JP6225530B2 - Sputtering target and manufacturing method thereof - Google Patents

Description

  The present invention relates to a sputtering target capable of stably forming a uniform and low-resistance ZnO-based transparent conductive film by direct current (DC) sputtering and a method for manufacturing the same.

An ITO film, which is a transparent conductive film, is known as an electrode material for solar cells and liquid crystal displays. As an alternative to the ITO transparent electrode film, for example, a ZnO—Al ₂ O ₃ (AZO) film or a ZnO—Ga ₂ O ₃ (GZO) film is employed. As a method of forming this AZO / GZO film, film formation by sputtering is known, and sputtering film formation is performed using a DC power source.

An AZO sputtering target / GZO sputtering target used for forming the AZO / GZO film has been developed. The conductivity of this AZO · GZO film is not only due to the generation of carriers due to the addition of Al ₂ O ₃ · Ga ₂ O ₃ to ZnO, but also the main component ZnO is oxygen deficient (state in which O is released from ZnO). It is known that it is an oxide, that is, due to oxygen vacancies in ZnO.

In the production of the GZO sputtering target disclosed in Patent Document 1, a mixture of zinc oxide (ZnO) powder and gallium oxide (Ga ₂ O ₃ ) powder mixed at a predetermined ratio is used with a cold molding machine. Molding is performed to produce a compact, and this compact is subjected to atmospheric pressure sintering in an air atmosphere to obtain a sintered compact. The sintered body after the sintering is subjected to a reduction treatment to promote oxygen deficiency of ZnO and further reduce the volume resistivity as a sputtering target.

Patent No. 4026194 specification

  As described above, in the GZO sputtering target proposed in Patent Document 1, a mixture in which gallium oxide powder is added to zinc oxide powder is molded and sintered under atmospheric pressure, so in ZnO In this way, Ga of gallium oxide can be dissolved, and a densified sintered body can be obtained. Further, after the sintering, the sintered body is subjected to a reduction treatment in which a non-oxidizing gas is introduced, so that an increase in oxygen vacancies in ZnO is promoted.

  However, after obtaining a sintered body that has already been sintered and has a high density, it is only possible to reduce the surface portion of the sintered body by simply exposing it to a reducing atmosphere and reducing the resistivity of the target surface portion. There is a possibility that the reduction reaction does not proceed to the inside of the sintered body and the reduction is not promoted inside the target.

  Using such a sintered body, for example, when an attempt is made to produce a zinc oxide-based sputtering target exceeding the size of 100 mm in diameter and 10 mm in thickness, the target surface portion is sufficiently reduced, but proceeds to the inside of the target. As a result, a phase with an insufficient reduction effect remains. Therefore, variation in resistivity occurs in the thickness direction of the sputtering target. When sputtering is performed with this sputtering target, the surface portion has a low resistivity, and DC sputtering is possible. However, when the inside of the target is dug as the sputtering proceeds, there is a problem that a portion having high resistivity is exposed on the surface, so that abnormal discharge occurs frequently and sputtering cannot be performed stably.

  Therefore, the present invention promotes the increase in oxygen vacancies in ZnO uniformly and sufficiently over the thickness direction (erosion depth direction) of the zinc oxide-based sputtering target and promotes the sintering reaction to increase the thickness. An object of the present invention is to provide a zinc oxide-based sputtering target containing ZnO as a main component, which has a lower target resistivity all over the direction and can always perform stable DC sputtering, and a method for manufacturing the same.

  In the zinc oxide-based sputtering target proposed in Patent Document 1 above, attention is paid to the fact that the resistivity of the target is low at the target surface portion and increases as it goes into the target. However, as the change is made uniform, the powder compact formed from the raw material powder is degreased by heating in an oxidizing atmosphere, and the degreased compact compact is made non-oxidizing. When atmospheric pressure sintering is performed in the atmosphere, reduction to the inside of the target is promoted, and oxygen vacancies are generated to the inside, so that the target resistivity is reduced in the entire area in the target thickness direction, and at the time of sintering As a result of accelerating the movement of oxygen atoms, the density of the sintered body is improved, and a zinc oxide-based sputtering that enables stable DC sputtering at all times. It has been found that grayed target is obtained.

