JP6067028B2 - Method for producing zinc oxide based sputtering target - Google Patents

Description

  The present invention relates to a method for producing a zinc oxide based sputtering target.

  ITO (indium tin oxide) or the like has been widely used for many years as a transparent conductive film used for electronic devices and the like. Moreover, it is industrially mainstream that the production of the transparent conductive film is performed by sputtering.

  However, in light of the recent increase in the price of rare metals such as indium, a transparent conductive material that substitutes for ITO is strongly desired. As a promising candidate for such a transparent conductive material, a zinc oxide film having high transparency and conductivity has attracted attention. In order to improve the electrical conductivity of the zinc oxide film, it is important to suppress arcing during sputtering. For this purpose, it is necessary to improve the density and electrical conductivity of the target.

  Patent Document 1 (Patent No. 4661948) discloses a method for producing a zinc oxide-based sputtering target using γ-alumina as a dopant material, and has a high density through pressure sintering in a hot press apparatus. It has been reported that a zinc oxide-based sputtering target having a low specific resistance has been obtained.

Japanese Patent No. 4661948

  The present inventors can manufacture a high-density and low-resistance zinc oxide-based sputtering target by using alumina and / or boehmite having a large specific surface area as a dopant material and sintering at a predetermined temperature or higher. And gained knowledge.

  Accordingly, an object of the present invention is to produce a high density and low resistance zinc oxide based sputtering target.

According to one aspect of the present invention, a step of adding a dopant material containing alumina and / or boehmite having a specific surface area of 40 to 200 m ² / g to zinc oxide powder to obtain a mixed powder;
Molding the mixed powder to obtain a molded body;
Sintering the molded body at a temperature of 1300 ° C. or higher to obtain a zinc oxide-based sputtering target;
The manufacturing method of the zinc oxide type | system | group sputtering target which comprises this is provided.

2 is a SEM photograph of θ-alumina used in Example 1. 2 is a SEM photograph of boehmite used in Example 2. 4 is a SEM photograph of γ-alumina used in Example 3. 2 is a SEM photograph of α-alumina used in Example 11.

TECHNICAL FIELD The present invention zinc oxide-based sputtering target is the production method of the zinc oxide-based sputtering target. The zinc oxide-based sputtering target is composed of a zinc oxide sintered body that includes zinc oxide crystal particles. That is, the zinc oxide sintered body is a solid in which countless zinc oxide crystal particles are bonded to each other by sintering. Zinc oxide crystal particles are particles composed of zinc oxide, and may contain a dopant such as Al and inevitable impurities as other elements. Such other elements may be substituted with hexagonal wurtzite structure Zn sites or O sites, may be included as additive elements that do not constitute a crystal structure, or exist at grain boundaries. It may be a thing. The zinc oxide sintered body may also contain other phases or other elements as described above in addition to the zinc oxide crystal particles, but preferably comprises zinc oxide crystal particles and inevitable impurities.

In the method according to the present invention, first, a mixed material is formed by adding a dopant material containing alumina and / or boehmite having a specific surface area of 40 to 200 m ² / g to zinc oxide powder to obtain a compact. Alumina and / or boehmite is an Al source for introducing Al as a dopant into zinc oxide. And a molded object is sintered at the temperature of 1300 degreeC or more, and a zinc oxide type | system | group sputtering target is obtained. Thus, by using alumina and / or boehmite with a large specific surface area as a dopant material and sintering at a predetermined temperature or higher, a high-density and low-resistance zinc oxide-based sputtering target can be obtained. The reason why low resistance can be obtained by this method is not clear, but the combination of the use of an active Al source with a large specific surface area and firing at a high temperature (1300 ° C. or higher) causes the zinc oxide crystal particles to become coarse and oxygen It is presumed that this is because the number of grain boundaries, which tend to be high in resistivity due to segregation, can be reduced. In any case, by performing sputtering using such a high-density and low-resistance zinc oxide-based sputtering target obtained by the present invention, a low-resistance sputtered film can be produced while suppressing arcing during sputtering. Is possible.

