrasonic cleaning by 25 KHz single frequency oscillation, and sputtering a target for 20 hours continuously. It is the electron micrograph of the target surface which smooth | blunted the surface of the ITO target material using sandpaper, and gave only air blow after that. It is an electron micrograph of the target surface obtained by carrying out air blow and performing ultrasonic cleaning by 75 KHz single frequency oscillation. It is an electron micrograph of the target surface obtained by carrying out air blow and performing ultrasonic cleaning by 25 KHz single frequency oscillation. It is an electron micrograph of the surface of a target obtained by carrying out air blow and performing ultrasonic cleaning by multiple oscillation between 25 to 300 KHz of the present invention.

Explanation of symbols

1 Target 2 Peripheral part 3 erosion part of target

Claims (2)

The number of adhering particles having an average diameter of 0.2 μm or more present in an area of 100 μm × 100 μm on the surface to be sputtered obtained by multi-frequency ultrasonic cleaning of the sputtering surface of the ITO sputtering target sintered body is 400 or less. Yes, the following sputtering conditions (sputtering gas: Ar + O ₂ , sputtering gas pressure: 0.5 Pa, sputtering gas flow rate: 300 sccm, oxygen concentration in sputtering gas: 1%, leakage magnetic flux density: 400 Gauss, input sputtering power density: 1 W / An ITO sputtering target capable of achieving a nodule coverage ratio (nodule area / erosion part area) of 0.1% when sputtering is performed at cm ² , sputtering time: continuous 20 hours) . 2. The ITO sputtering target according to claim 1, wherein the number of adhered particles is 100 or less.

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