JP4227227B2 - Manufacturing method of ITO sputtering target - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a target used for forming an ITO (indium-tin oxide) film by sputtering, and more particularly to a large ITO sputtering target.
[0002]
[Prior art]
The ITO film is known as a typical translucent conductive film, and is widely used in the field of optoelectronics such as a liquid crystal display and a transparent electrode of a solar cell. There are various methods for producing an ITO film, such as a spray method, a vacuum deposition method, an ion plating method, and a sputtering method. Among them, the sputtering method has attracted attention because of its high productivity. Furthermore, with the recent increase in demand for large liquid crystal displays, it has become necessary to increase the size of sputtering targets.
[0003]
[Problems to be solved by the invention]
As a method for producing an ITO sintered body as a target, a hot press method in which a hot press is applied to a molding process of a powder raw material, or a sintered compact obtained by press molding a powder raw material at room temperature, A cold press sintering method for performing machining is known. However, when the size of a sintered body is increased, the hot press method has a problem that there are large restrictions on the equipment and high initial cost. The cold press sintering method is an industrially used method, but has a problem that it is difficult to obtain a uniform sintered body density. Large targets, such as planar area exceeding 800 cm ² is usually used by laminating a plurality of sintered bodies obtained by processing, by using the non-uniform target density, thermal stress is generated during the bonding It tends to cause cracks and cracks. Also, if the target density is not uniform, there will be a difference in the etching rate of the target during sputtering, erosion may be uneven, blackening will start from the low density part, and nodules resulting from lower oxide will be generated. Thus, stable film formation cannot be obtained. Further, when a plurality of sheets are laminated, there is a problem that nodules and particles are likely to be generated at the laminated part. Accordingly, it has been desired to increase the size of one sintered body in order to reduce the number of laminated sheets as much as possible with a uniform density.
[0004]
In the conventional sintering furnace that sinters the molded body, the heater is often fixedly held in a suspended manner in order to absorb thermal deformation, particularly at a high temperature of 1600 ° C. or higher. It is said that it cannot be used unless it is fixed by hanging, and since it has a furnace structure in which heaters are arranged in the four side surfaces of the molded body, when firing a flat large molded product with a flat area of 800 cm ² or more, the center Temperature distribution occurs from part to end, cracks are generated due to shrinkage during sintering, or density unevenness occurs, and in order to fire large molded products, a heater is used to increase the amount of heat generated. As a result, the furnace volume is increased, the equipment cost is increased, and furthermore, there is a problem that the amount of introduced oxygen gas for suppressing the dissociation of ITO at the time of firing is high and the cost is high.
[0005]
In view of the problems in the conventional methods described above, the present invention is an improved large-sized film that is low in cost, high density over a wide area of 800 cm ² or more, and uniform density in order to obtain a stable high-quality film during sputtering. The purpose is to provide an ITO sputtering target.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have provided the present invention.
That is, the present invention provides an ITO sputtering target made of an ITO sintered body having a relative density of 90% or more on average, a variation in relative density within ± 2% of the average, and a plane area of 800 cm ² or more, , Which is composed of In ₂ O ₃ and SnO ₂ , granulated mixed powder having a SnO ₂ content of 2 to 20% by weight and a specific surface area of 15 m ² / g or more, and the resulting granulated powder was pressure-molded. Then, the plate-shaped molded body obtained was placed in a sintering electric furnace in which heaters having heat generating areas in a range larger than the plate-shaped molded body were arranged above and below the flat portion of the plate-shaped molded body with respect to the heater. And holding the ITO sputtering target obtained by sintering at 1450 to 1550 ° C., and further, an ITO sputtering target whose relative density is 45% or more, and , In ₂ O ₃ and SnO ₂ , a mixed powder having a SnO ₂ content of 2 to 20% by weight and a specific surface area of 15 m ² / g or more is granulated, and the resulting granulated powder is pressed by an isotropic pressure press. Then, the plate-shaped molded body obtained was placed in a sintering electric furnace in which heaters having heat generating areas in a range larger than the plate-shaped molded body were arranged above and below the flat portion of the plate-shaped molded body with respect to the heater. And a method of manufacturing an ITO sputtering target that is sintered at 1450 to 1550 ° C., grounds the obtained sintered body, and is bonded to a backing plate. The body provides a method for producing an ITO sputtering target having a relative density of 45% or more.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The ITO sputtering target of the present invention is produced by an ITO sintered body having a relative density of 90% or more. When the relative density of this sintered body is less than 90%, when used as a sputtering target, a blackening substance called a nodule (a lower oxide of ITO) starting from pores tends to be formed, and the sputtering rate (deposition rate) ), Etc., and the control of the film characteristics becomes difficult.
