JP5392633B2 - Target for ZnO-based transparent conductive film and method for producing the same - Google Patents

Description

  The present invention relates to a target for a ZnO-based transparent conductive film to which both boron (B) and vanadium (V) used for manufacturing liquid crystal displays and thin film solar cells are added, and a method for manufacturing the same.

In liquid crystal displays, thin film solar cells, and the like, electrodes that are conductive and transparent to light (transparent electrodes) are used. Examples of materials having such properties include In ₂ O ₃ —SnO ₂ (hereinafter referred to as ITO), ZnO—B ₂ O ₃ (hereinafter referred to as BZO), ZnO—Al ₂ O ₃ (hereinafter referred to as AZO), and ZnO—Ga. An oxide material such as ₂ O ₃ (hereinafter GZO) is known. Such a material is formed as a thin film on a liquid crystal display or thin film solar cell by sputtering, and then patterned as an electrode to become a transparent electrode.

  In the sputtering method, in a sputtering apparatus, a substrate on which a thin film is formed and a sputtering target (hereinafter, target) are arranged to face each other. A gas discharge is generated between them, ions generated by the gas discharge collide with the surface of the target, and atoms (particles) released by the impact are attached to the opposing substrate to form a thin film. This target is formed of a material that becomes a transparent electrode, and the characteristics of the transparent electrode are reflected in the characteristics of the target used.

In general, the target is very expensive, and the price accounts for a large proportion of the manufacturing cost of the liquid crystal display and solar cell. For this reason, in order to reduce the cost of liquid crystal displays and solar cells, the target is also required to be inexpensive. Among them, the BZO target is manufactured using ZnO powder and B ₂ O ₃ powder, which are inexpensive raw materials, and is promising for cost reduction. Furthermore, BZO is promising as a transparent electrode for solar cells because it has a high transmittance of 1000 nm or more compared to ITO and AZO used as transparent electrodes, and sunlight can be used effectively. However, in order to obtain a BZO target by sintering ZnO powder and _B 2 _{O 3 powder,} fused by _B 2 _{O 3} between B from 2 _{O 3} is around about 600 ° C. for the liquid phase begins to generate, It has been pointed out that it is difficult to obtain a dense sintered body due to problems such as coarsening and segregation in the sintered body, or wettability and problems of evaporation of B ₂ O ₃ .

In order to solve this problem, a raw material comprising a composite powder obtained by calcining ZnO powder and B ₂ O ₃ powder is used, or a composite obtained by calcining a powder of hydroxide by a coprecipitation method. It is disclosed that a raw material made of powder is used (Patent Document 1, Patent Document 2, and Patent Document 3).
Thus, the use of the composite powder formed in advance is effective in preventing segregation and obtaining a dense sintered body because the coarse B ₂ O ₃ phase does not exist.

In addition, it is disclosed that Co and V addition are effective in increasing the chemical resistance of ZnO (Patent Document 4).
According to Patent Document 4, it is effective to add Co and V to a ZnO-based conductive film to which the above-mentioned group III element to which boron belongs, which is used as a donor impurity, is added. Sputtering is used to form such a conductive film. The method is applied, and there is also a disclosure of a sintered body for that purpose.

Japanese Patent Laid-Open No. 11-158607 Japanese Patent Laid-Open No. 11-171539 JP-A-11-302835 JP 2002-75062 A

Although V disclosed in Patent Document 4 is advantageous in terms of improving chemical resistance, when V ₂ O ₅ specifically described in Patent Document 4 is used as a vanadium source, V ₂ O ₅ Careful handling of toxicity is required.
V ₂ O ₃ is known as a V oxide having lower toxicity than V ₂ O ₅ , but the melting point of V ₂ O ₅ is as low as 690 ° C., whereas V ₂ O _{3 has} a low melting point. The melting point was as high as 1970 ° C., and the behavior for obtaining a ZnO-based sintered body containing boron was unknown.

