JP5456291B2 - Method for producing sintered sputtering target for forming ITO film - Google Patents

Description

  The present invention relates to a tin oxide powder for an ITO sputtering target, a sintered body sputtering target suitable for forming an ITO film, and a method for producing the same.

An ITO (indium-tin composite oxide) film is widely used as a transparent electrode (film) of a display device centering on a liquid crystal display.
As a method of forming this ITO film, it is usually performed by means generally called physical vapor deposition such as vacuum vapor deposition or sputtering. In particular, the magnetron sputtering method is often used in view of operability and film stability.

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.

A particular problem when forming an ITO film is that protrusions called nodules are generated in the erosion portion of the ITO target or in the vicinity thereof. When this nodule is generated, the sputtering rate is lowered and abnormal discharge (micro arcing) is caused, and the productivity is remarkably lowered.
In addition, due to nodules and abnormal discharge, coarse particles (particles) float in the sputtering chamber and reattach to the generated thin film, causing thin film defects (pinholes) and protrusions. Thus, there arises a problem that the quality of the film is lowered.

As a measure for suppressing the generation of nodules, it is generally known to increase the density of the target and reduce the pores in the target.
In addition, it is effective to reduce variation in composition in the target by refining indium oxide and tin oxide, which are raw material powders of the target sintered body, and increasing their dispersibility. In particular, if the tin oxide grains are coarse, they cannot be sufficiently dissolved in the mixed indium oxide, and are present as a lump of tin oxide in the sintered body, which becomes the starting point of nodules during sputtering. Further, they cause pores in the sintered body and hinder density increase of the sintered body.

  In order to refine the tin oxide powder, the method of mechanically pulverizing the raw material powder is the simplest and the lowest cost. As a pulverizing apparatus, there are a jet mill that pulverizes by mutual collision of raw materials or by colliding with a liner, a bead mill that pulverizes by grinding between media or between liners using a pulverizing medium, and the like. However, in the jet mill method, in order to pulverize a hard and highly cohesive raw material such as tin oxide powder to a particle size in the submicron region, an extreme decrease in the throughput, such as an increase in the number of passes, is caused in terms of cost. Disadvantageous.

For this reason, it is preferable to use a media stirring type pulverizer for the sintering powder of the ITO target, and a wet bead mill that is easy to control the aggregation of the raw materials is optimal.
If the grinding power or the number of passes is increased in this bead mill, the powder will become finer. Therefore, the pulverization is required to be controlled to an appropriate strength.

Indium oxide powder, which is a raw material powder for ITO targets, is easy to grind and does not cause any problems. However, it is harder to grind powders that are hard and cohesive like tin oxide than indium oxide powders. . Therefore, as a raw material powder, pulverization of tin oxide is a problem, and it is necessary to control this.
When tin oxide is pulverized, it can be considered that finer pulverization can be achieved by increasing the pulverization power or the number of passes. However, in addition to the problem caused by increasing the pulverization power or the number of passes, a liner or hard There is a problem that bead materials and the like are mixed in the tin oxide powder as contamination (contaminant).

Therefore, the problem of high density due to sintering using finely divided powder and the contamination of sintered material due to fine graining are contradictory problems. It is the present situation that it cannot be said that is obtained.
In view of the above, it was necessary to obtain a sintered compact target with a uniform component and high density for forming an ITO thin film. There was a problem that the body target was not obtained.

  In the present invention, a tin oxide powder capable of obtaining a sintered body excellent in densification and component uniformity suitable for solving the above-described problems, particularly for forming an ITO thin film, and sintered using the powder. The present invention provides a sputtering target for forming an ITO film and a method for producing the same, thereby reducing a tin oxide-indium oxide target for forming an ITO film that can suppress nodules generated during the formation of the ITO thin film and the accompanying deterioration of the quality of the thin film. It is intended to be provided at a cost.

The technical means for solving the above problems is to strictly control the particle size of the tin oxide powder, and the knowledge that a sputtering target suitable for an ITO transparent conductive film or the like can be obtained thereby. Obtained.
Based on this finding, the present invention is 1) the median diameter determined from the particle size distribution is in the range of 0.40 to 1.0 μm,
And the 90% particle diameter obtained from the particle size distribution is in the range of 3.0 μm or less, and the tin oxide powder for ITO sputtering target 2) The median diameter obtained from the particle size distribution is in the range of 0.40 to 0.60 μm And a tin oxide powder for an ITO sputtering target characterized in that the 90% particle size obtained from the particle size distribution is in the range of 1.0 μm or less 3) A slurry of tin oxide powder with a solid content of 65% or more is wet bead mill The method for producing a tin oxide powder for an ITO sputtering target according to 1) or 2) above, wherein the method is pulverized at a temperature.

