JPH07100852B2 - ITO sputtering target - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a target used when forming an ITO film (Indium-Tin Oxide film) by sputtering.

[0002]

2. Description of the Related Art In ₂ O ₃ and SnO ₂ oxide films, which have "n-type conductive semiconductor characteristics" called "ITO film", have very high conductivity and high visible light. Since it also has light transparency (transparency), liquid crystal display devices, thin film electroluminescence display devices, radiation detection elements, transparent tablets for terminal equipment, and heat generation films for preventing dew condensation on window glass are utilized by taking advantage of these characteristics. , Is used for a wide variety of applications such as antistatic films or selective permeation films for solar collectors. As a method for forming this ITO film, a chemical film forming method such as a spray method or a CVD method utilizing thermal decomposition of a compound, or a physical film forming method such as a vacuum vapor deposition method or a sputtering method is known. In particular, recently, it is possible to form a large area and to form a low resistance film with good reproducibility.
As the advantages of “sputtering method” have been attracting attention, the adoption of the “sputtering method” is spreading.

By the way, when an ITO film is formed by a sputtering method, a sputtering target made of indium oxide and tin oxide (hereinafter abbreviated as "ITO target") is used. As a get, a powder mixture of indium oxide and tin oxide, or a powder mixture obtained by adding dopant to the powder mixture is press-molded at room temperature, and the compact is sintered at 1250 to 1650 ° C. in the atmosphere. Further, those which have been further machined have been generally used.

However, the ITO manufactured by the above method (method of performing mechanical processing after cold press air sintering)
(A) Abnormal discharge called arcing occurs during sputtering, which often impairs the stability of film forming operation. (B) There is a large amount of gas adsorbed on the surface of the get ", which deteriorates the film quality. (C) Even if the sputtering device takes special leak prevention measures, the transparency of the formed ITO film tends to deteriorate. However, it has been pointed out that it is difficult to stably secure a good film quality, and so on. Therefore, it is possible to obtain better results in terms of "sputtering workability" and "formed ITO film quality". The target was strongly desired.

In recent years, of the series of steps for producing a sintered target, a method in which hot pressing is applied to the "molding step of powder raw material" (hereinafter referred to as "hot pressing method").
However, the ITO target obtained by sintering by this method and subjected to machining does not show much remarkable improvement in the above problems. Furthermore, (a) the initial cost of the equipment will rise, and it will be difficult to upsize the equipment. (B) Since the mold and the like will be expensive, the running cost will increase, and (c) one operation Since it takes a long time, mass production is inferior, new manufacturing problems occur, and these eventually affect the target price, so it is hard to say that it is industrially satisfactory.

In view of the above, the object of the present invention is to solve the above-mentioned problems pointed out in the conventional materials, to minimize abnormal discharge during sputtering, the amount of adsorbed gas, etc.
It was an object to provide an ITO sintered target on which a high quality ITO film having sufficiently excellent transparency is stably formed at low cost.

[0007]

Means for Solving the Problems The inventors of the present invention conducted experiments and research from various viewpoints in order to achieve the above-mentioned object, and found that "the factors affecting the characteristics of the ITO sintered target are Among various types, the nitrogen content in the target is “transparency of the formed ITO film”, “etching property”, “heat resistance”, “abnormal discharge” during sputtering, and “target”. The effect on the "gas adsorption amount" is very large, and if the nitrogen content can be suppressed below a specific value, the above-mentioned problems pointed out in the ITO sintered target will be remarkably improved. " I got it.

However, in reality, a technique for industrially mass-producing an ITO sintered target in which the nitrogen content is suppressed to such an extent that the above-mentioned good characteristics are ensured has not been established yet. It was the current situation. That is, in the "conventional ITO sintering target" obtained by cold-press air sintering or hot-pressing and mechanical processing, even if it is obtained by careful operation, it does not contain nitrogen. The rate did not fall below 7 ppm. This has a limit in reducing the closed pores (holes in the target which are not open to the outside) generated in the "obtained ITO sintered target" in the above-mentioned conventional method, and therefore the black -It was considered that the content of nitrogen, which is apt to be included in sudpore, was inevitably high.

