JP4508079B2 - Manufacturing method of sputtering target - Google Patents

Description

  The present invention relates to a method for producing a sputtering target containing zinc oxide. An oxide film manufactured using the sputtering target can be used as a transparent conductive film such as a flat panel display.

  Transparent conductive films such as flat panel displays are required to have characteristics such as low resistance and high transmittance. At present, oxide films containing indium oxide are used to satisfy the characteristics. . In particular, an ITO film in which tin oxide is added to indium oxide is widely used because of its low resistance and high visible light transmittance.

  Such an oxide film is also required to have a large area. For this reason, a sputtering method is generally used in forming such an oxide film. In film formation by a sputtering method, a sputtering target is used.

  However, indium raw materials are rare metals, and there is a concern about securing a stable supply amount. In addition, soaring indium prices are also a problem. For this reason, development of a transparent conductive film containing no indium has been strongly demanded.

  As a transparent conductive film containing no indium, an oxide film using zinc oxide is considered promising because it has a low resistance and high transmittance close to those of an ITO film, and is currently being used. In the film formation, the sputtering method is mainly used as in the case of the ITO film formation. As a sputtering target to be used, a sputtering target prepared by adding an oxide such as boron oxide, aluminum oxide, or gallium oxide to zinc oxide has been proposed (see, for example, Patent Documents 1 to 3).

  Sputtering targets are generally produced by dry pressure molding, cast molding, etc., but the dry pressure molding method is superior in production stability because of high strength of the molded body, and shape stability. Excellent because it is excellent in terms of high yield.

  In the dry pressure molding method, granules (granulated powder) of several tens to several hundreds of μm produced from raw material powder having an average particle size of about 0.5 to 2 μm are filled into a mold or a rubber mold and uniaxial press or It is formed into a predetermined shape by CIP (cold isostatic pressing). The pressurizing pressure is usually 100 to 300 MPa. A sputtering target can be obtained by sintering and processing the obtained molded body.

  The granulated powder can be obtained from a slurry obtained by adjusting the amount of raw material powder, organic binder, dispersant and the like and mixed with water. Generally, the slurry is sprayed using a spray dryer, It can be obtained by drying. As the organic binder, PVA (polyvinyl alcohol) is generally used. In this case, 1 to 10% by mass of PVA is usually added to the raw material powder.

  On the other hand, when producing granulated powder mainly composed of zinc oxide, if the raw material powder is not very fine, it is possible to increase the amount of water used and reduce the viscosity of the slurry without adding a dispersant. Granulated powder can be obtained. This is because zinc oxide is excellent in sinterability.

  A sputtering target has been conventionally produced using the granulated powder thus produced, and a high-density sputtering target has also been produced. However, due to the low slurry concentration, the efficiency of the spray drying process was very poor. The slurry concentration is the ratio of the total mass of raw material powder, organic binder, and dispersant, which are constituent components other than water as a solvent, to the total mass of the slurry.

  Further, in order to enable stable film formation by sputtering, it is necessary to further improve the density of the sputtering target. For this purpose, it is necessary to further improve the sinterability by making the zinc oxide powder into a fine powder. However, when the zinc oxide powder is made into a fine powder, the aggregation of the zinc oxide powder becomes stronger and the viscosity of the slurry becomes higher. Therefore, it is necessary to add a dispersant when preparing the granulated powder. The dispersing agent used in this case is a sodium salt or ammonium salt of polyacrylic acid.

  However, when the sodium salt of polyacrylic acid is used, sodium is mixed as an impurity in the resulting film, which adversely affects the characteristics of the film. Moreover, when the ammonium salt of polyacrylic acid was used, the dispersion effect was insufficient and the dispersion of the zinc oxide powder was insufficient.

  Moreover, when the ammonium salt of polyacrylic acid is used, since the obtained granulated powder contains many voids, the shrinkage increases during CIP molding. For this reason, when reducing a press pressure after CIP shaping | molding, it became easy to generate | occur | produce a crack in a molded object and the yield of the sputtering target obtained also worsened.

JP 2000-178725 A JP 2001-73122 A JP 2004-175616 A

  The present invention has been made in view of such a problem, and is a sputtering target containing zinc oxide, which has a high density and is less contaminated with impurities. The object is to provide a method of manufacturing.

