JP4483470B2 - Method for producing sputtering target containing indium oxide - Google Patents

Description

  The present invention is widely used as a transparent conductive film such as a flat panel display, and relates to a sputtering target manufacturing method for obtaining an oxide film containing indium oxide.

  As a transparent conductive film for a flat panel display or the like, low resistance and high transmittance are required, and an oxide film containing indium oxide is used to meet 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 transmittance for visible light. Further, in recent years, there have been increased cases in which metal oxides other than indium oxide are added to indium oxide and oxide films containing indium oxide having various characteristics are used. In forming such an oxide film, since a film having a large area can be obtained, film formation by sputtering is generally mainstream, and a sputtering target is often used for the film formation.

  The sputtering target is manufactured by several methods such as a dry pressure molding method and a cast molding method.

  Among these, in the dry pressure molding method, water, an organic binder, a plasticizer, and the like are mixed with raw material powder having an average particle size of about 0.5 to 2 μm, and then granules of several tens to several hundreds of μm (granulated powder). ), Filled in a mold or rubber, etc., and pressed using a uniaxial press or CIP (cold isostatic press), usually at a pressure of 100 to 300 MPa, and molded into a predetermined shape, and then obtained. A sputtering target is obtained by sintering and processing the body.

  In many cases, the granulated powder is prepared by mixing water with raw material powder and an organic binder, dispersant, plasticizer, etc. to prepare a slurry, and spray-drying the resulting slurry using a spray dryer. It is obtained by.

  Generally, PVA (polyvinyl alcohol) is used as an organic binder to be added. In this case, 1 to 10% by mass of PVA is usually added to the raw material powder.

  However, indium oxide is very strongly agglomerated and is a heavy raw material powder. Therefore, the viscosity of the slurry is high and the sedimentation of the raw material powder is fast. Therefore, it is difficult to perform spray drying, and both the efficiency of the spray drying process and the yield of the granulated powder are deteriorated.

  In order to compensate for these problems, a dispersant is added during the preparation of the slurry.

As a dispersing agent to be used, polyacrylic acid Na salt or NH ₃ salt is generally used. However, these contain a large amount of impurities, adversely affect the properties of the resulting film, and the effect of indium oxide dispersion is insufficient.

  Furthermore, since the granulated powder contains many pores, the shrinkage becomes large at the time of CIP molding, and cracks occur in the molded body at the time of molding pressure reduction, and the yield of the obtained sputtering target tends to be lowered.

  In order to solve these problems, it is necessary to further improve the strength of the molded body. To increase the strength of the molded body, it is effective to increase the amount of the organic binder. However, in this case, there arises a problem that it is difficult to control the size of the molded body due to the reason that the degreasing time becomes long, the density of the product after baking becomes low, or the baking shrinkage becomes large. End up.

  In addition, the granulated powder becomes too hard, the granulated powder is not easily deformed during pressure molding, the density of the molded body is lowered, and conversely, the strength may be reduced (see Patent Document 1, paragraphs 0002 to 0011). ).

On the other hand, a high-strength oxide-based ceramic molded body using a polyacrylic polymer represented by the following chemical formula as an organic binder has been proposed (see Patent Document 1, paragraph number 0018).

  However, even if a sputtering target containing indium oxide is obtained using such a polyacrylic polymer, the above problem cannot be solved sufficiently. Because a sufficient dispersion effect cannot be obtained, even if a slurry is prepared using a polyacrylic polymer as an organic binder, it is impossible to obtain a slurry that can prevent precipitation of indium oxide and can be efficiently spray-dried. In addition, since the granulated powder obtained by spray-drying such a slurry with a spray dryer contains many pores, the tap density is low, and the air taken into the compact at the time of molding pressure reduction is low. In many cases, the molded body is cracked by the stress applied when it goes out of the molded body or the stress generated during decompression. Furthermore, the polyacrylic polymer is more expensive than the PVA.

  The present inventors have so far proposed an efficient method for directly forming a granulated powder by CIP as disclosed in JP-A-2003-3257. Even if a molded product is obtained, the tap density of the granulated powder cannot be adjusted to a high level, and the shrinkage during molding becomes large, and it is difficult to improve the strength of the molded product by quantitative adjustment. Is particularly likely to occur.

JP-A-8-277168

JP 2003-3257 A

  An object of the present invention is to provide a method for efficiently obtaining a sputtering target having a high density with high production efficiency in a method for producing a sputtering target for obtaining an oxide film containing indium oxide.