However, the remarkable improvement effects in terms of the transparency of the ITO film, the etching characteristics, the stability of heat resistance, the abnormal discharge during sputtering, the prevention of gas adsorption, and the like are recognized. Is in the range of 5 ppm or less, and no industrial means has been known for keeping the nitrogen content of the ITO sintered target in such a fine range.

Therefore, the inventors of the present invention continued their research to find a means for stably producing an ITO sintered target on an industrial scale in which the closed pores, which particularly affect the nitrogen content, are minimized. We were able to obtain new knowledge as shown in. a) In the production of ITO sintered target, "sintering of compression-molded oxide powder mixture" is carried out in a high oxygen partial pressure atmosphere of 1 atm or more, and this is subjected to machining according to a conventional method. And, even when the cold pressing method is applied to the compression molding of the oxide powder mixture, the "ITO sintered target" having the extremely small nitrogen content and the extremely low nitrogen content is stably secured. In addition to suppressing abnormal discharge and gas adsorption amount during sputtering,
Sufficiently suppress the decrease in transparency of the ITO film, the variation in etching characteristics, and the decrease in heat resistance due to "mixing of black indium nitride (InN) generated by the reaction of nitrogen contained in the get with indium during sputtering". Is possible.

B) In addition, when the "ITO target" is sintered in a high oxygen partial pressure atmosphere, the "ITO target" obtained by the phenomenon of the closed pores described above is obtained. The density of 7 g / cm ³ or more (theoretical density 9
Since it can be increased up to about 7 to 99% (the one obtained by the conventional cold press atmospheric sintering method has a density of 4.
The density is 2 to 5.8 g / cm ³ , which is at most 60 to 80% of the theoretical density, and even the density obtained by the conventional hot pressing method is 6.
0 to 6.7 g / cm ³ , which is about 83 to 93% of the theoretical density),
In addition to the realization of a wide density range of "ITO sintered target", the high density product as described above enables "IT
Further improvements in the above properties desired for "O-sintered target" are possible.

C) However, in order to improve the above-mentioned various characteristics, I
Needless to say that the nitrogen content of the TO sintered target and the density itself of the material itself are deeply related, but the bulk resistance value is also closely related, and the density of the material and the bulk resistance value are closely related to each other. When adjusted to a specific region, the stability of the film forming operation is further improved, and the formability of the high performance ITO film is further improved.

[0013] The present invention has been completed based on the above findings matters, "the amount of nitrogen contained with 5ppm or less, and the density D (g / cm ³⁾
And bulk resistance ρ (mΩcm) is a) 6.20 ≤ D ≤ 7.23, b) -0.0676D + 0.887 ≥ ρ ≥ -0.0761D + 0.66
6, "ITO target produced by powder metallurgy from raw materials mainly composed of indium oxide and tin oxide", which satisfies the following two formulas at the same time, provides transparency under stable sputtering work. It is important to know how to efficiently form a high quality ITO film.

In the present invention, the reason why the "nitrogen content", "density D" and "bulk resistance value ρ" of the ITO sintered target are limited to the above ranges is as follows. (A) Nitrogen content rate The nitrogen content rate of the ITO sintered target is greatly affected by the nitrogen content in the closed pores contained in the target, but if the content rate exceeds 5 ppm, abnormalities during sputtering will occur. Not only can the discharge and the amount of gas adsorbed on the target surface not be sufficiently suppressed, but as described above, the contained nitrogen and indium react with each other during sputtering to generate black indium nitride (InN), and the ITO film. decrease in transparency mixed in, bar etching characteristics variability, the phenomenon of reduced heat resistance becomes remarkable. Therefore, the nitrogen content is limited to 5 ppm or less. Nitrogen content: 5ppm
The following "ITO sintering target" is as described above.
It can be manufactured by sintering the compression-molded raw material oxide powder mixture in a high oxygen partial pressure atmosphere of 1 atm or more (oxygen atmosphere sintering method).

(B) Density D and bulk resistance value The density D of the ITO sintered target is also the workability of sputtering (generation of abnormal discharge, deposition rate, deposition rate stability, gas adsorption on the target surface). It has a considerable effect on the amount) and the film quality, but it is also closely related to the bulk resistance value, so it is desirable to adjust it appropriately. When the density D of the target is less than 6.20 g / cm ³ , the above-mentioned characteristics start to be adversely affected, while the density of the ITO sintered target is increased to a region exceeding 7.23 g / cm ³ . Is very difficult even by the "sintering method in an oxygen atmosphere", which causes a cost disadvantage.
Therefore, the density of ITO sintered target is 6.20 ~ 7.23g / cm.
^It is desirable to adjust to ³ .