  A method for producing a sputtering target according to the present invention includes a step of mixing a metal oxide powder containing zinc oxide powder with water, an organic binder, and a dispersant to obtain a slurry, and spraying and drying the obtained slurry. The step of obtaining granulated powder, the step of pressing the obtained granulated powder to obtain a molded body, the step of firing the obtained molded body to obtain a sintered body, and the obtained sintering A sputtering target having a step of obtaining a sputtering target by using a neutralized acrylic acid / methacrylic acid copolymer ammonia as the dispersant. The method for producing a sputtering target according to the present invention is not limited, but is particularly applicable when the metal oxide powder contains 70% by mass or more of zinc oxide powder with respect to the total mass of the powder. Is done.

  The addition amount of the acrylic acid / methacrylic acid copolymer ammonia neutralized product is preferably 0.3 to 3% by mass relative to the total mass of the metal oxide powder.

  Thereby, even if the total mass of the metal oxide powder, the organic binder, and the neutralized acrylic acid / methacrylic acid copolymer ammonia is 60% by mass or more based on the total mass of the slurry, The viscosity can be less than 100 cps.

  For example, polyvinyl alcohol can be used as the organic binder.

  In the present invention, an acrylic acid / methacrylic acid copolymer ammonia neutralized product is used as a dispersant, so that a zinc oxide powder having a small particle diameter can be used as a raw material powder, and a sufficiently high density sputtering target can be used. Obtainable. Moreover, the crack of the molded object at the time of shaping | molding can also be reduced, and the yield of a sputtering target can also be improved. Furthermore, since the density | concentration of the slurry used for granulated powder manufacture can be enlarged, production efficiency will also become favorable.

  Further, since polyvinyl alcohol (PVA) that is easily available and inexpensive can be used as the organic binder, the sputtering target can be manufactured at low cost.

  A method for producing a sputtering target according to the present invention includes a step of mixing a metal oxide powder containing zinc oxide powder with water, an organic binder, and a dispersant to obtain a slurry, and spraying and drying the obtained slurry. The step of obtaining granulated powder, the step of pressing the obtained granulated powder to obtain a molded body, the step of firing the obtained molded body to obtain a sintered body, and the obtained sintering Processing the body to obtain a sputtering target. And as a dispersing agent used for manufacture of a slurry, the acrylic acid methacrylic acid copolymer ammonia neutralized material shown to following Chemical formula 1 is used, It is characterized by the above-mentioned.

  Since the dispersant is acrylic acid-based and neutralized with ammonia to form an ammonium salt, the dispersant has excellent dispersibility. For this reason, aggregation of zinc oxide is effectively suppressed and a uniform slurry can be obtained.

  The addition amount of the dispersant is preferably 0.3 to 3% by mass with respect to the total mass of the metal oxide powder including the zinc oxide powder. By setting the addition amount to 0.3 to 3% by mass, even if the concentration of the slurry is about 70% by mass, the viscosity of the slurry becomes less than 100 cps, and spraying in the spray drying process becomes easy. Moreover, since the precipitation of zinc oxide powder can be suppressed by the addition of the dispersant, the efficiency in the spray drying process is remarkably improved.

  When the added amount of the dispersing agent is less than 0.3% by mass, the dispersing ability may be insufficient. When the dispersant is not used, even if the slurry has a concentration of about 30 to 35% by mass, the viscosity becomes 100 cps or more, and spraying in the spray drying process becomes difficult. On the other hand, if the amount of the dispersant added is greater than 3% by mass, the volatile content increases during sintering, and the probability that the product will break during sintering increases.

  As the organic binder to be added, when a neutralized acrylic acid / methacrylic acid copolymer is used as a dispersant, the dispersion capacity becomes very high, so polyvinyl alcohol (PVA) is sufficient, and the molded body has sufficient strength. Is obtained. As the PVA to be used, those having a saponification degree of 90 to 97 mol 1% and a polymerization degree of 400 to 1000 are suitable. By using PVA having a saponification degree and a polymerization degree within this range, the resulting granulated powder becomes moderately soft and the crushability during molding is improved. As a result, voids in the molded body are reduced, the molded body strength is improved, and the density of the sputtering target obtained by firing is improved.

  If PVA with a saponification degree of more than 97 mo 1% or a polymerization degree of more than 1000 is used, the pulverization property of the granulated powder at the time of molding deteriorates, voids in the molded body increase, and the molded body strength decreases. . Moreover, the density of the sputtering target obtained after sintering is not improved. On the other hand, when PVA having a saponification degree of less than 90 mo 1% or a polymerization degree of less than 400 is used, the molded article becomes too soft, resulting in poor working efficiency.

  In the present invention, it is sufficient to use PVA as the organic binder, but it is also possible to use an acrylic binder in addition to PVA.