  Hereafter, each process of the method of this invention is demonstrated concretely.

(1) Preparation of mixed powder A predetermined dopant material is added to zinc oxide powder to obtain mixed powder. The mixing method of the zinc oxide powder and the dopant material is not particularly limited, but is preferably performed by ball milling. A preferred ball mill treatment is a wet ball mill treatment performed using a solvent such as ethanol. The slurry obtained through the wet ball mill treatment is preferably mixed powder having a desired particle size distribution through drying with an evaporator or the like and passing through a mesh.

Zinc oxide powder is can be not particularly limited the use of zinc oxide powders of commercially available various, specific surface area preferably has 1 to 50 m 2 / ^g, more preferably at 2~40m 2 / ^g Yes, more preferably 3 to 30 m ² / g.

Dopant material has a specific surface area of 40 to 200 m ² / g, made preferably 50~180m ² / g, more preferably comprises alumina and / or boehmite 70~150m ² / g. Alumina and / or boehmite is preferably at least one selected from the group consisting of θ-alumina, γ-alumina and boehmite from the viewpoint of ensuring a specific surface area within the above range, more preferably θ-alumina. is there. Alumina and / or boehmite having a specific surface area within the above range typically comprises mainly fine particles having a particle size of 100 nm or less. For example, 90% by mass or more of all particles of alumina and / or boehmite is 100 nm or less. Having a particle size of The amount of alumina and / or boehmite added is not particularly limited as long as the desired characteristics as a zinc oxide-based sputtering target are obtained, but is preferably 0.1 to 5% by mass with respect to the total amount of the mixed powder, More preferably, it is 1-3 mass%.

  The dopant material may further contain other dopant components such as gallium oxide, indium oxide, tin oxide, and titanium oxide in addition to the alumina and boehmite, and the content thereof is desired as a zinc oxide based sputtering target. As long as the above characteristics are obtained, there is no particular limitation.

(2) Molding step The mixed powder is molded into a molded body. This molding step preferably includes press molding, and more preferably is performed by press molding and subsequent isostatic pressing. By accompanying such a press, it becomes easy to obtain a high density and low resistance zinc oxide-based sputtering target. Pressure isostatic pressing is preferably 0.5 t / cm ² or more, more preferably 1~10t / cm ^2.

(3) Sintering process A molded object can be sintered at the temperature of 1300 degreeC or more, and a zinc oxide type | system | group sputtering target can be obtained. This sintering step is preferably performed by holding the compact at a temperature of 1300 ° C. or higher for 2 hours or longer, desirably 3 to 10 hours. A preferable sintering temperature is higher than 1300 ° C. and 1500 ° C. or lower, more preferably 1320 ° C. or higher and 1480 ° C. or lower, and further preferably 1350 ° C. or higher and 1450 ° C. or lower. 10-500 degreeC / h is preferable and, as for the temperature increase rate until it makes it reach the said sintering temperature (for example, 1300 degreeC) from room temperature, More preferably, it is 50-300 degreeC / h.

  Since the sintering process of the present invention can be performed at normal pressure and / or without applying a load, it is simpler and easier without using pressure sintering by a hot press as employed in Patent Document 1. Sintering can be performed by a method suitable for mass production. In particular, when sintering is performed by hot pressing, a graphite mold is generally used. However, at a firing temperature of 1300 ° C. or higher, volatilization of ZnO becomes intense due to the reducing atmosphere formed by graphite. Densification is hindered. In this regard, the sintering process of the present invention can be performed at normal pressure and / or without applying a load, avoiding hot pressing having such disadvantages. For this reason, high density and low resistance of the target can be efficiently realized. In addition, pressure sintering by hot pressing must be performed by batch processing that uses a hot pressing mold to sinter one by one, resulting in poor productivity and large restrictions on the shape and size depending on the hot pressing mold. Typically, the shape of the sintered body tends to be limited to a disk shape. On the other hand, according to the sintering process performed at normal pressure and / or without applying a load, since a sintered body can be obtained in a plate shape having a desired shape and size, it is excellent in mass productivity. For example, it is suitable for manufacturing a large-sized plate-like sintered body and processing it into a rectangular plate widely used as a sputtering target, and it is also possible to manufacture a sputtering target having a special shape such as a cylindrical shape. .