[0008]
Further, the range of variation in the relative density is preferably within 2%. If there is a density distribution with a variation exceeding 2% in the plane of the sputtering target, nodules may be partially generated or the sputtering rate may be different, and the film characteristics vary and a uniform film cannot be formed.
[0009]
The outline of the ITO sputtering target of the present invention and its manufacturing process will be described with reference to FIG. As a raw material for the ITO sintered body, indium oxide (In ₂ O ₃ ) powder and tin oxide (SnO ₂ ) powder were uniformly mixed at a predetermined ratio within the range of SnO ₂ content of 2 to 20 wt%. Use mixed powder. This content is determined in accordance with the conditions and application at the time of sputtering, but if it is less than 2% by weight, the conductivity is lowered, and if it exceeds 20% by weight, the sinterability is deteriorated.
[0010]
The specific surface area (BET value) of the powder is preferably 15 m ² / g or more as the mixed powder. If it is lower than this BET value, the sinterability is deteriorated, and firing at a high temperature of 1600 ° C. or higher is required, and the heater material, furnace material, etc. have special specifications.
Such a mixed powder is granulated prior to molding. As for granulation, spray granulation method, stirring granulation method and the like are used. Granulation is intended to improve the fluidity of the powder, and if the fluidity of the powder is not good, uneven filling occurs when the mold is filled. In particular, when the molded body is increased in size, a difference in molding density is likely to occur in the molded body. For this reason, cracks occur during molding, and cracks and uneven density of the sintered body tend to occur during firing even without molding cracks.
[0011]
The granulated powder used for molding preferably has an angle of repose of 25 ° or less, which is an index of fluidity of the granular material. Granulated powder exceeding 25 ° has poor fluidity, and it becomes difficult to uniformly fill the molding die for a sintered body having a flat area of 800 cm ² or more so that there is no uneven filling. Or cracks in the sintered body and uneven density tend to occur, and a large-sized product cannot be obtained substantially. In addition, it is desirable that the granulated powder is crushed at the time of molding to eliminate the grain boundary. From this point, granulated powder by a spray granulation method that is easily crushed is desirable.
[0012]
The granulated powder thus obtained is formed into a flat plate shape. Usually, the granulated powder is put into a mold and pressed with a uniaxial mold press to form a plate-shaped molded body. The molded plate-shaped molded body is cooled so as to obtain a more uniform molding density. A two-stage molding process in which an isostatic press such as an isostatic press is used is desirable.
That is, the granulated powder is primarily formed into a predetermined flat plate shape with a pressure of, for example, 500 kg / cm ² by a uniaxial mold press using a mold. Then, as shown in the process diagram of FIG. 1, the obtained primary molded body is put in a plastic bag or the like, sealed by a method such as a vacuum pack and waterproofed, and then subjected to an isotropic pressure press, that is, a cold static A secondary molded body having a uniform molding density is obtained by isostatic pressing in a hydraulic press. In order to obtain a sufficient molding density, it is desirable that the molding pressure at this time is sufficiently larger than the molding pressure by the uniaxial mold press and is 1,500 kg / cm ² or more.