In addition, for the addition of boron, a method of forming a composite oxide as in Patent Documents 1 to 3 is effective. However, even in the manufacturing technology using such a composite oxide, it has been completely unknown how the valence of V of the raw material oxide when adding V has an effect on the sinterability.
The objective of this invention is providing the target for ZnO type transparent conductive films which added both the boron (B) and vanadium (V) which have a high sintered density, and its manufacturing method.

The present inventor has found that V ₂ O ₃ contributes to the improvement of the sintering density in obtaining a sintered body containing boron, and has reached the present invention.
That is, according to the present invention, the amount of boron is 0.5 to 10 mass% in terms of an oxide with B ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100, and the amount of vanadium is V ₂ O ₃ / (ZnO + B). in _{2 O 3 + V 2 O 3} ) × 100 and the oxide equivalent was 0.05~5mass%, the density of ZnO-based transparent conductive film for the target is an oxide sintered body of 90% or more in relative density is there.
In the present invention, aluminum and / or gallium can be added in an amount of 2 mass% or less in terms of trivalent oxide.

The manufacturing method of the present invention contains boron and vanadium, boron _amount, B ₂ O 3 _{/ 0.5~10mass%} in _{(ZnO + B 2 O 3 +} V 2 O 3) × 100 and the oxide equivalent, Manufacture of a target for a ZnO-based transparent electrode comprising an oxide sintered body having a vanadium amount of 0.05 to 5 mass% in terms of an oxide of V ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100 This is a method for producing a target for a ZnO-based transparent conductive film using H ₃ BO ₃ powder as a boron source and V ₂ O ₃ powder as a vanadium source.
The sintering temperature in the production method of the present invention is preferably 700 to 1050 ° C., and the sintering atmosphere is preferably a non-reducing atmosphere.
In the method of the present invention, the H ₃ BO ₃ powder, ZnO powder or further mixing a V ₂ O ₃ powder, it is preferable to sinter the calcined powder obtained by calcining a sintering raw material .

Further, when the calcined powder is used in the present invention, the composition of the calcined powder is 0.8 to 45 mass% in terms of oxide in which the composition of the calcined powder is B ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100. It is preferable to obtain a sintered body having a relative density of 90% or more by mixing and sintering either or both of ZnO powder and V ₂ O ₃ to the calcined powder.
Moreover, it is preferable that a calcination temperature shall be 100-500 degreeC.

  The present invention is a ZnO-based transparent conductive film target to which both boron (B) and vanadium (V) having a high sintered density are added, and is suitable for the production of liquid crystal displays, thin film solar cells, etc. with less abnormal discharge. is there. Further, the production method of the present invention is an important technique for obtaining the above-mentioned target because it can be produced safely and with high accuracy.

It is a figure which shows an example of the microstructure of the target of this invention, and corresponding specific atom distribution. It is a figure which shows an example of the microstructure of the target of a comparative example, and corresponding specific atom distribution.

As described above, an important feature of the present invention is that V ₂ O ₃ has been found to contribute to the improvement of the sintering density in obtaining a sintered body containing boron, and boron and vanadium having a high sintering density have been found. That is to realize a ZnO-based transparent conductive film target to which both are added.
In the present invention, the amount of boron is set to 0.5 to 10 mass% in terms of an oxide of B ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100. The conductive film formed by boron addition This is because it is effective in ensuring low resistance and transparency. Preferably, it is 0.5-5 mass%.
Further, in the present invention, the vanadium _amount, was _{V 2 O 3 / (ZnO +} B 2 O 3 + V 2 O 3) × 100 and the 0.05 mass% or more in terms of oxide, in less than 0.05 mass%, This is because a clear effect of improving the sinterability cannot be obtained, and it is difficult to uniformly disperse the target during production. The reason why it is set to 5 mass% or less is to maintain the effect of boron addition, which is inexpensive and has a high transmittance at a specific wavelength. Preferably, it is 0.05-2 mass%.

  In the present invention, an oxide that imparts conductivity other than boron and vanadium is not necessarily required in order to make use of the characteristics of boron, but it can be added. Typically, an oxide of aluminum (Al) or gallium (Ga) can be added. These additions are preferably 2 mass% or less in terms of trivalent oxide.