  According to a preferred embodiment of the present invention, prior to the sintering step, by performing a pre-baking step of holding the molded body at a temperature of 900 to 1200 ° C. for 2 hours or more, desirably 3 to 10 hours, the subsequent 1300 ° C. It is good also as a structure which performs a two-step baking process with the above sintering process. Thereby, the density of the target can be further increased and the resistivity can be further reduced.

  The sintering step and the preliminary firing step are preferably performed in an atmosphere of an inert gas such as nitrogen or argon in order to reduce the resistivity.

  The present invention is more specifically described by the following examples.

Example 1
Θ-alumina powder (specific surface area 72.9 m ² / g, manufactured by Sumitomo Chemical Co., Ltd.) was prepared as an Al source. An SEM photograph of the θ-alumina powder is shown in FIG. This θ-alumina powder and ZnO powder (manufactured by High-Purity Chemical Laboratory, purity 5N, specific surface area 3.9 m ² / g) were mixed so that ZnO was 98 parts by weight and θ-alumina was 2 parts by weight. Weighed. These powders were ball milled for 3 hours to obtain a slurry. This ball mill treatment was performed using ZrO ₂ balls having a diameter of 2 mm using ethanol as a solvent. The obtained slurry was dried with an evaporator and passed through a # 100 mesh to obtain a mixed powder of ZnO and θ-alumina. This mixed powder was press-molded using a mold and further subjected to isostatic pressing at a pressure of ² t / cm ² to obtain a molded body. The molded body was placed in a firing furnace, heated in a N ₂ atmosphere from room temperature to 1300 ° C. at a rate of 200 ° C./h, held at 1300 ° C. for 5 hours, and then cooled in the furnace. A sintered body was obtained. A sample having a size of 3 mm × 4 mm × 40 mm was cut out from the obtained sintered body, and the bulk density was measured by Archimedes method. The resistivity of the sintered body was also measured by a four-terminal method using an Ag wire as an electrode.