  The amount of the organic binder is preferably 1.0 to 3.0% by mass with respect to the total mass of the metal oxide powder including zinc oxide powder. When it is less than 1.0% by mass, the strength of the molded body is lowered, and the probability of cracking in the steps after molding is increased. On the other hand, even if the amount is more than 3.0% by mass, voids generated by the organic binder become large. Therefore, even if grain growth is performed during sintering, it is difficult to eliminate the voids, and the density of the obtained sputtering target is low. It will decline. In addition, since the volatile content increases during sintering, the possibility of the product breaking increases.

  When the slurry obtained by adding zinc oxide powder, other metal oxide powder, neutralized acrylate / methacrylic acid copolymer ammonia and PVA to water is sprayed and dried to produce granulated powder, drying temperature Is preferably 130 to 200 ° C. When the drying temperature is less than 130 ° C., the moisture content of the granulated powder increases and the strength of the molded body decreases. On the other hand, when the drying temperature is higher than 200 ° C., the granulated powder becomes hard, and voids are likely to occur during molding, so that the density of the sputtering target is hardly improved.

  The molding pressure when the obtained granulated powder is molded into a predetermined shape by uniaxial pressing or CIP (cold isostatic pressing) is preferably 100 to 300 MPa. When the molding pressure is less than 100 MPa, the density of the molded body and the strength of the molded body are lowered, and the product yield is deteriorated. On the other hand, even if the molding pressure is greater than 300 MPa, the effect on the compact density and the compact strength hardly changes.

  The sintering temperature for sintering the obtained molded body is preferably 1000 ° C. or higher at which the grain growth of the zinc oxide powder can be expected. However, if the sintering temperature is higher than 1500 ° C., the reaction between the molded body and the furnace material and the volatilization of volatile components in the molded body become violent, which is not preferable.

(Examples 1-12)
Table 1 shows the content ratio of the zinc oxide powder, the type and content ratio of the other metal oxide powder, the content ratio of polyvinyl alcohol used as the binder, and the content ratio of the neutralized methacrylic acid copolymer ammonia. Each material used in each example was blended as shown in FIG. In addition, the total mass of the metal oxide powder containing zinc oxide powder is 3000 g, and the content ratio of each material is a ratio with respect to the total mass of 3000 g of the metal oxide powder containing zinc oxide powder.

  Polyvinyl alcohol having a saponification degree of 94 mol% and a polymerization degree of 500 was used as the polyvinyl alcohol, and Banstar X754B manufactured by Chubu Seiden Co., Ltd. was used as the neutralized methacrylic acid copolymer ammonia. Polyvinyl alcohol is blended in an amount of 37.5 g so as to be 1.25% by mass with respect to a total mass of 3000 g of the metal oxide powder including zinc oxide powder, and the neutralized methacrylic acid copolymer ammonia is zinc oxide. 7.5-120g was mix | blended so that it might become 0.25-4.0 mass% with respect to 3000g of total mass of the metal oxide powder containing powder.

  A total mass of 3000 g of metal oxide powder including zinc oxide powder, a predetermined amount of polyvinyl alcohol, a predetermined amount of neutralized acrylic acid / methacrylic acid copolymer ammonia, and 2000 g of pure water are placed in a 10 L pot and rotated. A slurry was prepared by mixing and pulverizing with a ball mill at several 60 rpm for 15 to 20 hours. The concentration of the resulting slurry is shown in Table 1. Moreover, the viscosity of each slurry of Examples 1-12 was measured using the B-type viscometer. The measurement results are shown in Table 1.

  Next, the obtained slurry was sprayed with a spray dryer and dried to produce granulated powder. In this process, although the slurry concentration exceeded 60% by mass, there was no phenomenon that the raw material powder settled in the slurry, and the granulated powder could be produced efficiently.

The obtained granulated powder was put into a rectangular rubber mold shown in FIGS. 1 and 2 and pressed at 294 MPa (3 ton / cm ² ) to produce a molded body of 300 × 200 × 10 mm. 1 and 2, reference numerals 1 and 3 indicate plate-like rubber molds, reference numeral 2 indicates a cylindrical rubber mold, and reference numeral 4 indicates granulated powder.

  The molded body produced as described above was fired at 1300 to 1400 ° C. for 15 hours in an oxygen atmosphere to obtain a sintered body.

  The appearance of the obtained molded body and sintered body was observed, and whether or not cracks occurred was examined for 5 samples for each example. It was judged that a good product of the sintered body was obtained when no cracks occurred in the molded body and the sintered body. Table 1 shows the yield rate of the sintered body.