[0013]
Further, when an ITO raw material having a SnO ₂ blending ratio of 8 to 12% by weight is used, the granulated powder having a bulk density of less than 1.3 g / cm ³ has a large number of hollow granulated powder and deformed particles. Granules having a bulk density of more than 2.0 g / cm ³ tend to have defects such as pores, and have a strong granule strength. Also, granules are likely to remain after secondary molding by cold isostatic pressing, There is a problem that density variation tends to occur in the secondary molded body.
[0014]
Sintering does not proceed unless the molding density is high to some extent. Therefore, a secondary molded body obtained by secondary molding, that is, isotropic pressing, is a sintered body having a relative density of 90% or higher after sintering. The molding density is set to a relative density of 45% or more, and preferably 50% or more so that a bonded body can be stably obtained.
[0015]
Further, the secondary molded body that has been subjected to secondary molding by an isotropic pressure press, that is, a cold isostatic press, to have a uniform molding density is fired in a sintered electric furnace. This sintering electric furnace is a batch-type heating furnace, in which heaters are vertically arranged so as to be parallel to the flat portion of the flat plate-shaped secondary molded body. In the case where the heaters are arranged on the four surfaces facing the side surface portion of the secondary molded body, a difference in density tends to occur in the flat portion of the obtained sintered body. The sintering atmosphere is an oxygen atmosphere in which oxygen gas is flowed in order to suppress dissociation of ITO.
[0016]
The sintered electric furnace A used in the embodiment will be described with reference to FIG.
The sintered electric furnace A is composed of an upper and lower split furnace body composed of a lower furnace body 1 and an upper furnace body 2 made of an alumina-based furnace material, and has a batch-type heating furnace structure in which the molded body a is converged and then the furnace is closed. The lower heater 3 and the upper heater 4 are provided. As shown in FIG. 3, the lower heater 3 has a U-shaped one-end fixing method in consideration of the thermal deformation of the heater accompanying the heat cycle, and has a 1 to 3 mm diameter mullite particle laid on the lower floor (lower furnace body) 1a. That is, it is installed on the anti-fusing material 5 and the upper heater 4 is fixed to an alumina fiber board 6 stuck to the upper wall (upper furnace body) 2a with a staple 7 made of the same material as the heater. . The lower heater 3 and the upper heater 4 are each connected to a bus bar 8 outside the furnace body 1 through terminals. In addition, the upper heater 4 and the lower heater 3 are configured so that at least the converged flat portion of the molded body a is accommodated in the heat generating area of the upper and lower heaters, and the molded body is uniformly and sufficiently heated. The lower furnace body 1 is provided with a gas inlet 9 for controlling the furnace atmosphere, and the upper furnace body 2 is provided with a thermocouple 11 for measuring the furnace temperature together with the gas outlet 10.
[0017]
Furthermore, in order not to directly apply the heat radiation from the lower heater 3 and the upper heater 4, the molded body a is uniformly heated, so that it is made of an alumina refractory for placing the molded body a on the lower floor 1 a in the furnace. After providing the leg-attached lower base plate 12 and placing the molded body a, the leg-attached upper base plate 13 covering the molded body a with an alumina refractory is placed on the leg-equipped lower base plate 12. It is.
[0018]
The dimensions of the heating portions of the upper and lower heaters 4 and 3 and the number of each heater may be determined in consideration of the dimensions of the fired molded body, the heat capacity of the furnace material, and the like. In the case of firing the controlled ITO molded body of the present invention, it has been confirmed that the upper heater 4 is suppressed from sagging due to thermal deformation and can be used repeatedly. Moreover, the lower heater 3 and the upper heater 4 can also be made into a W shape like the heater 3 'of FIG. 4 shown as another embodiment.
[0019]
In the sintered electric furnace A, the lower heater 3 is a main heat source, and the upper heater 4 is an auxiliary heat source. The material of the upper and lower heaters 4 and 3 is preferably one that can withstand the temperature holding of 1550 ° C. necessary for sintering and that can withstand the heat cycle of temperature increase and decrease from the point of use as a batch-type heating furnace. For example, molybdenum disilicide, silicon carbide, lanthanum chromite, zirconia or the like can be used, but in view of heat cycle property, molybdenum disilicide is preferable.