  The method for producing a sputtering target containing indium oxide according to the present invention comprises preparing a slurry by mixing and pulverizing water, an organic binder, and a dispersant in a metal oxide raw material powder containing indium oxide powder. In accordance with a production method for obtaining a sputtering target by drying and spraying to obtain granulated powder, press-molding the obtained granulated powder, and firing the obtained molded body, the dispersant is acrylic acid It is a methacrylic acid copolymer ammonia neutralized product.

  Thereby, polyvinyl alcohol can be used as the organic binder.

  It is preferable that the addition amount of the acrylic acid / methacrylic acid copolymer ammonia neutralized product is in the range of 0.1 to 3% by mass with respect to the raw material powder.

  Thereby, even if the raw material powder concentration in the slurry is 60% or more, the slurry viscosity can be less than 100 cps.

  According to the present invention, an excellent sputtering target having a sufficiently high density can be obtained. In addition, since the slurry concentration can be increased in the manufacturing process, the production efficiency is improved. Moreover, since the crack of the molded object at the time of shaping | molding can also be reduced, the yield of a sputtering target can be improved.

  Furthermore, since a general and inexpensive polyvinyl alcohol (PVA) can be used as the organic binder, the sputtering target can be manufactured at a low cost.

  Since indium oxide is difficult to sinter, the particle size is adjusted so that the average particle size of both primary particles and secondary particles is less than 1 μm, and the sinterability is often improved. Therefore, in the manufacturing process of granulated powder, when particles are atomized, the aggregation of particles in the slurry becomes strong and the slurry viscosity increases. Further, the indium oxide powder is relatively heavy particles, the sedimentation in the slurry is fast, and it is difficult to obtain a uniform slurry.

  In the present invention, an acrylic acid / methacrylic acid copolymer ammonia neutralized product is used as a dispersing agent in the granulated powder production process.

Specifically, an acrylic acid-methacrylic acid copolymer ammonia neutralized product represented by the following chemical formula is used.

Since it is acrylic acid-based and neutralized with NH ₃ salt, it has excellent dispersion ability. Thereby, aggregation of indium oxide is suppressed and a uniform slurry can be obtained. The addition amount is 0.1-3 mass% with respect to the total amount of indium oxide powder and addition oxide powder. If the amount is less than 0.1% by mass, the dispersion capacity is poor, and if it exceeds 3% by mass, the volatile matter increases during sintering, and thus the probability that the product breaks during sintering will increase.

  When the dispersant is not used, even if the raw material powder concentration is about 30 to 35%, the slurry viscosity exceeds 100 cps. However, by using the neutralized product of acrylic acid / methacrylic acid copolymer ammonia, Even if the concentration is about 70%, the viscosity becomes less than 100 cps, and the precipitation in the indium oxide is suppressed, so that the efficiency in the spray drying process is remarkably improved.

  When an acrylic acid / methacrylic acid copolymer ammonia neutralized product is used as a dispersant, polyvinyl alcohol (PVA) is sufficient as the added organic binder from the viewpoint of the strength of the molded product. PVA having a saponification degree of 90 to 97 mol 1% and a polymerization degree of 400 to 1000 is suitable. By using PVA having a saponification degree and a polymerization degree within this range, the resulting granulated powder becomes soft and the crushability at the time of 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 exceeding 97mo1% or a polymerization degree exceeding 1000%, the collapsibility of the granulated powder at the time of molding deteriorates, voids in the molded body increase, and the molded body strength decreases. However, it is not preferable because the density of the sputtering target obtained after sintering is not improved.

  In addition, use of PVA having a saponification degree of less than 90 mol% or a polymerization degree of less than 400 is not preferable because the molded article becomes too soft and the working efficiency deteriorates.

  The amount of the organic binder is 1.0 to 3.0% by mass with respect to the total amount of the indium oxide powder and the added oxide powder. If it is less than 1.0% by mass, the strength of the molded product will be reduced, and the probability of cracking in the steps after molding will increase. If it exceeds 3.0% by mass, voids generated by the binder will increase, Even grain growth is not preferable because it becomes difficult to eliminate voids and the product density decreases. In addition, since the volatile content increases during sintering, the possibility of the product breaking increases.

  When spray-drying the slurry to which the acrylic acid / methacrylic acid copolymer neutralized product and PVA are added, it is desirable to set the drying temperature to 130 to 200 ° C. When dried above 200 ° C., the granulated powder becomes hard, and vacancies are likely to occur during molding, and the density of the sputtering target is difficult to improve.

  It is recognized that the tap density of the granulated powder is improved when the acrylic acid / methacrylic acid copolymer ammonia neutralized product is used as a dispersant, because aggregation is removed and compared with the case where it is not used. .

