JPH058532B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a sputtering target containing In ₂ O ₃ as a main component and used for forming a transparent conductive film used in an image pickup tube or the like.

[Background of the invention]

The photoelectric exchange part of an image pickup tube, especially a photoconductive type image pickup tube, is
It has a structure in which a photoconductive film is formed on a transparent glass substrate via a transparent conductive film. In such a photoelectric exchange unit, even if there is a slight electrical or optical defect within the effective surface, it will cause bright spot defects, so-called white flaws, and black dot defects, so-called black flaws, on the image capture and playback screen. Needless to say, the existence of defects is highly avoided. Although this is true for all image pickup tubes to varying degrees, defects in the transparent conductive film can cause defects in the rectifying film, especially in blocking types that have rectifying contact at the interface between the transparent conductive film and the photoconductive film. Since this often means destruction and the white flaws are very noticeable, it was necessary to pay close attention to the formation of the transparent conductive film. The applicant has previously proposed that the density of the target material, that is, the ratio of the apparent specific gravity to the pure specific gravity of the constituent materials, be 80% or more as a method for forming a transparent conductive film with few defects. As a sputtering target, it is desired that the produced film has few defects and that the film production efficiency is high.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to provide a sputtering target for forming a transparent conductive film that can form a transparent conductive film with few defects with high productivity. .

[Summary of the invention]

In order to achieve this purpose, the present invention has a density of 80% or more, and each 300 cm ²
It has a structure in which unit targets having the following surface areas are aligned and bonded to an electrode plate so that they overlap each other with side surfaces inclined at 30 to 60 degrees with respect to the main surface.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail using specific data.

Generally, the formation of a transparent conductive film by sputtering using a target mainly composed of In ₂ O ₃ is as follows:
Specifically, a sintered body made of sintered powder of oxides such as In ₂ O ₃ , SnO ₂ , CdO, etc. is used as a target body, and Ar or, in some cases, H ₂ , O ₂ , H ₂ This process is carried out in an atmosphere containing oxygen, etc., and when we analyzed the components of the defects in the transparent conductive film that are a problem with this method, we found a considerable proportion of granules that were presumed to have collapsed and scattered from the sintered target body. It was done.

The sintered density of the sintered target can be changed by changing the manufacturing conditions of the material powder, particle size distribution adjustment, molding conditions and methods, and sintering conditions and methods, but the higher the density is to a certain extent, the more likely the particles will collapse as described above. It is presumed that there is a tendency to suppress this, and from this point of view, we investigated the relationship between the density of the target body and the number of foreign particles per 1 cm ² of transparent conductive film.
As shown by curve A in FIG. 1, it was found that as the density of the target body increased, the number of defects on the surface of the formed transparent conductive film was drastically reduced.

On the other hand, as a desirable performance as a target,
As mentioned above, in addition to the absence of particle collapse, the workability is also good, and in relation to this workability, the gas gushing characteristics from the target body were also found to be related to the density. . In other words, curve B in Figure 1 is a measure of the gas gushing characteristics, and indicates a vacuum level of 5 x 10 ^-6 Torr, which allows sputtering work to begin after the target body is attached to the sputtering device and exhaust is started. This is the measurement of the evacuation time. When performing the first sputtering operation after target fabrication, the evacuation time tends to be longer due to the influence of adsorbed gas, so this influence is excluded, but as is clear from the figure, 70% The degree of vacuum rises quickly for low-density targets and high-density targets that do not exceed 80%, but is extremely slow in the intermediate region of around 75%. This can be explained, for example, by the following mechanism. That is,
When observing the surface of a sintered target with a scanning electron microscope, it can be seen that in a low-density target, constituent fine particles of various sizes are piled up, and the voids between the particles are considered to have a labyrinth structure of various sizes. As the density increases, large voids first disappear, but no particular change is observed in the number of voids themselves.

As the density increases further, the number of such voids begins to decrease significantly. As a result, the gas that is believed to have been occluded in the voids within the target oozes out in such a large amount and so slowly that the pumping speed of the vacuum pump cannot keep up. It is presumed that for this reason, the degree of vacuum increases slowly. As the density increases further to 80% or more, the number of voids begins to decrease dramatically. When the target surface in this state is observed with an electron microscope, the powder particles in the target structure are fused together, and there are no grain agglomerates like those observed when the density is low, and the few voids are fine particles due to particle fusion. , formed like a pinhole in a dense network structure. It is presumed that the degree of vacuum is improved in a high-density target due to such a drastic reduction in voids and the network structure.