In addition, the present invention
4) The median diameter determined from the particle size distribution is in the range of 0.40 to 1.0 μm,
In addition, a sintered sputtering target for forming an ITO film characterized by sintering a tin oxide and indium oxide powder having a 90% particle size in the range of 3.0 μm or less determined from the particle size distribution 5) determined from the particle size distribution ITO characterized by sintering tin oxide and indium oxide powder having a median diameter in the range of 0.40 to 0.60 μm and a 90% particle diameter in the range of 1.0 μm or less determined from the particle size distribution. Sintered sputtering target for film formation 6) A sputtering target for ITO film formation according to 4) or 5) above having a density of 7.12 g / cm ³ or more 7) Solid content of 65% or more The sputter for forming an ITO film according to each of the above 4) to 6), wherein the tin oxide powder slurry is sintered using a tin oxide powder pulverized by a wet bead mill. Manufacturing method of the target.

  It has a remarkable feature that it can obtain a sintered body excellent in high density and uniformity of components suitable for forming an ITO thin film, and as a result, quality degradation, nodules, etc. that occur when ITO sputtering film formation is not uniform It has the outstanding effect that the tin oxide-indium oxide target for ITO film formation which can suppress this abnormal protrusion can be obtained at low cost.

  In the present invention, the tin oxide powder for ITO sputtering target has a median diameter determined from the particle size distribution in the range of 0.40 to 1.0 μm, and the 90% particle diameter determined from the particle size distribution is in the range of 3.0 μm or less. Preferably, the median diameter determined from the particle size distribution is in the range of 0.40 to 0.60 μm, and the 90% particle diameter determined from the particle size distribution is in the range of 1.0 μm or less.

The normal (conventional) tin oxide powder has an integrated volume frequency of 50% obtained from the particle size distribution = median diameter of 1.5 to 2.5 μm, and an integrated volume frequency of 90% obtained from the particle size distribution = 90. The% particle size was in the range of about 5.0 to 10.0 μm.
The tin oxide powder was mixed with indium oxide powder at a predetermined ratio and pulverized to a median diameter of about 0.5 to 1.0 μm by a wet bead mill. However, the tin oxide powder in the mixed powder was not sufficiently dispersed, and some existed as coarse particles of about 5 to 10 μm. Such coarse particles of tin oxide cannot be sufficiently dissolved in indium oxide and cause tin oxide lumps or pores in the sintered body. A sintered body could not be obtained.
In addition, since the components of the sintered body target are not uniform and sufficient density is not obtained in this way, there is a problem that variation occurs during sputtering film formation and the quality of the ITO film is deteriorated. It was.

  As a result of investigating the cause, the particle size of the above tin oxide powder is important, and it is determined from the particle size distribution of the tin oxide powder that the coarse particles contained in the raw material reduce the density of the sintered body. The median diameter is in the range of 0.40 to 1.0 μm, and the 90% particle size determined from the particle size distribution is in the range of 3.0 μm or less, preferably the median diameter determined from the particle size distribution is 0.40 to 0. In the range of .60 μm and the 90% particle size determined from the particle size distribution in the range of 1.0 μm or less, a high-density and high-quality sintered body was successfully obtained.

By using the above powder of the present invention, the preferred density ITO sputtering target 7.12 g / cm ³ or more, it is possible to obtain the sintered body having a 7.13 g / cm ³ or more dense.
During the pulverization, the tin oxide particle size is adjusted by selecting the raw material powder, adjusting the pulverization power, the number of passes, adjusting the diameter and material of the pulverized beads, and adjusting the solid content of the tin oxide powder slurry. It can be performed by appropriately controlling so that the conditions can be achieved.
Although zirconia beads are used as the grinding media, from the problem of zirconium contamination, the problem of contamination can be suppressed as much as possible by using a tin oxide powder slurry having a solid content of 65% or more. This makes it possible to pulverize without difficulty and to obtain a sintered powder having excellent sinterability.

  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 1
A tin oxide powder having a median diameter of 2.0 μm, a 90% particle diameter of 3.50 μm, and a BET specific surface area of 4.0 m ² / g obtained from the particle size distribution was mixed with pure water to prepare a slurry having a solid content of 65%. . For the particle size distribution measurement, a laser diffraction / scattering particle size distribution meter (LA-920 manufactured by Horiba, Ltd.) and a continuous flow surface area meter (SA-6200 manufactured by Horiba, Ltd.) were used for the BET specific surface area. At this time, in order to disperse tin oxide powder in pure water, aqueous ammonia was added to adjust the pH of the slurry to 9.0.