  Regarding the molding, the present inventor has proposed an efficient method of directly molding the granulated powder by CIP in the above-mentioned Japanese Patent Application Laid-Open No. 2003-3257, but this molding method is used according to the present invention. It became possible enough. The molding pressure is desirably 100 to 300 MPa. If it is less than 100 MPa, the product yield due to a decrease in the density of the green body and the strength of the green body deteriorates, which is not preferable.

  Sintering is desirably performed at 1100 ° C. or higher where grain growth of indium oxide powder is expected. However, when the temperature exceeds 1600 ° C., the reaction with the furnace material becomes violent and the volatilization becomes violent.

  Next, the present invention will be further described using examples.

(Examples 1-12)
37.5 g of indium oxide powder and the added oxide powder shown in Table 1, a saponification degree of 94 mol%, and a polymerization degree of polyvinyl alcohol of 500 mol to a total raw material powder of 1.25 mass%, The total raw material powder 3000g was adjusted to 48g so that it might become 0.25-4 mass% with respect to a total raw material powder, acrylic acid methacrylic acid copolymer ammonia neutralized material (Chubu Seiden make, Banstar X754B). These and 2000 g of pure water were put into a 10 L pot, and ball mill mixing and pulverization were carried out at a rotational speed of 60 rpm for 15 to 20 hours to prepare a slurry. The slurry concentration was 60% by mass.

  Next, the obtained slurry was spray-dried with a spray dryer to obtain granulated powder. In this process, although the slurry concentration was as high as 60% by mass, there was no phenomenon that the raw material powder settled in the slurry, and the granulated powder was efficiently obtained.

The obtained granulated powder was put into a rectangular rubber mold shown in the above-mentioned JP-A No. 2003-3257 and pressurized at 294 MPa (3 ton / cm ² ) to produce a molded body of 300 × 300 × 10 mm. . Subsequently, it baked in 1500 degreeC for 20 hours in oxygen atmosphere, the sintered compact was obtained, it processed, and the sputtering target was obtained.

  The product relative density of the obtained sputtering target was calculated | required by the measurement of mass and a dimension. The results are shown in Table 1.

  It can be seen from Table 1 that a target having a sufficient relative density can be obtained by setting an appropriate amount of the dispersant.

  It can also be seen that a sputtering target can be sufficiently produced even by a molding method that requires strength because the granulated powder is directly filled into the rubber mold.

(Comparative Examples 1-3)
Indium oxide powder, and the oxide powder shown in Table 2, polyvinyl alcohol having a saponification degree of 94 mol% and a polymerization degree of 500, 37.5 g so as to be 1.25% by mass with respect to the total raw material powder, The raw material powder 3000g was adjusted. These and 7000 g of pure water were put into a 10 L pot, and were mixed and pulverized for 15 to 20 hours at a rotation speed of 60 rpm to prepare a slurry. The slurry concentration is 30% by mass.

Next, the obtained slurry was spray-dried with a spray dryer to obtain granulated powder. The obtained granulated powder was put into a rectangular rubber mold shown in the above-mentioned JP-A No. 2003-3257 and pressurized at 294 MPa (3 ton / cm ² ) to produce a molded body of 300 × 300 × 10 mm. .

  However, cracks occurred in all the molded bodies.

  From Table 2, it is understood that in Comparative Examples 1 to 3, it is difficult to produce a sputtering target because it is difficult to mold.

Claims (4)

The raw material powder of metal oxide containing indium oxide powder is mixed and pulverized with water, an organic binder and a dispersant to prepare a slurry, and the slurry is dried and sprayed to obtain a granulated powder, and the resulting granulated product In the production method for obtaining a sputtering target by pressure-molding the powder and firing the obtained molded body, the dispersant is an acrylic acid / methacrylic acid copolymer ammonia neutralized product represented by the following chemical formula: A method for producing a sputtering target containing indium oxide, characterized in that the raw material powder concentration in the slurry is 60% or more and the slurry viscosity is less than 100 cps .

  The method for producing a sputtering target containing indium oxide according to claim 1, wherein the organic binder is polyvinyl alcohol.   3. The indium oxide according to claim 1, wherein an addition amount of the acrylic acid / methacrylic acid copolymer neutralized product is in a range of 0.1 to 3 mass% with respect to the raw material powder. The manufacturing method of the sputtering target containing this. The method for producing a sputtering target containing indium oxide according to any one of claims 1 to 3, wherein the slurry viscosity is 50 cps or less.