[0020]
Firing is held at 1450 to 1550 ° C. for 5 to 20 hours, and the atmosphere in the furnace is set to an oxygen concentration of 40% or more by introducing oxygen flow from the gas inlet 9.
In the sintering electric furnace A used in the present invention, as described above, the heater is arranged in parallel with the flat portion of the flat plate-like body to be fired a so that the upper heater 4 and the lower heater 3 are arranged, thereby causing uneven temperature ( (Sintering unevenness) can be suppressed and the furnace volume can be reduced, and the above-mentioned problems in conventional sintering furnaces have been solved.
[0021]
The sintered body obtained by firing according to the present invention is further grounded to a predetermined size and then joined to a backing plate to obtain an ITO sputtering target. The produced ITO sintered body is applied to a large sputtering target having a plane area of 800 cm ² or more, and has a relative density of 90% or more in which the occurrence of blackening of the sputtering target is suppressed during the sputtering. In addition, the density variation is as small as ± 2% of the average value, and it has the performance of maintaining a stable sputtering rate corresponding to the input power.
[0022]
In addition, the characteristic variation of the sintered body is small. For example, when the bulk specific resistance of the sintered body is measured by the four-probe method, the sintered body with a density of 98% is 1.6 × 10 ⁻⁴ Ω · cm (the variation is ± 0.1 × 10 ⁻⁴ Ω · cm). This is considered to contribute to stabilization of the discharge voltage by suppressing charge concentration during sputtering. Thus, it is considered that since the sintered body is manufactured uniformly, there is little variation in characteristics, which leads to stabilization during film formation such as stabilization of discharge voltage during sputtering and suppression of arcing.
The ITO sintered body obtained by firing of the present invention preferably has a plane area of 800 cm ² or more, has a relative density of 98% or more, and the density variation is ± 1% of the average value. Furthermore, the bulk resistance is 1.6 × 10 ⁻⁴ Ω · cm or less, the variation is very uniform within ± 0.1 × 10 ⁻⁴ Ω · cm, and the discharge voltage during sputtering is This leads to stabilization during film formation, such as stability and suppression of arcing.
[0023]
【Example】
[Example 1]
According to the steps of FIG. 1, as ITO raw material powder the weight of tin oxide (SnO ₂₎ powder and a specific surface area of 4m ² / g of indium oxide having a specific surface area of 33m ² / g by the BET method (In ₂ O ₃₎ A mixed powder was prepared by uniformly mixing the mixture at a ratio of 90:10. The specific surface area of this mixed powder was 31 m ² / g. This mixed powder was wet-dispersed with a ball mill, spray-dried, and then spray granulated to prepare a granulated granulated powder having an average particle size of 50 μm. The repose angle of this granular granulated powder was 22 °, and the bulk density was 1.5 g / cm ³ . This granular granulated powder was molded at a molding pressure of 500 kg / cm ² by a uniaxial mold press using a mold to produce a primary molded body of 400 × 510 × thickness 12 mm.
The obtained primary molded body was wrapped with a vinyl sheet, made into a waterproof pack with a vacuum pack, and then isotropically pressed at a pressure of 2000 kg / cm ² using a cold isostatic press. The relative density calculated from the external dimensions and weight of the obtained secondary molded body was 50%.
[0024]
Next, the secondary molded body is placed in the sintering electric furnace A shown in FIG. 2 in which upper and lower heaters are arranged, and the secondary molded body is disposed so that the flat portion of the secondary molded body faces the upper and lower heaters. Thus, the oxygen concentration in the furnace was maintained at 70% and sintered at a temperature of 1550 ° C. for 10 hours. The obtained sintered body had a size of about 310 × 390 × 10 mm in thickness. However, since there were waviness and warpage in the flat surface portion, a flat plate-like sintered body of 300 × 380 × 8 mm in thickness was obtained by grinding. Formed. This flat sintered body was further cut into measurement pieces each having a size of about 20 × 20 × 8 mm in thickness, and the density of each of the 285 measurement pieces was measured by the Archimedes method.