The relative density of the target of the present invention was 90% or more. If it is less than 90%, it can be easily reached even by ordinary sintering, and therefore there is little meaning of improving the sinterability by adding V ₂ O ₃ . Preferably, it is 95% or more. More preferably, it is 98% or more.
The relative density in the present invention, the relative density to the density of the target tissue, ZnO, assuming each phase of _{B 2 O 3, V 2 O} 3 is present in each independently, is calculated It is.

Next, the production method of the present invention will be described in detail.
In the production method of the present invention, in order to obtain a target having the above-described composition, there is one of important features in using H ₃ BO ₃ powder as a boron source and V ₂ O ₃ powder as a vanadium source.
B ₂ O ₃ powder, which is usually used as a boron source, has been confirmed to have a problem that it has high hygroscopicity and easily causes a weighing error. On the other hand, the H ₃ BO ₃ powder used in the present invention is a hydrate, has no concern of moisture absorption, is less prone to weighing errors, and is effective in increasing the accuracy of component adjustment.
Further, V ₂ O ₅ usually used as a vanadium source is toxic as described above and has a problem in handling. On the other hand, V ₂ O ₃ used in the present invention does not have such a problem. What is important is that it has been found that V ₂ O ₃ contributes to enhancing the sinterability despite having a high melting point of 1970 ° C.

According to the study of the present inventor, the structure of the Zn—B—O phase existing in the target structure is a granular structure when V ₂ O _{3 is} not added, whereas a columnar structure is obtained by adding V ₂ O _3. The phenomenon of becoming is confirmed. From this fact, it is presumed that the added V ₂ O ₃ powder has a great influence on the target structure and is a factor for improving the sinterability.
By this method, the relative density can be increased to 90%, preferably 95% or more, more preferably 98% or more.

The sintering temperature in the production method of the present invention is preferably 700 to 1050 ° C., and the sintering atmosphere is preferably a non-reducing atmosphere. If the sintering temperature is less than 700 ° C., the sintering time is too long. If the sintering temperature is 1050 ° C. or more, the decomposition of the constituent oxide proceeds and a predetermined sintering density cannot be obtained. Because there is.
Further, by selecting a non-reducing atmosphere as the sintering atmosphere, there is an advantage that decomposition of the constituent oxide can be easily suppressed. As this non-reducing atmosphere, air, nitrogen, inert gas, or the like can be used.

In the production method of the present invention, the use of H ₃ BO ₃ powder is effective for controlling the composition as described above. However, if the sintering raw material is used as it is, it is decomposed into boron oxide and water by heating. As in the case of using the raw material for binding, large segregation may occur in the sintered body or a dense sintered body may not be obtained.
For this reason, when a calcined powder obtained by mixing ZnO powder and H ₃ BO ₃ powder and calcining is used as a sintering raw material, a complex oxide is formed. It becomes possible to obtain a ligation. Further, the calcining step can remove moisture unnecessary for the sintered body in advance, and is effective in preventing deformation of the sintered body and formation of defects due to the presence of moisture. At this time, V ₂ O ₃ powder may be mixed at the same time to obtain a calcined powder.

In the production method of the present invention, sintering may be performed using only the calcined powder as a raw material, but other oxide powder may be mixed and sintered in addition to the calcined powder. Specifically, the composition of the calcined powder is adjusted to 0.5-45 mass% in terms of oxide, which is B ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100, It is desirable to mix and sinter either ZnO powder or V ₂ O ₃ or both.

The reason why the B ₂ O ₃ ratio is 0.5% or more is that if it is less than 0.5%, it is difficult to obtain the characteristics as an electrode, and it is necessary to add another boron source in addition to the calcined powder. This is because it occurs.
On the other hand, the B ₂ O ₃ ratio is set to 45% or less because when it exceeds 45%, the amount existing as a B ₂ O ₃ phase increases in addition to the composite oxide. This is because dispersibility may deteriorate. The actual composition of the calcined powder, adjusting the amount and ZnO amount of ZnO powder, or _V 2 _{O 3} amount of _V 2 _{O 3} powder in the case _{of H} 3 BO ₃ powder used becomes _B 2 _{O 3} Can do.