Additionally, as the target density increases, the color tone of the target tends to shift from bright yellow-green to greenish-brown black, depending on the sintering method. Although it is presumed that this is due to reduction, there is almost no difference in the electro-optical properties of the transparent conductive films formed with these target bodies, and no tendency for changes in the granularity and crystallinity of the films has been observed. I couldn't help it.

As a result, it is found that it is suitable to use a target with a density of 80% or more to form a transparent isoelectric film that does not allow even the presence of extremely fine foreign substances, such as those used in image pickup devices.

However, when a transparent conductive film is generally formed by sputtering, it is desirable to enlarge the target size and enlarge the inside of the vacuum apparatus in order to form the film on the film formation substrate with good productivity. In many cases, materials such as ``x 15'' x 1/4'' (thickness) are used. However, for high-density targets such as those mentioned above, powder materials such as In ₂ O ₃ and SnO ₂ are pressed at high temperature and high pressure. In order to produce plate-shaped compacts, the amount of compression per unit area is extremely large, ranging from several thousand kilograms to one ton.
Because it is necessary to carry out the process at a high temperature of 10,000℃ or more,
A plate-shaped target with a relatively small surface area of 300 cm ² or less can be manufactured by optimizing the manufacturing conditions, but it is difficult to form a large-area target as described above in one piece.

Therefore, in the present invention, as shown in FIG.
A plurality of high-density targets 1 with a small size of cm ² or less are made, cut and shaped, and sputtered into an electrode plate 2.
This problem was solved by creating a bonded structure with aligned alignment and bonding using an organic adhesive or a low-melting metal material to achieve the desired area. In this case, it is necessary to prevent gaps from forming between the bonded unit targets. This is because if there is a gap, the bonding material 3 and electrode plate 2 (usually made of an oxygen-free copper plate with good thermal conductivity) will be sputtered during film formation by sputtering, resulting in a transparent film with good properties. This is because a conductive film cannot be obtained, but in order to eliminate this gap, in the present invention, as shown in the figure, the cut side surfaces where each unit target 1 joins each other are sloped so that each target partially overlaps. I have to. At this time, if the cut surfaces are made to fit together in a complicated shape, the high-density target, which is mainly composed of In ₂ O ₃ , is hard and brittle, so it is likely to break during cutting or cause cracks or cracks during bonding. However, as shown in the figure, the angle θ to the main surface of the cut side to be joined is set to 30
This can be prevented by keeping the temperature at ~60 degrees. At this time, if the joints on the cut sides are brought close together without any gaps, the edges may be damaged, but if the structure is as described above, even if there is a gap of 0.05 to 0.8 mm between the joint surfaces, the formed film will be It has the advantage of not having any characteristics. However, since the target is used repeatedly, the target wears out, and the bonding material on the bonding surface during wear may affect the properties of the produced film. As a result of experiments conducted by the inventors, the preferred gap for the joint surface considering the above-mentioned details is
It was 0.05-0.5mm.

The number of unit targets 1 to be bonded together can be greater, but in consideration of ease of bonding, susceptibility to breakage when targets are worn out by spatter, etc., it is desirable that the number be within eight.

〔Effect of the invention〕

As explained above, according to the sputtering target of the present invention, the density is set to 80% or more, and unit targets of 300 cm ² or less are overlapped with each other with side surfaces inclined at 30 to 60 degrees with respect to the main surface. By adopting a structure in which the film is bonded to an electrode plate in this manner, it becomes possible to form a transparent conductive film with few defects with high productivity.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the target density, the number of foreign particles in the produced film, and the evacuation time, and FIG. 2 is a sectional view showing an embodiment of the present invention. 1... Unit target, 2... Electrode plate, 3...
bonding material.

Claims (1)

[Claims] 1. In a sputtering target for forming a transparent conductive film containing In ₂ O ₃ as the main component, the main surface is a unit target whose ratio of apparent specific gravity to the pure specific gravity of the constituent materials is 80% or more and each has a surface area of 300 cm ² or less. 1. A sputtering target for forming a transparent conductive film, characterized by having a structure in which inclined side surfaces having an angle of 30 to 60 degrees with respect to the target are aligned and bonded to an electrode plate so as to overlap with each other.