Example 2
In the same manner as in Example 1 except that boehmite (AlOOH) (specific surface area 137.4 m ² / g, manufactured by Sasol) was used as an alumina raw material in an amount of 2 parts by weight (2.34 parts by weight of boehmite) in terms of alumina. Production and evaluation of the ligature were performed. An SEM photograph of boehmite is shown in FIG. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 3
A sintered body was prepared and evaluated in the same manner as in Example 1 except that γ-alumina (specific surface area 148.1 m ² / g, manufactured by Sumitomo Chemical Co., Ltd.) was used as the alumina raw material. FIG. 3 shows an SEM photograph of γ-alumina, and Table 1 shows the evaluation results. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 4
A sintered body was produced and evaluated in the same manner as in Example 1 except that the temperature was raised to 1400 ° C. during firing and the temperature was maintained at 1400 ° C. for 5 hours. The evaluation results are shown in Table 1. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 5
Boehmite (AlOOH) (specific surface area 137.4 m ² / g, manufactured by Sasol) was used as an alumina raw material by 2 parts by weight (2.34 parts by weight boehmite) in terms of alumina, and the temperature was raised to 1400 ° C. during firing. A sintered body was prepared and evaluated in the same manner as in Example 1 except that the temperature was maintained at 1400 ° C. for 5 hours. The evaluation results are shown in Table 1. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 6
Same as Example 1 except that γ-alumina (specific surface area 148.1 m ² / g, manufactured by Sumitomo Chemical Co., Ltd.) was used as the alumina raw material, and the temperature was raised to 1400 ° C. during firing and held at 1400 ° C. for 5 hours. Thus, the sintered body was produced and evaluated. The evaluation results are shown in Table 1. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 7
Preparation and sintering of the sintered body were performed in the same manner as in Example 1 except that preheating was performed by holding at 900 ° C. for 5 hours at the time of temperature rise, and then heated to 1400 ° C. and fired at 1400 ° C. for 5 hours at normal pressure. Evaluation was performed. The evaluation results are shown in Table 1. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 8
Boehmite (AlOOH) (specific surface area 137.4 m ² / g, manufactured by Sasol) was used as an alumina raw material in an amount in terms of alumina of 2 parts by weight (2.34 parts by weight of boehmite) and at 900 ° C. for 5 hours when the temperature was raised. The sintered body was produced and evaluated in the same manner as in Example 1 except that the preheating was carried out while maintaining the temperature, and the temperature was raised to 1400 ° C. and firing was performed at 1400 ° C. for 5 hours under normal pressure. The evaluation results are shown in Table 1. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 9
Γ-alumina (specific surface area 148.1 m ² / g, manufactured by Sumitomo Chemical Co., Ltd.) was used as an alumina raw material, and preheating was performed while maintaining the temperature at 900 ° C. for 5 hours during the temperature increase, and then the temperature was increased to 1400 ° C. Then, a sintered body was prepared and evaluated in the same manner as in Example 1 except that firing was performed at 1400 ° C. for 5 hours under normal pressure. The evaluation results are shown in Table 1. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 10
Preparation of sintered body in the same manner as in Example 1 except that preliminary firing was performed by holding at 1100 ° C. for 5 hours at the time of raising the temperature, then raising the temperature to 1400 ° C. and firing at normal pressure at 1400 ° C. for 5 hours. And evaluated. The evaluation results are shown in Table 1. The resistivity was calculated as a relative value to the value obtained in Example 1.

Example 11 (Comparison)
A sintered body was prepared and evaluated in the same manner as in Example 1 except that α-alumina (specific surface area 12.6 m ² / g, manufactured by Daimei Chemical Industries) was used as the alumina raw material. FIG. 4 shows the SEM photograph of α-alumina, and Table 1 shows the evaluation results. The resistivity was calculated as a relative value to the value obtained in Example 1.

  As shown in Table 1, in Examples 1 to 10 using alumina or boehmite having a large specific surface area as a dopant material, alumina having a small specific surface area was used when sintering was performed at a high temperature of 1300 ° C. or higher. Compared to Example 11, a high density and low resistivity target was obtained.

Claims (9)

A step of adding a dopant material containing alumina and / or boehmite having a specific surface area of 40 to 200 m ² / g to zinc oxide powder to obtain a mixed powder;
Molding the mixed powder to obtain a molded body;
Ri Na comprise the steps of obtaining a zinc oxide-based sputtering target by sintering the green body at 1300 ° C. or higher,
The method for producing a zinc oxide-based sputtering target , wherein the sintering step includes holding the compact at a temperature of 1300 ° C. or more for 2 hours or more .   The method according to claim 1, wherein the alumina and / or boehmite is at least one selected from the group consisting of θ-alumina, γ-alumina and boehmite.   The method according to claim 1, wherein the molding step includes press molding.   The method according to claim 1 or 2, wherein the molding step is performed by press molding and subsequent isostatic pressing.   The method according to claim 1, wherein the sintering step is performed at normal pressure and / or without applying a load. The method according to any one of claims 1 to 5 , further comprising a pre-baking step of holding the compact at a temperature of 900 to 1200 ° C for 2 hours or more before the sintering step. The method according to any one of claims 1 to 6 , wherein the sintering step, or the preliminary firing and the sintering step are performed in an inert gas atmosphere. The amount of the alumina and / or boehmite, 1 to 3% by weight relative to the total amount of the mixed powder, method according to any one of claims 1-7. The method according to any one of claims 1 to 8 , wherein the alumina and / or boehmite mainly comprises fine particles having a particle size of 100 nm or less.