Therefore, a dispersant and a binder are added to a mixture obtained by mixing commercially available zinc oxide powder (ZnO powder) and aluminum oxide powder (Al ₂ O ₃ powder), and pressure is applied to the resulting slurry to form a compact. A molded body was produced. This compacted body is heated in a heating furnace in the air atmosphere, degreased, and then nitrogen (N ₂ ) gas is introduced into the heating furnace to maintain high temperature (1350 ° C.) heating for 5 hours for sintering. Thus, a zinc oxide-based (AZO) sintered body was obtained. When this AZO sintered body was machined into a predetermined shape to produce an AZO sputtering target, it was confirmed that the target resistivity could be further reduced in the entire region in the target thickness direction. It was confirmed that stable DC sputtering was always possible in the formation of an AZO film using this AZO sputtering target. The same applies to the case of a zinc oxide-based sintered body using gallium oxide (Ga ₂ O ₃ ) powder or indium oxide (In ₂ O ₃ ) powder instead of aluminum oxide (Al ₂ O ₃ ) powder. .

  This is because the compacted body was sintered in a nitrogen gas atmosphere, and the target resistivity was that sufficient reduction could be achieved throughout the thickness direction up to the inside of the zinc oxide-based sintered body. The knowledge that it contributed to the further fall of was obtained.

Therefore, the present invention has been obtained from the above findings, and the following configuration has been adopted in order to solve the above problems.
(1) A sputtering target for DC sputtering according to the present invention is a zinc oxide-based sintered body containing zinc oxide as a main component and containing one or more metal oxides selected from A and In as a component composition, The zinc-based sintered body has a resistivity of 0.0001 to 0.005 Ω · cm, and a maximum difference in resistivity in the target thickness direction is 0.00011 to 0.003 Ω · cm. And
(2) The zinc oxide-based sintered body of the sputtering target of (1) is characterized in that the maximum difference in resistivity within the sputtering plane is 0.00013 to 0.003 Ω · cm .
(3) The method for producing a sputtering target for DC sputtering according to the present invention comprises a degreasing treatment in an air atmosphere while heating a compacted body of zinc oxide powder and one or more metal oxide powders selected from A and In. Degreasing step and heating temperature: when the temperature is 500 to 700 ° C., the oxidizing atmosphere is switched to the non-oxidizing atmosphere, and the degreased green compact is subjected to normal pressure sintering at 1200 to 1500 ° C. in a non-oxidizing atmosphere. And a sintering step of reducing zinc oxide.

Zinc oxide-based sputtering target according to the present invention, the zinc oxide as a main component, A, composed of zinc oxide-based sintered body containing the chemical composition of at least one metal oxide selected from I n. This zinc oxide-based sintered body has a bulk resistivity as low as 0.0001 to 0.005 Ω · cm by performing a reduction treatment uniformly over the entire region in the thickness direction. Furthermore, when the maximum difference in resistivity in the target thickness direction is 0.00011 to 0.003 Ω · cm 2 and the maximum difference in resistivity in the sputtering surface is 0.00013 to 0.003 Ω · cm , the resistivity The DC sputtering can be stabilized by reducing the variation of.

Moreover, the manufacturing method of this invention manufactures the said zinc oxide type | system | group sputtering target, Comprising: The compacting body of a zinc oxide powder and 1 or more types of metal oxide powder chosen from A , In is air | atmosphere. A degreasing step of degreasing treatment in an atmosphere, and a sintering step of reducing the zinc oxide by subjecting the degreased green compact to normal pressure sintering in a non-oxidizing atmosphere.

The green compact includes a zinc oxide (ZnO) powder, aluminum oxide _(Al 2 _{O 3)} powder powder及 beauty indium oxide _(In 2 _{O 3)} and any one of powders, furthermore, pure water, a dispersant and A polyvinyl alcohol-based binder is filled in a ball mill, and the slurry obtained by the ball mill mixing is dried and granulated with a spray dryer, and the obtained granulation is used to apply a cold isostatic pressure (CIP) machine. It is pressure-molded.

  The green compact obtained here is inserted into a heating furnace, heating is started, and the process moves to the degreasing step. In this degreasing step, the heating furnace is heated to 500 to 700 ° C. in an atmospheric oxidizing atmosphere, for example, an air atmosphere. During the temperature increase, the dispersant and binder in the green compact are completely burned and burned off, and the green compact is sufficiently degreased.

Next, the temperature of the heating furnace is further increased while leaving the degreased compacted body in the heating furnace, and the process proceeds to the sintering step. When shifting to this sintering process, the atmosphere in the heating furnace is switched from the oxidizing atmosphere (atmospheric atmosphere) to the introduction of non-oxidizing (reducing) gas (gas injection timing) to make a non-oxidizing atmosphere. . As this non-oxidizing atmosphere, nitrogen (N ₂ ) gas, argon (Ar) gas, carbon dioxide (CO ₂ ) gas, helium (He) gas, or the like can be introduced, or a vacuum atmosphere can be adopted.