Bulk resistance value ρ of ITO sintered target
Has a tendency to largely depend on its density D, and, for example, as shown in FIG. 1, tends to decrease sharply as the density increases. The lower the bulk resistance value is, the less the abnormal discharge is generated during sputtering, which is preferable. However, achieving ρ <−0.0761D + 0.666 in the region of the density of 6.20 to 7.23 g / cm ³ means “burning in an oxygen atmosphere”. It's also very difficult to do by law. On the other hand, if the bulk resistance value ρ of the ITO sintered target is in the region of ρ> -0.0676D + 0.887, abnormal discharge will occur frequently during sputtering, and the stability of the film formation operation will be impaired. The phenomenon that the speed becomes unstable and the film forming speed decreases as the sputtering progresses becomes remarkable. Therefore, it is desirable to adjust the bulk resistance value ρ of the ITO sintered target within the range of −0.0676D + 0.887 ≧ ρ ≧ −0.0761D + 0.666. The relationship between the "density" and the "bulk resistance" of the "ITO sintered target" according to the present invention is shown in a graph of FIG.

The control range of nitrogen content, density and bulk resistance of the ITO sintered target according to the present invention is as follows.
It is possible to further expand by adjusting not only the raw material powder but also the press pressure when press-forming the raw material powder, the atmosphere (oxygen partial pressure) at the time of sintering, the sintering temperature and the like.

As described above, the ITO sintering target according to the present invention is obtained by press-molding and sintering a powder mixture containing indium oxide and tin oxide as main components as in the conventional method. When manufacturing an ITO target, the sintering is performed as "1.
Pure oxygen gas atmosphere pressurized above atmospheric pressure (absolute pressure) ","
It is obtained by carrying out in a pressurized oxygen atmosphere such as a mixed gas atmosphere having an O ₂ partial pressure of 1 atm or more.
The reason why the above product with good performance can be obtained by applying a pressurized oxygen atmosphere in the sintering step is not yet clear at present.

However, the fact that "when sintering is carried out in an atmosphere of an inert gas such as N ₂ or Ar, the ITO is decomposed to lower the density and performance," and the atmosphere However, since ITO has a property of easily dissociating oxygen when heated to a high temperature, dissociation of ITO due to high temperature heating is effectively prevented by pressurizing oxygen during sintering, and oxygen is a sintering aid. It is speculated that it may contribute to the suppression of closed pores, the increase in density due to these factors, and the decrease in bulk resistance. Further, the sintering temperature in the pressurized oxygen atmosphere is appropriately about 1600 to 1700 ° C. as in the case of conventional atmospheric sintering, and the sintering time is preferably 3 hours or more (sintering time Is the longer the better the result).

Next, the present invention will be described more specifically by comparing the present invention with comparative examples.

EXAMPLE First, tin oxide powder having the same particle size as that of indium oxide powder having an average particle size of 2 μm was uniformly mixed in a weight ratio of 90:10, and a binder for molding was added thereto, and -For Ludopress, the mold (165 ^W x 52
0 ^L ), graphite type (23
0φ) was uniformly filled. Then, according to the following steps, "Invention product 1", "Invention product 2", "Comparative product 3: Co-
And an ITO sintered target of "Comparative product 4: Hot pressed product".

The product of the present invention 1: The raw material mixed powder filled in the mold is 800 kg / c by a hydraulic press.
After pressurizing with m ² pressure, this is heated to 80 ° C. to evaporate the water content in the binder to dry, and then in a pressure sintering furnace into a pure oxygen gas atmosphere of 1.5 atm (absolute pressure). 1
Sinter at 650 ° C for 9 hours. Next, the surface of the obtained sintered body was ground with a surface grinder, and the side edges were cut with a diamond cutter to obtain a target product. The nitrogen content of the ITO sintered target product thus obtained was 1 ppm.
Below (lower limit of detection: 1 ppm), the density was 6.90 g / cm ³ , and the bulk resistance value was 0.15 mΩcm.