In the calcining step, the calcining temperature is preferably 100 ° C. or more and 500 ° C. or less. This is because when the temperature is lower than 100 ° C., decomposition and removal of water from H ₃ BO ₃ is difficult to proceed.
On the other hand, when the temperature is higher than 500 ° C., the calcined powder grows greatly, and a special pulverization treatment or the like is required as a sintering raw material.

Examples of the present invention will be described below. However, the present invention is not limited to the examples described below.
The manufacturing process applied in this example is as follows.
(Process A1)
ZnO powder having a specific surface area of 4.5 m ² / g and H ₃ BO ₃ powder were weighed so as to have a predetermined target composition shown in Table 1, and then mixed in a ball mill to prepare a mixed powder.
The obtained mixed powder was calcined at a predetermined temperature to obtain a calcined powder. The obtained calcined powder was weighed with a V ₂ O ₃ powder so as to have a predetermined target composition, and then mixed with a ball mill to prepare a mixed powder. After adding 0.5 mass% of polyvinyl alcohol as a binder to the obtained mixed powder and mixing while grinding, granulated granulated powder was prepared.
In the case of adding other oxide powder was added in the same manner as V ₂ O _3.

(Process A2)
ZnO powder having a specific surface area of 4.5 m ² / g, H ₃ BO ₃ powder, and V ₂ O ₃ powder were weighed so as to have a predetermined target composition, and then mixed by a ball mill to prepare a mixed powder. The obtained mixed powder was calcined at a predetermined temperature to obtain a calcined powder. After adding 0.5 mass% of polyvinyl alcohol as a binder to the obtained calcined powder and mixing while grinding, granulated granulated powder was prepared.
(Process A3)
As a process of the comparative example, ZnO powder having a specific surface area of 4.5 m ² / g and H ₃ BO ₃ powder were weighed so as to have a predetermined target composition, and then mixed by a ball mill to prepare a mixed powder.
The obtained mixed powder was calcined at a predetermined temperature to obtain a calcined powder. After adding 0.5 mass% of polyvinyl alcohol as a binder to the obtained calcined powder and mixing while grinding, granulated granulated powder was prepared.

(Process B)
Next, the granulated powder obtained in any one of steps A1 to A3 is molded with a cold isostatic press at a pressure of 3 ton / cm ² to obtain a disk-shaped molded body having a diameter of 120 mm and a thickness of 8 mm. It was. The obtained molded body was sintered at a predetermined temperature and atmosphere shown in Table 1 to produce a sintered body. The obtained sintered body was processed into a disk shape having a diameter of 100 mm and a thickness of 5 mm to produce a sputtering target.

(Target evaluation)
The density of the sintered body obtained in the manufacturing process was measured by an underwater substitution method, and the value obtained by dividing by the theoretical density obtained on the assumption that the components constituting the sintered body existed as a predetermined oxide was taken as the relative density. . In the composition analysis of the sintered body, Zn amount, B amount, V amount, Al amount, and Ga amount are analyzed by high frequency inductively coupled plasma emission spectroscopy (ICP-AES), and ZnO, B ₂ O ₃ , V ₂ are analyzed. O _3, was determined by _Al 2 _O 3, again in terms of the oxides of _Ga 2 _{O 3,} but was consistent with the aim composition. These results are shown in Table 1.
The obtained sintered body was observed with a scanning electron microscope, and the element distribution in the structure was mapped with EPMA. As a typical example, FIG. 1 shows the microstructure of the target of Example 2 and FIG. 2 shows the corresponding specific atom distribution of Comparative Example 2.

The four observation images shown in FIG. 1 and FIG. 2 respectively show the structure of the scanning microscope in the upper left, the B atom distribution in the corresponding visual field in the upper right, the V atom distribution in the corresponding visual field in the lower left, and the Zn in the corresponding visual field in the lower right. The atomic distribution is shown. In addition, the atomic distribution indicates that the concentration is high in the order of black-white-brown.
In Examples and Comparative Examples, a Zn ₃ B ₂ O ₆ compound was detected by X-ray diffraction analysis in the boron enriched portion, and a Zn ₃ (VO ₄ ) ₂ compound was detected in the vanadium enriched portion. .