  In this sintering step, the temperature is further increased to 1200 to 1500 ° C., for example, 1350 ° C., and when this temperature is reached, the temperature is maintained for 3 to 10 hours thereafter. For example, hold for 5 hours. After elapse of this holding time, the heating furnace is gradually cooled to 500 to 700 ° C. to complete the sintering process. And it cools naturally, it takes out from a heating furnace, the sintered compact is machined, a backing plate is adhere | attached, and a zinc oxide type | system | group sputtering target is produced.

  In the sintering step in the production method of the present invention, it is important that the compacted body that has been sufficiently degreased is sintered by being kept at a high temperature for a predetermined time in a non-oxidizing atmosphere at normal pressure. is there. In this sintering process, zinc oxide is sufficiently reduced to the inside of the green compact, and the amount of oxygen vacancies increases uniformly throughout the sintered body. Therefore, the sintering reaction is promoted, the density of the sintered body is improved, the volume resistivity of the sintered body is further reduced, and the entire surface of the sputtering surface is spread over the entire thickness direction. Thus, variation in resistivity can be reduced.

  In the above description, the case where the degreasing step and the sintering step are performed using the same heating furnace has been described. However, even if the degreasing step and the sintering step are performed using different heating furnaces, the manufacturing method of the present invention is used. Can be implemented.

  As described above, according to the present invention, the sintered body of the zinc oxide-based sputtering target is obtained by subjecting the compacted body after degreasing to normal pressure sintering in a non-oxidizing atmosphere, and the entire area inside the target. In this case, the zinc oxide-based sputtering target has a resistivity in the entire region in the target thickness direction (erosion depth direction) because the oxygen deficiency is increased and the sintering reaction is promoted. As a result, the variation in resistivity in the target thickness direction and in the sputtering surface became small.

According to the production method of the present invention, a degreased treated zinc oxide powder and A l, the green compact with one or more metal oxides powder selected from I n an oxidizing atmosphere, degreasing The sintered compact is subjected to atmospheric pressure sintering in a non-oxidizing atmosphere to reduce zinc oxide. In the degreasing process, organic substances in the compact are burned off. In the subsequent sintering process, since the oxidizing atmosphere is switched to the non-oxidizing atmosphere, in this sintering process, the reduction proceeds sufficiently to the inside of the sintered body, the amount of oxygen deficiency increases uniformly, Since the generation of oxygen vacancies due to reduction promotes the movement of atoms, the sintering reaction is promoted. Therefore, the zinc oxide-based sputtering target can produce a zinc oxide-based sputtering target having a lower resistivity in the entire region in the target thickness direction and a smaller variation in resistivity in the target thickness direction and in the sputtering surface.

  Therefore, according to the zinc oxide-based sputtering target of the present invention, since the target resistivity is low in the entire region in the thickness direction and becomes uniform in the target surface, stable DC sputtering is always possible. Contributes to improved performance.

It is a figure explaining the resistivity measurement of the sputtering surface direction of a sputtering target.

  Next, the zinc oxide-based sputtering target and the method for producing the same of the present invention will be specifically described below with reference to examples.

〔Example〕
First, zinc oxide (ZnO) powder having a purity of 4N and an average particle diameter: D ₅₀ = 1.0 μm, aluminum oxide (Al ₂ O ₃ ) powder having a purity of 4N and an average particle diameter of D ₅₀ = 0.2 μm, purity 4N A gallium oxide (Ga ₂ O ₃ ) powder having an average particle diameter of D ₅₀ = 1.7 μm and an indium oxide (In ₂ O ₃ ) powder having a purity of 4N and an average particle diameter of D ₅₀ = 1.0 μm were prepared. Each of these powders was weighed so as to have the composition shown in Table 1 and placed in a ball mill apparatus. At this time, with respect to 100 kg of the weighed powder: 35 kg of pure water, as a dispersant for dispersing the powder, amide amine salt of high molecular weight polyester acid (manufactured by Enomoto Kasei Co., Ltd.): 1.5 kg of polyvinyl As an alcohol binder, 10 kg of modified PVA (manufactured by Nippon Vinegar Poval Co., Ltd.) was filled in each ball mill apparatus. Furthermore, 500 kg of zirconia balls having a diameter of 10 mm were added, and the above weighed powders were mixed.

  The slurry obtained by this ball mill mixing was dried and granulated using, for example, a spray dryer manufactured by Okawara Chemical Industries Co., Ltd. (FOC-35). Here, for this dry granulation, a spray dryer that can set the hot air temperature to 250 ° C. and the exhaust temperature to about 100 ° C. may be used. The spray discharge conditions and hot air temperature were adjusted to obtain granulated granules having an average particle size of 70 ± 30 μm.