Inventive product 2: Raw material mixed powder filled in a die is pressed by a hydraulic press at 950 kg / c.
After pressurizing with m ² pressure, it is heated to 80 ° C. to evaporate the water content in the binder to dry it, and then in a pressure sintering furnace into a pure oxygen gas atmosphere of 3.5 atm (absolute pressure). 1
Sinter at 650 ° C for 9 hours. Next, the surface of the obtained sintered body was ground with a surface grinder, and the side edges were cut with a diamond cutter to obtain a target product. The nitrogen content of the ITO sintered target product thus obtained was 1 ppm.
, The density was 7.23 g / cm ³ , and the bulk resistance value was 0.12 mΩcm.

Comparative product 3 (cold press air-sintered product): Raw material mixed powder filled in a mold is hydraulically pressed at 950 kg / c.
After pressurizing with a pressure of m ² , this is heated to 80 ° C. to evaporate the water content in the binder and dried, and then sintered in air at 1650 ° C. for 10 hours. Next, the surface of the obtained sintered body was ground with a surface grinder and the side edges were cut with a diamond cutter to obtain a target product. The obtained ITO sintered target product had a nitrogen content of 36 ppm and a density of 5.54.
The g / cm ³ and the bulk resistance value were 0.84 mΩcm.

Comparative product 4 (hot-pressed product): A graphite mold was filled with a raw material mixed powder which was heated at 80 ° C., dried and cooled, and a pressure was 300 kg / c in an Ar atmosphere.
Sintering was performed by hot pressing under the conditions of m ² , heating temperature: 900 ° C., pressure heating time: 1 hour. Next, the surface of the obtained sintered body was ground with a surface grinder, and the side edges were cut with a diamond cutter to obtain a target product. The ITO sintered target product thus obtained had a nitrogen content of 7 ppm, a density of 6.42 g / cm ³ , and a bulk resistance of 0.60 mΩ.
It was cm.

Next, using these targets, an ITO film formation test was conducted under the following conditions by an in-line type sputtering machine, and the film formation condition at that time was investigated. Sputter power: 1.2 W / cm ² , gas pressure: 5 × 10 ⁻³ Torr, O ₂ composition: 1%. The test results are summarized in Table 1.

[0026]

[Table 1]

Note that the "decrease in transparency" in Table 1
In addition, the film thickness is 1500Å on the 1.1mm thick glass substrate.
Of the ITO film at the wavelength of 550 nm.
After measuring the transmittance (value including the glass substrate), its value
The one in which the poppy rank content and subjective judgment. Also,
"Abnormal discharge count" in Table 1 indicates the sputter operation
9th batch with continuous discharge for about 20 hours as one batch
Number of abnormal discharges that occurred in 1 hour during the 10th to 11th hour
Is measured for each sample. The results shown in Table 1 also show that the film forming workability of the "invention product" is better than that of the "comparative product (cold press air-sintered product, hot press product)". It is clear below that a high quality ITO film with excellent transparency can be formed.

[0028]

[Summary of Effects] As described above, according to the present invention, it is possible to provide an inexpensive ITO sintered target which is excellent in sputtering performance and which can provide an ITO film having high transparency. Can be used to form an excellent ITO film on the substrate with good workability and stability.
It has an extremely useful effect on the industry.

[Brief description of drawings]

FIG. 1 is a graph showing a change tendency of bulk resistance with respect to the density of an ITO sintered target.

FIG. 2 is a graph showing the relationship between the density and bulk resistance of the ITO sintered target according to the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-207858 (JP, A) JP-A-3-150252 (JP, A) JP-A-2-297812 (JP, A) JP-A-2- 297813 (JP, A)

Claims (1)

[Claims] 1. An ITO sputtering target produced by powder metallurgy from raw materials containing indium oxide and tin oxide as main components, wherein the amount of nitrogen contained is 5 ppm or less and the density D (g / cm ³ ) And the bulk resistance value ρ (mΩcm) simultaneously satisfy the following two equations. a) 6.20 ≤ D ≤ 7.23, b) -0.0676D + 0.887 ≥ ρ ≥ -0.0761D + 0.66
6.