(Film formation evaluation)
Using the manufactured target, a film having a thickness of 200 nm was formed by DC magnetron sputtering. The sputtering conditions were fixed at an input power of 200 W and an Ar gas pressure of 0.7 Pa. Then, the number of abnormal discharges generated per 10 minutes after the start of the experiment, the volume resistivity of the film at a substrate temperature of 200 ° C., and the transmittance in the 1200 nm wavelength region were measured. Further, the film at a substrate temperature of 200 ° C. is exposed to an environment of a temperature of 60 ° C. and a humidity of 90%, the volume resistivity after 1000 hours of exposure is measured, and the volume resistivity after exposure to the volume resistivity before exposure. Was evaluated for changes. The results are shown in Table 2.

In Table 1, for example, when Example 3 and Comparative Example 1 are compared, the relative density increases remarkably even under the same sintering conditions by adding V ₂ O ₃ to the same amount of B ₂ O ₃ . You can see that Further, when Example 3 and Comparative Example 2 are compared, it can be seen that when V ₂ O ₃ is not added, an approximate sintered density is finally obtained at a sintering temperature as high as 1000 ° C. These results indicate that the addition of V ₂ O ₃ effectively acts to increase the sintered density in obtaining a ZnO-based sintered body containing boron.
In Table 2, the addition of V ₂ O _3, notice that the change of the volume resistivity can be suppressed, the addition of V ₂ O ₃ it can be seen that to improve the environmental resistance. Further, the transmittance of 1200 nm is not greatly deteriorated even by the addition of the predetermined V ₂ O ₃ , so that it is effective in that the characteristics of the ZnO-based sintered body containing boron can be maintained.

Claims (8)

The amount of boron is 0.5 to 10 mass% in terms of an oxide with B ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100, and the amount of vanadium is V ₂ O ₃ / (ZnO + B ₂ O ₃ + V _2. A target for a ZnO-based transparent conductive film, characterized in that it is an oxide sintered body having an O ₃ ) × 100 oxide conversion of 0.05 to 5 mass% and a relative density of 90% or more.   2. The ZnO-based transparent conductive film target according to claim 1, wherein aluminum and / or gallium is converted into a trivalent oxide and each contains 2 mass% or less. It contains boron and vanadium, and the amount of boron is 0.5 to 10% by mass in terms of oxide with B ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100, and the amount of vanadium is V ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100 A method for producing a ZnO-based transparent electrode target comprising an oxide sintered body having an oxide conversion of 0.05 to 5 mass% in terms of an oxide, wherein H is used as a boron source. ₃ BO ₃ powder, ZnO-based transparent conductive film target manufacturing method which comprises using a _V 2 _{O 3} powder as a vanadium source.   The method for producing a target for a ZnO-based transparent conductive film according to claim 3, wherein the ZnO-based transparent electrode target contains 2 mass% or less of aluminum and / or gallium as a trivalent oxide. .   The method for producing a target for a ZnO-based transparent conductive film according to claim 3 or 4, wherein the sintering temperature is 700 to 1050 ° C, and the sintering atmosphere is a non-reducing atmosphere. 6. The calcined powder obtained by mixing H ₃ BO ₃ powder with ZnO powder or further V ₂ O ₃ powder and calcining is sintered as a sintering raw material. 6. A method for producing a target for a ZnO-based transparent conductive film according to claim 1. The calcined powder has a composition of 0.5 to 45 mass% in terms of an oxide in which the composition of the calcined powder is B ₂ O ₃ / (ZnO + B ₂ O ₃ + V ₂ O ₃ ) × 100, and the calcined powder has ZnO powder or V ₂ O _3. A method for producing a target for a ZnO-based transparent conductive film according to claim 6, wherein either or both of the above are mixed and sintered to obtain a sintered body having a relative density of 90% or more.   The method for producing a target for a ZnO-based transparent conductive film according to claim 6 or 7, wherein the calcining temperature is 100 to 500 ° C.

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