Next, the prepared slurry was pulverized by a bead mill, and pulverized to a median size of 1.0 μm, a 90% particle size of 2.0 μm, and a BET specific surface area of 6.0 m ² / g determined from the particle size distribution. At this time, zirconia beads (YTZ) were used as the ground beads in consideration of wear resistance. The tin oxide slurry pulverized as described above, and indium oxide powder having a median diameter of 2.0 μm, a 90% particle diameter of 3.0 μm, and a BET specific surface area of 8.0 m ² / g determined from the particle size distribution in a solid weight ratio. Tin oxide 1: Indium oxide 9 was mixed in pure water to prepare a slurry with a solid content of 50%.

Next, the prepared tin oxide and indium oxide mixed slurry was pulverized and mixed in a bead mill, and the median diameter determined from the particle size distribution was 0.80 μm, the 90% particle size was 1.50 μm, and the BET specific surface area was 10 m ² / ground to g.
Next, a binder was added to the pulverized slurry, and granulated and dried with a spray dryer. After filling the dry powder into a mold, after molding at a pressure of 1000 kgf / cm ² by a hydraulic press, and further molding under a pressure of 1500 kgf / cm ² with cold isostatic pressing (CIP), the density Of 4.0 g / cc was obtained.
Next, as a result of sintering the molded body in an oxygen atmosphere at a sintering temperature of 1550 ° C. for 4 hours, the density of the obtained sintered body was 7.128 g / cm ³ by Archimedes method. Obtained. However, when the compact was sintered at a sintering temperature of 1500 ° C., the density reached only 7.097 g / cm ³ .

(Example 2)
Under the same grinding conditions as in Example 1 above, the median diameter determined from the particle size distribution was 0.5 μm, the 90% particle size was 0.80 μm, and the BET specific surface area was 7.0 m ² / g.
Next, the pulverized tin oxide slurry, and indium oxide powder having a median diameter of 2.0 μm, a 90% particle diameter of 3.0 μm, and a BET specific surface area of 8.0 m ² / g obtained from the particle size distribution in pure water After mixing, the median diameter was 0.80 μm, the 90% particle diameter was 1.50 μm, and the BET specific surface area was 10 m ² / g in the same manner as in Example 1.

The pulverized slurry was granulated and dried in the same manner as in Example 1. After then obtained powder was filled in a mold, after molding at a pressure of 1000 kgf / cm ² by a hydraulic press at more cold isostatic pressing (CIP) molding at a pressure of 1500 kgf / cm ² Thus, a molded body having a density of 4.0 g / cc was obtained.
Next, as a result of sintering the molded body in an oxygen atmosphere at a sintering temperature of 1550 ° C. for 4 hours, the density of the obtained sintered body was 7.129 g / cm ³ by Archimedes method. Obtained. Furthermore, when the compact was sintered at a sintering temperature of 1500 ° C., a high-density sintered body having a density of 7.130 g / cm ³ was obtained.

(Comparative Example 1)
The median diameter determined from the particle size distribution is 2.0 μm, the 90% particle size is 3.50 μm, the tin oxide powder has a BET specific surface area of 4.0 m ² / g, and the median diameter determined from the particle size distribution is 2.0 μm, 90 An indium oxide powder having a% particle size of 3.0 μm and a BET specific surface area of 8.0 m ² / g was mixed with pure water in the same manner as in the example so that the weight ratio of solid content was tin oxide 1: indium oxide 9. A slurry with a solid content of 50% was prepared.

Next, in the same manner as in Example 1, the median diameter determined from the particle size distribution was pulverized to 0.80 μm, the 90% particle size was 1.50 μm, and the BET specific surface area was 10 m ² / g.
A binder was added to the pulverized slurry, and granulated and dried by the same method as in Example 1. The resulting powder was filled in a mold, after molding at a pressure of 1000 kgf / cm ² by a hydraulic press, and further molding under a pressure of 1500 kgf / cm ² with cold isostatic pressing (CIP), A molded body having a density of 4.0 g / cc was obtained.

Next, as a result of sintering the molded body in an oxygen atmosphere at a sintering temperature of 1550 ° C. for 4 hours, the density of the obtained sintered body reached only 7.101 g / cm ³ by Archimedes method. Even when the sintering temperature was increased to 1650 ° C., the density of the sintered body was 7.108 g / cm ³ .
The sintered bodies produced in Examples 1 and 2 and Comparative Example 1 are machined to produce a sputtering target, and the amount of nodule generation (coverage) during sputtering and the number of abnormal discharges (micro arcing) during sputtering. Was measured.