Using this obtained granulated granule, 150 MPa and pressurization for 5 minutes were carried out with a cold isostatic press (CIP) machine to produce a green compact. This powder compact was inserted into a heating furnace. Here, heating was started and the degreasing process was started. In this degreasing step, the temperature is raised to 600 ° C. in an atmospheric atmosphere at normal pressure, and the dispersant and binder in the green compact are burned to perform degreasing. Next, while heating the atmosphere in the heating furnace, the temperature of the heating furnace is further increased, and the process proceeds to the sintering step. When moving to this sintering step, the atmosphere was switched from an atmospheric atmosphere to a non-oxidizing (reducing) gas (gas injection timing) to make a non-oxidizing atmosphere. As this non-oxidizing atmosphere, nitrogen (N ₂ ) gas or argon (Ar) gas was introduced, or a vacuum atmosphere was adopted. The amount of gas introduced was 3 L / min. In this sintering step, the temperature was further raised and heated to 1350 ° C. Thereafter, the temperature was maintained at 1350 ° C. for 5 hours. After elapse of this holding time, the heating furnace was cooled to 600 ° C., and the sintering process was completed. And it took out from the heating furnace, the sintered compact was machined, and the zinc oxide type | system | group sputtering target of Examples 1-3, 5-7 and Reference Example 4 which has a diameter of 152.4 mm was produced. In the sintering step of Example 1 to 3 and 5, the nitrogen gas, and, in the sintering process of Example 6, an argon gas was introduced, respectively. Moreover, in the sintering process of Example 7, it switched to the vacuum atmosphere.

[Comparative Example]
In order to compare with the zinc oxide type sputtering target of the said Example, the zinc oxide type sputtering target of Comparative Examples 1-3 shown by Table 1 was prepared. As in the case of Example 2, all of Comparative Examples 1 to 3 are cases where zinc oxide powder and aluminum oxide powder are mixed, and the amount of aluminum oxide powder added is 1.6 at%. . In the case of Comparative Example 1, the timing of introducing the non-oxidizing gas is after holding at a high temperature at 1350 ° C., and in the case of Comparative Example 2, the timing is the start of temperature rise for the degreasing process, and In the case of Comparative Example 3, the non-oxidizing gas was not charged and the oxidizing gas atmosphere was maintained.

<Measurement of resistivity>
About the obtained Example 1-3, 5-7, the reference example 4, and the zinc oxide type | system | group sputtering target of Comparative Examples 1-3, the thickness direction (corresponding to the erosion depth) from the processed surface (surface) ), The resistivity was measured with a resistance measuring device. Here, a zinc oxide-based sputtering target having a diameter of 152.4 mm × thickness of 10 mm was produced by the above-described manufacturing method, and the surface (0 mm) was shaved from the surface (0 mm) to 2 mm, 4 mm, 6 mm, and 8 mm. The resistivity was measured. The maximum difference in resistivity in the erosion depth direction was determined from the measured maximum and minimum resistivity values at each depth. The above results are shown in Table 2.
In addition, a cylindrical zinc oxide sputtering target having an outer diameter of 155 mm, an inner diameter of 135 mm, and a length of 200 mm was produced under the same conditions as in Example 2 to obtain Example 8. This was cut in the erosion depth direction from the surface (0 mm) to 2 mm, 4 mm, 6 mm, and 8 mm, and the resistivity was measured. The maximum difference in resistivity in the erosion depth direction was determined from the measured maximum and minimum resistivity values at each depth. The above results are shown in Table 3.

In addition, on the surfaces (0 mm) of the zinc oxide based sputtering targets of Examples 1 to 3 and 5 to 7, Reference Example 4 and Comparative Examples 1 to 3, five points (A in the target sputtering surface as shown in FIG. The resistivity was measured for the measurement points (E) to (E). The maximum difference in resistivity within the sputtering surface was determined from the measured maximum and minimum values of resistivity within the surface. The measurement results are shown in Table 3.
In this measurement, a resistivity (Ω · cm) was measured by a four-probe method using a low resistivity meter (Loresta-GP) manufactured by Mitsubishi Chemical Corporation as a resistance measuring device. The measurement temperature was 23 ± 5 ° C. and the humidity was 50 ± 20%.