[0025]
About the flat sintered body before cutting, the relative density obtained from its external dimensions and weight was 98.11%, but the result of measuring each of the 285 measurement pieces is that the average value of the relative density is It was 98.08% (density 7.02 g / cm ³ ), the maximum value was 98.53% (density 7.05 g / cm ³ ), and the minimum value was 97.83% (density 7.00 g / cm ³ ). . That is, the variation was [average value + 0.46%] to [average value−0.25%]. Moreover, when the bulk specific resistance of each measurement piece was measured by the four-probe method, the average value was 1.6 × 10 ⁻⁴ Ω · cm, and the variation was ± 0.1 × 10 ⁻⁴ Ω · cm.
[0026]
Two flat plate-like sintered bodies obtained through the same manufacturing process using the same material as described above were each formed to a size of 300 × 350 × 8 mm by grinding. The two flat sintered bodies were aligned on the left and right sides and joined to a backing plate to obtain a target of 300 × 700 × 8 mm thickness.
When sputtering was performed using this target with a single wafer sputtering apparatus (DC magnetron sputtering apparatus), it was confirmed that sputtering was performed satisfactorily without occurrence of abnormal discharge or nodules.
[0027]
[Example 2]
The molded body produced in Example 1 was sintered in an air atmosphere introduced with outside air at 1500 ° C. for 10 hours using the sintering electric furnace A of FIG. .
The obtained sintered body was ground to obtain a plate-like sintered body having a size of 300 × 380 × 8 mm. The relative density of the flat sintered body determined from the external dimensions and weight was 91.30%.
The flat sintered body was cut into small measurement pieces having a size of about 20 × 20 × 8 mm in the same manner as in Example 1, and the density of each measurement piece was measured to obtain a relative density. The relative density obtained was 91.00% (density 6.51 g / cm ³ ) as an average value, 91.85% as a maximum value, and 89.51% as a minimum value. 9%] to [average value-1.6%].
As in Example 1, when a sputtering target was formed and sputtering was performed with the same single-wafer sputtering apparatus, nodules were slightly generated, but there was no abnormal discharge or the like, the sputtering rate was stable, and good It was confirmed that sputtering was performed.
[0028]
[Comparative example]
Sintering was performed using a compact produced in the same manner as in Example 1 and using a sintering electric furnace having another structure in which heaters were arranged on four side surfaces as a sintering furnace. The temperature conditions and oxygen concentration were the same as in Example 1. The obtained sintered body is slightly smaller in shrinkage than the sintered body in Example 1, and microcracks are generated on the side surface, and the shrinkage is smaller between the side surface and the central portion than in Example 1. There was a difference.
This sintered body was ground in the same manner as in Example 1, a small measurement piece was prepared, the density was measured, and the relative density was obtained.
The relative density is 96.2% for the flat sintered body before grinding, and the average value is 95.8% for the small measurement piece, 98.1% for the maximum value, and 93.2% for the minimum value. %, And the variation was from [average value + 2.4%] to [average value−2.7%].
When the sputtering target was formed and the sputtering was performed in the same manner as in Example 1, the generation of nodules was mostly in the portion where the density of the central portion of the sintered body was estimated to be low, and was small in the outer peripheral portion. In addition, unevenness was recognized in the plane in the target reduction method.
[0029]
Example 3
In the manufacturing method of the ITO sintered body of the present invention, a sintered body having a relative density of 94%, 96% and 99% is obtained from the ITO raw material powder of 10% SnO ₂ by controlling the molding process conditions and the like. As a comparative sample, a sintered body having a relative density of 84% was obtained. Each sintered body is ground into a disk-shaped target having a diameter of 100 mm, divided into four parts, and a single sputtering target is formed by combining the divided target pieces b, c, d, e of each sintered body as shown in FIG. Configured.