  Next, the obtained sintered body was processed to produce a sputtering target. When the mass and dimension of the obtained sputtering target were measured and the relative density of the sputtering target was calculated, all were 95% or more.

(Examples 13 to 15)
Table 1 shows the content ratio of the zinc oxide powder, the type and content ratio of the other metal oxide powder, the content ratio of polyvinyl alcohol used as the binder, and the content ratio of the neutralized methacrylic acid copolymer ammonia. Each material used in each example was blended as shown. In addition, the total mass of the metal oxide powder containing zinc oxide powder is 3000 g, and the content ratio of each material is a ratio with respect to the total mass of 3000 g of the metal oxide powder containing zinc oxide powder.

  Polyvinyl alcohol having a saponification degree of 94 mol% and a polymerization degree of 500 was used as the polyvinyl alcohol, and Banstar X754B manufactured by Chubu Seiden Co., Ltd. was used as the neutralized methacrylic acid copolymer ammonia. Polyvinyl alcohol is blended in an amount of 37.5 g so as to be 1.25% by mass with respect to a total mass of 3000 g of the metal oxide powder including zinc oxide powder, and the neutralized methacrylic acid copolymer ammonia is zinc oxide. 48-90g was mix | blended so that it might become 1.6-3.0 mass% with respect to 3000g of total mass of the metal oxide powder containing powder.

  A total mass of 3000 g of metal oxide powder containing zinc oxide powder, a predetermined amount of polyvinyl alcohol, a predetermined amount of neutralized acrylic acid / methacrylic acid copolymer ammonia, and 1280 g of pure water are placed in a 10 L pot and rotated. A slurry was prepared by mixing and pulverizing with a ball mill at several 60 rpm for 15 to 20 hours. The concentration of the resulting slurry is shown in Table 1. Moreover, the viscosity of each slurry of Examples 13-15 was measured using the B-type viscometer. The measurement results are shown in Table 1.

  Thereafter, granulated powder, a molded body, a sintered body, and a sputtering target were produced in the same manner as in Examples 1-12. Table 1 shows the yield rate of the sintered body. Moreover, when the mass and dimension of the obtained sputtering target were measured and the relative density of the sputtering target was computed, all were 95% or more.

(Comparative Examples 1-3)
Each material used in each example was blended so that the content of zinc oxide powder, the type and content of other metal oxide powders, and the content of polyvinyl alcohol were as shown in Table 1. In Comparative Examples 1-3, unlike Examples 1-15, the acrylic acid methacrylic acid copolymer ammonia neutralized material is not contained. In addition, the total mass of the metal oxide powder containing zinc oxide powder is 3000 g, and the content ratio of each material is a ratio with respect to the total mass of 3000 g of the metal oxide powder containing zinc oxide powder.

  As the polyvinyl alcohol, polyvinyl alcohol having a saponification degree of 94 mol% and a polymerization degree of 500 was used. 37.5 g of polyvinyl alcohol was blended so as to be 1.25% by mass with respect to 3000 g of the total mass of the metal oxide powder containing zinc oxide powder.

  A total mass of 3000 g of metal oxide powder including zinc oxide powder, a predetermined amount of polyvinyl alcohol, and 7000 g of pure water are put in a 10 L pot, mixed and pulverized in a ball mill at a rotation speed of 60 rpm for 15 to 20 hours, A slurry was prepared. The concentration of the resulting slurry is shown in Table 1. Moreover, the viscosity of each slurry of Comparative Examples 1-3 was measured using the B-type viscometer. The measurement results are shown in Table 1.

  Thereafter, granulated powder, a molded body, a sintered body, and a sputtering target were produced in the same manner as in Examples 1-12. Table 1 shows the yield rate of the sintered body. Moreover, when the mass and dimension of the obtained sputtering target were measured and the relative density of the sputtering target was computed, all were 95% or more.

(Comparative Examples 4-6)
In Comparative Examples 4 to 6, a conventionally used ammonium salt of polyacrylic acid was used as a dispersant, not a neutralized methacrylic acid copolymer ammonia.

  Comparison is made so that the content of zinc oxide powder, the type and content of other metal oxide powders, the content of polyvinyl alcohol, and the content of ammonium salt of polyacrylic acid are as shown in Table 1. Each material used in Examples 4 to 6 was blended. In addition, the total mass of the metal oxide powder containing zinc oxide powder is 3000 g, and the content ratio of each material is a ratio with respect to the total mass of 3000 g of the metal oxide powder containing zinc oxide powder.