<Measurement of abnormal discharge times>
About the obtained Examples 1-3, 5-7, the reference example 4, and the zinc oxide type | system | group sputtering target of Comparative Examples 1-3, the frequency | count of abnormal discharge generation | occurrence | production at the time of sputtering was measured.
Using the zinc oxide based sputtering targets of Examples 1 to 3 and 5 to 7, Reference Example 4 and Comparative Examples 1 to 3, film formation tests were performed under the following film formation conditions.
・ Power supply: DC1000W
・ Total pressure: 0.4Pa
Sputtering gas: Ar = 45 sccm, O ₂ : 5 sccm
-Target-substrate (TS) distance: 70 mm
Sputtering was performed for 1 hour under the above film formation conditions, and the number of occurrences of micro-arc abnormal discharge was automatically measured by an arcing counter attached to the sputtering power supply. Further, sputtering of the target was performed, and sputtering was performed for 1 hour in the same manner from the time when the depth of the erosion portion reached 2 mm, 4 mm, 6 mm, and 8 mm from the surface, and the number of occurrences of abnormal discharge was measured. The measurement results are shown in Table 5.

According to the results shown in the above tables, the resistivity of each of the zinc oxide-based sputtering targets of Examples 1 to 3 and 5 to 7 is 0.0001 to over the entire target thickness direction. In the range of 0.005 Ω · cm, the maximum difference in resistivity in the thickness direction is 0.003 Ω · cm or less, and the resistivity within the sputtering surface can achieve a maximum difference of 0.003 Ω · cm or less. As a result, it was found that the target resistivity was lower and the variation was small over the entire thickness direction of the target. Furthermore, in the sputtering using the zinc oxide-based sputtering targets of Examples 1 to 3 and 5 to 7 as described above, almost no abnormal discharge was generated. Therefore, it was found that the target resistivity could be uniformly reduced throughout the target thickness direction and within the sputtering surface, so that stable DC sputtering was always possible. Also, the cylindrical zinc oxide sputtering target of Example 8 has a resistivity in the range of 0.0001 to 0.005 Ω · cm, and the maximum difference in the thickness direction of the resistivity is also 0.003 Ω · cm or less. As a result, it was confirmed that no abnormal discharge occurred even in sputtering using this sputtering target.

On the other hand, with respect to zinc oxide-based sputtering targets of Comparative Examples 1 to 3, a green compact made of a mixture of raw material powder to degreasing step being degreased in an oxidizing atmosphere, Example 1～3,5～ 7 , but in the subsequent reduction process, in Comparative Example 1, since the non-oxidizing gas was introduced at a high temperature at 1350 ° C., the resistivity increased inside the target, Discharge occurred frequently. In Comparative Example 2, the timing was set at the start of temperature increase for the degreasing process, so degreasing did not proceed in the nitrogen gas atmosphere, and organic matter remained, but the reduction proceeded to the inside, and the maximum difference in resistivity However, abnormal discharge occurred frequently during sputtering. In Comparative Example 3, the non-oxidizing gas was not charged during sintering and the oxidizing gas atmosphere was maintained, so the maximum difference in resistivity was large, and the resistivity could not be lowered, resulting in abnormalities during sputtering. Discharge occurred frequently. None of the zinc oxide-based sputtering targets of Comparative Examples 1 to 3 can perform DC sputtering stably because the target resistivity cannot be uniformly reduced throughout the target thickness direction and within the sputtering surface. There wasn't.

As described above, in the zinc oxide-based sputtering target according to the present invention, even if the shape of the green compact and the zinc oxide-based sintered body is a flat plate or the shape thereof is a cylindrical shape, the thickness thereof A low resistivity can be realized in the entire direction.

Claims (3)

A zinc oxide-based sintered body containing zinc oxide as a main component and including one or more metal oxides selected from Al and In as a component composition,
The zinc oxide-based sintered body has a target thickness of 10 mm or more, a resistivity of 0.0001 to 0.005 Ω · cm, and a maximum difference in resistivity in the target thickness direction of 0.00011. A sputtering target for DC sputtering, wherein the sputtering target is 0.003 Ω · cm . 2. The sputtering target for DC sputtering according to claim 1, wherein the zinc oxide-based sintered body has a maximum difference in resistivity within a sputtering plane of 0.00013 to 0.003 Ω · cm . A degreasing step of degreasing the powder compact formed of zinc oxide powder and one or more metal oxide powders selected from Al and In while heating in an oxidizing atmosphere;
Heating temperature: Sintering step of reducing zinc oxide by switching from an oxidizing atmosphere to a non-oxidizing atmosphere at 500 to 700 ° C. and subjecting the degreased green compact to normal pressure sintering at 1200 to 1500 ° C. ,
The manufacturing method of the sputtering target for DC sputtering characterized by having.