And Osamu裝this sputtering target single wafer sputtering apparatus, argon gas was introduced 29.8SCCM and oxygen gas 0.18SCCM into the apparatus, the sputtering pressure 1.6 × 10 ^-3 Torr, the discharge current 0.2 A, introduced Sputtering was performed at a power of 1.1 W / cm ² , and after consuming 8 KWH of power, the sputtering target was examined.
As shown in FIG. 5, the target pieces b, c, d, and e are noticeably blackened in the order of relative density 99% (b), 96% (c), 94% (d), and 84 (e)%. 99% of the target piece b showed almost no nodules, but 84% of the target piece e of the comparative sample produced nodules over almost the entire sputtering surface. That is, it can be seen that the target must have a relative density of at least 90%.
[0030]
Example 4
In the same manner as in Example 3, sintered bodies having a relative density of 93%, 96%, and 99% and 70% and 84% sintered bodies were obtained as comparative samples.
Sputtering targets were prepared from the respective sintered bodies, sputtered under the same processing conditions as in Example 3, the weight of the sputtering target for each predetermined integrated power amount was measured, and the etching rate by sputtering was examined.
As a result, the relationship between the accumulated power (KWH) and the weight loss (g) of the sputtering target is shown in FIG. A sputtering target having a relative density of 84% or less has a low etching rate, and a sputtering target having a relative density of 93% or more has a high etching rate and high linearity with respect to the integrated electric energy. That is, it can be seen that, as the sputtering target, the relative density is 90% or more, and when the variation exceeds the range of at least ± 2%, the difference in the etching rate becomes large.
[0031]
【The invention's effect】
As described above, according to the present invention, a large-sized and high-quality ITO sputtering target of 800 cm ² or more can be provided, and the cost, particularly the initial cost, can be suppressed by the method of the present invention. It becomes possible to stably produce a quality ITO sputtering target, and the large sputtering target can be used to industrially produce an ITO film for a large liquid crystal display.
[Brief description of the drawings]
FIG. 1 is a process diagram illustrating a method for producing a target of the present invention.
FIG. 2 is a side sectional view of a sintered electric furnace used in the present invention.
FIG. 3 is a plan sectional view taken along line III-III in FIG. 2;
FIG. 4 is a plan sectional view corresponding to FIG. 3 of a sintered electric furnace according to another embodiment.
FIG. 5 is an external view showing the state of surface blackening during sputtering of an ITO sputtering target made of sintered bodies having different densities.
FIG. 6 is a chart showing the relationship between the accumulated power amount and the weight loss during sputtering for ITO sputtering targets made of sintered bodies having different densities.
[Explanation of symbols]
A Sintered electric furnace a Molded body 1 Lower furnace body 2 Upper furnace body 3 Lower heater 4 Upper heater 5 Fusion preventing material 6 Alumina fiber board 7 Staple 8 Bus bar 9 Gas inlet 10 Gas outlet 11 Thermocouple 12 Lower base with legs Plate 13 Upper base plate with legs b, c, d, e Target piece

Claims (2)

Consists In ₂ O ₃ and SnO _2, SnO ₂ content is 2-20 wt%, a specific surface area granulated 15 m ² / g or more mixed powder, the equal Ho圧pressing the resulting granulated powder Sintering the plate-shaped body obtained by pressure molding and arranging the heaters with the heat generating area above and below the plate-shaped body, with the gas inlet at the bottom and the gas outlet at the top The flat portion of the plate-shaped molded body is held in an electric furnace so as to be parallel to the heater , and the atmosphere in the furnace is controlled by introducing gas from outside the furnace to be sintered at 1450 to 1550 ° C. A method for producing an ITO sputtering target, comprising grinding a sintered body having a plane area of 800 cm ² or more and then bonding the sintered body to a backing plate. 2. The method of manufacturing an ITO sputtering target according to claim 1, wherein the plate-like molded body has a relative density of 45% or more.

Images