  As the polyvinyl alcohol, polyvinyl alcohol having a saponification degree of 94 mol% and a polymerization degree of 500 was used. Polyvinyl alcohol is blended in an amount of 37.5 g so as to be 1.25% by mass with respect to 3000 g of the total mass of the metal oxide powder containing zinc oxide powder, and the ammonium salt of polyacrylic acid is a metal oxide containing zinc oxide powder. 7.5-90g was mix | blended so that it might become 0.25-3.0 mass% with respect to 3000g of total mass of a product powder.

  A total mass of 3000 g of metal oxide powder including zinc oxide powder, a predetermined amount of polyvinyl alcohol, a predetermined amount of ammonium salt of polyacrylic acid, and 2000 g of pure water are placed in a 10 L pot, and the rotational speed is 60 rpm. The slurry was prepared by mixing and grinding in a bead mill for ˜20 hours. The concentration of the resulting slurry is shown in Table 1. Moreover, the viscosity of each slurry of Comparative Examples 4-6 was measured using the B-type viscometer. The measurement results are shown in Table 1.

  Thereafter, granulated powder, a molded body, a sintered body, and a sputtering target were produced in the same manner as in Examples 1-12. Table 1 shows the yield rate of the sintered body. Moreover, when the mass and dimension of the obtained sputtering target were measured and the relative density of the sputtering target was computed, all were 95% or more.

  As can be seen from Table 1, in the sputtering target (Examples 1 to 15) produced using the production method according to the present invention, the concentration of the slurry used for granulated powder production was 60.4 to 71.0% by mass. Despite being large, the non-defective product ratio of the molded body and the sintered body is high, and both are 99% or more. Moreover, all the relative densities of the obtained sputtering target were 95% or more. Therefore, if the manufacturing method according to the present invention is used, a sputtering target having a high density can be efficiently produced. In particular, even in molding methods where the strength of the molded body is required because the granulated powder is directly filled into the rubber mold, such as a uniaxial press or CIP, the molded body is hardly cracked and has high production efficiency. It becomes possible to manufacture a sputtering target.

  In Comparative Examples 1 to 3 in which the neutralized acrylic acid / methacrylic acid copolymer was not contained, the viscosity of the slurry was as high as 900 to 1200 cps, although the slurry concentration was as small as 30% by mass. For this reason, although the relative density of the obtained sputtering target was all 95% or more, many cracks were generated at the stage of the molded body, and the non-defective product ratio was as low as about 90%.

  In addition, in Comparative Examples 4 to 6 using a conventionally used ammonium salt of polyacrylic acid instead of a neutralized acrylic acid / methacrylic acid copolymer as a dispersant, the slurry concentration is 60% by mass. The viscosity of the slurry was as high as 800 to 1400 cps. For this reason, although the relative density of the obtained sputtering target was all 95% or more, many cracks were generated at the stage of the molded body, and the yield of sintered bodies was as low as about 89%.

It is a rubber mold used to produce a compact by pressing the granulated powder. It is sectional drawing of the rubber mold shown in FIG.

Explanation of symbols

1, 3 Plate rubber mold 2 Cylindrical rubber mold 4 Granulated powder

Claims (4)

A step of obtaining a slurry by mixing water, an organic binder, and a dispersant with a metal oxide powder containing zinc oxide powder of 70% by mass or more, and spraying and drying the obtained slurry to obtain a granulated powder. A step, a step of press-molding the obtained granulated powder to obtain a molded body, a step of firing the obtained molded body to obtain a sintered body, and a sputtering process by processing the obtained sintered body A method for producing a sputtering target, comprising: using a neutralized acrylic acid / methacrylic acid copolymer ammonia represented by the following formula as the dispersant: Method.
  2. The sputtering target according to claim 1, wherein an addition amount of the acrylic acid / methacrylic acid copolymer ammonia neutralized product is 0.3 to 3% by mass with respect to a total mass of the metal oxide powder. Manufacturing method.   The total mass of the metal oxide powder, the organic binder, and the neutralized acrylic acid-methacrylic acid copolymer ammonia is 60% by mass or more based on the total mass of the slurry, and the viscosity of the slurry is The method for producing a sputtering target according to claim 1, wherein the sputtering target is less than 100 cps.   Polyvinyl alcohol is used as said organic binder, The manufacturing method of the sputtering target in any one of Claims 1-3 characterized by the above-mentioned.