The sputtering conditions are as follows.
Target size: 127 x 508 x 6.35 mm
Sputtering gas: Ar + O ₂
Sputtering gas pressure: 0.5Pa
Sputtering gas flow rate: 300 SCCM
Oxygen concentration in sputtering gas: 1 Vol%
Leakage magnetic flux density: 0.1T
Sputtering was started at an input sputtering power density of 0.5 W / cm ² , and the film formation rate was increased to keep constant.
Sputter integrated power: ~ 160 WHr / cm ²

 FIG. 1 shows the amount of nodule generation, and FIG. 2 shows the number of micro arcing. The nodule generation amount (coverage) was calculated as a value obtained by binarizing the image of the erosion portion of the target with a computer and dividing the generated nodule area by the erosion area. The threshold for micro arcing was set to detection voltage: 100 V or more, emission energy (sputtering voltage when arc discharge is occurring × sputtering current × generation time): 10 mJ or less.

As apparent from FIG. 1, the target of the comparative example sharply nodules increases from the integrated power 40WHr / cm ^2, has a cumulative power 160WHr / cm ² in 40% of nodules coverage is life end On the other hand, it can be seen that the targets of Examples 1 and ² have a nodule generation amount of 0% even when sputtering is performed up to an integrated power of 160 WHr / cm ² , which is remarkably excellent.

Further, in the micro arcing frequency of FIG. 2, the target of the comparative example suddenly increased the arcing frequency from the integrated power of 80 WHr / cm ² , whereas the targets of Examples 1 and 2 were stable with a small number of arcing throughout. It can be seen that film formation conditions can be obtained.
When compared in Examples 1 and 2, no difference was found in the amount of nodule generation, but it can be seen that Example 2 is superior when compared in terms of the number of arcing.

(Example 3)
The amount of contamination (impurities) of the zirconia beads when producing the tin oxide powder used in Examples 1 and 2 was examined. For the pulverization, the bead mill used in the above examples was used, and the crushed beads were Zr beads (YTZ) having a diameter of 0.5 mm.
The tin oxide powder was mixed with pure water so that the solid weight ratio would be 25%, 45%, and 65%, respectively. At this time, in order to disperse tin oxide powder in pure water, aqueous ammonia was added to adjust pH to 8.0 to 10.0, and the viscosity of the slurry was adjusted to 0.1 Pa · s or less.
Each solid content slurry was subjected to a pass operation under the same pulverization conditions, and each pulverized particle size and the amount of mixed Zr were investigated. As a result, as shown in FIG. 3, it was found that the amount of mixed Zr was smaller as the solid content was higher when compared with the same particle size.

  It has the remarkable feature that a sintered body with high density and excellent uniformity of components can be obtained, and this suppresses deterioration of quality and abnormal projections such as nodules that occur when ITO sputtering film formation is not uniform. Since it has the outstanding effect that the tin oxide-indium oxide target for ITO film formation which can be obtained can be obtained at low cost, it is useful for ITO film formation.

It is a figure which shows sputter | spatter integrated power and a nodule coverage at the time of the sputtering of the sputtering target produced in Example 1, 2 and the comparative example. It is a figure which shows the sputter | spatter integrated power and the number of times of micro arcing at the time of the sputtering of the sputtering target produced in Example 1, 2 and the comparative example. It is a figure which shows the median diameter and Zr contamination amount in each solid content density | concentration of the tin oxide powder slurry produced in Example 3. FIG.

Claims (4)

The solid weight ratio of 65% or more of tin oxide powder slurry was milled using zirconia beads as grinding media, (excluding 0.40) median diameter of 0.40 obtained from the particle size distribution ~1.0μm And producing a tin oxide powder having a 90% particle size of 3.0 μm or less determined from the particle size distribution, and mixing, forming and sintering the tin oxide powder and the indium oxide powder. A method for producing a sintered sputtering target for forming an ITO film made of tin oxide and indium oxide, characterized by having a density of 7.12 g / cm ³ or more. ^{2. The} method for producing a sintered sputtering target for forming an ITO film according to claim 1, wherein the nodule coverage is 0% at an accumulated electric power of 50 WHr / cm ² . The nodule coverage is calculated by binarizing an image of the erosion portion of the target with a computer and dividing the area of the generated nodule by the erosion area. Nodule coverage, 0% in cumulative power amount 50WHr / cm ^2, the production of an ITO film forming sintered sputtering target according to claim 1, wherein the at integrated electricity 160WHr / cm ² is less than 40% Method. ^{2. The} method for producing a sintered sputtering target for forming an ITO film according to claim 1, wherein the nodule coverage is 0% at an integrated electric energy of 160 WHr / cm ² .