JP5218032B2 - Method for producing sintered body for transparent conductive film - Google Patents

Description

  The present invention relates to a method for producing a sintered body for a transparent conductive film.

  ITO (Indium Tin Oxide) thin film has characteristics such as high conductivity and high transmittance, and can be easily finely processed. Therefore, a wide range of display electrodes for flat panel displays, window materials for solar cells, antistatic films, etc. Used in various fields.

  As a method for forming such a transparent conductive film, a sputtering method using a sputtering target is often employed because it can form a film with a uniform thickness over a large area.

  In recent years, from the viewpoint of increasing the size of a substrate on which a thin film is formed and improving the productivity of a thin film forming process, the size of a sputtering target is increasing. Further, in order to improve productivity, a cylindrical target capable of increasing the input power has attracted attention and is being used in solar cell applications.

  However, when the sputtering target is enlarged or the input power is increased, there is a problem that the sintered body for the transparent conductive film such as ITO is easily broken. Conventionally, cracks have also occurred in the firing process and bonding process in the target manufacturing process.

  As countermeasures against cracking of the ITO sintered body, in order to improve the thermal conductivity and mechanical strength of the ITO sintered body, the relative density is 85% or more and the average crystal grain size of the sintered body is 15 μm or less. A method of sintering a compact (for example, see Patent Document 2) or the like containing a binder that decomposes below the sintering start temperature of ITO (for example, see Patent Document 1) has been proposed. The method could not sufficiently prevent cracking.

  Moreover, although the main cause of the crack of the target material is the thermal stress generated by the application of the thermal shock, there has been almost no study on the thermal shock of the target material such as ITO.

Japanese Patent Laid-Open No. 07-145478 JP 05-287331 A

  Provided is a method for producing a sintered body for a transparent conductive film that is resistant to thermal shock in order to prevent cracking of a target material.

  As a result of diligent studies to solve the above problems, the sintered compact formed by granulated powder can be controlled by electromagnetic heating so that the average crystal grain size of the sintered body can be controlled to 2 μm or less. The manufacturing method of the sintered body for transparent conductive films where the maximum allowable temperature difference calculated | required by (150) is 150 degreeC or more and the crack generation rate falls significantly was discovered.

  Aspects of the present invention are as follows.

  (1) including a step of granulating the raw material powder for transparent conductive film after mixing, a step of forming the granulated powder to produce a molded body, and a step of sintering the molded body by electromagnetic wave heating A method for producing a sintered body for a transparent conductive film, wherein the sintered body has an average crystal grain size of 2 μm or less.

  (2) The method for producing a sintered body for transparent conductive film according to (1), wherein the relative density of the sintered body for transparent conductive film is 95% or more.

  (3) The method for producing a sintered body for a transparent conductive film according to (1) or (2), wherein the raw material powder for the transparent conductive film is an indium compound powder and a tin compound powder.

  (4) The manufacturing method of the sintered body for transparent conductive films as described in (1) or (2) whose raw material powder for transparent conductive films is aluminum compound powder and zinc compound powder.

  Next, this invention is demonstrated for every process.

(1) Raw material mixing step The sintered body for transparent conductive film that can be produced in the present invention is not particularly limited, and specifically, a sintered body containing indium, tin and oxygen, aluminum, zinc, and Examples thereof include a sintered body containing oxygen and a sintered body containing gallium, zinc and oxygen.

  Examples of the sintered body containing indium, tin and oxygen include a sintered body made of indium, tin and oxygen, and a sintered body obtained by adding a third element to the sintered body. . Examples of the sintered body containing aluminum, zinc and oxygen include a sintered body made of aluminum, zinc and oxygen, and a sintered body in which a third element is further added to the sintered body. Can do.

  The raw material powder is not particularly limited. For example, metal salt powder, oxide, chloride, nitrate, carbonate, etc. of the metal element constituting the sintered body can be used, but handling properties are considered. Oxide powder is then preferred.

  The purity of each raw material powder is usually 99% or higher, preferably 99.9% or higher, more preferably 99.99% or higher. This is because if the purity is low, the impurity material may affect the transparent conductive film formed by the sputtering target using the transparent conductive film sintered body of the present invention.

For example, in the case of obtaining a sintered body containing indium, tin and oxygen, the blending of these raw materials may be 4 to 20% by weight in terms of oxide, SnO ₂ / (In ₂ O ₃ + SnO ₂ ). Preferably, it is 5 to 10% by weight. When the tin content is within this range, the resistivity of the thin film obtained when the film is formed by sputtering is lowered.

Also, aluminum, the case of obtaining a zinc and oxygen comprising at sintered body is preferably from 1 to 10 wt% in _{Al 2 O 3 / (ZnO +} Al 2 O 3) in terms of oxide, more preferably 2 ~ 5% by weight. When the aluminum content is within this range, the resistivity of the thin film obtained when the film is formed by sputtering is lowered.

  The mixing of each of these powders is not particularly limited, but dry, wet media agitation type mills or medialess container rotary mixing, mechanical agitation types using balls and beads such as zirconia, alumina, nylon resin, etc. Examples of the mixing method include mixing. Specific examples include a ball mill, a bead mill, an attritor, a vibration mill, a planetary mill, a jet mill, a V-type mixer, a paddle mixer, and a twin-shaft planetary agitation mixer.

  Next, the raw material powder is granulated by spray drying or the like. The reason is that the powder at the time of filling is uniformly filled, and a homogeneous molded body is obtained. It is particularly important to obtain a homogeneous molded body in a molded body having a complicated shape such as a cylinder.

  This is because the sintered body for transparent conductive film is less susceptible to thermal shock than typical ceramic sintered bodies such as alumina and zirconia, and obtaining a sintered body with a uniform composition and structure It is important for the stability of Furthermore, in electromagnetic wave heating, self-heating due to microwave absorption of the target fired product is used, and therefore the composition of the molded body and the uniformity of the structure are very important for obtaining a uniform sintered body.

  The average particle diameter of the granulated particles is preferably 30 to 200 μm, more preferably 40 to 150 μm, and even more preferably 50 to 100 μm. Within this range, the structure of the sintered body becomes uniform and a sintered body having a high sintered density can be obtained.

  The slurry for spray drying can be adjusted by, for example, mixing raw material powder with a dispersant, an organic binder, and ion-exchanged water. Examples of the dispersant include polycarboxylic acid compounds composed of homopolymers or copolymers of acrylates and acrylates. Examples of the organic binder include a mixture of polyvinyl alcohol, acrylic acid / acrylamide copolymer, acrylic acid / methacrylic acid copolymer, and the like.

  The addition amount of the dispersant and the organic binder is preferably less than 2% by weight based on the amount of the raw material powder. Moreover, in order to improve the yield and productivity in a degreasing process, the addition amount of an organic binder and a dispersing agent may be made less than 1 weight%, or it is not necessary to add.

  The apparatus used for spray drying of the present invention is not particularly limited. Examples of the fine particle forming method include a rotating disk method, a pressure injection nozzle method, and a two-fluid nozzle method, and a drying method includes a parallel flow method, a counter flow method, and a mixing method.

  In the molding process, molding aids such as polyvinyl alcohol, acrylic polymer, methylcellulose, waxes, and oleic acid may be added to the raw material powder.

(2) Molding step The molding method is not particularly limited, and a molding method capable of molding the powder granulated in step (1) into a desired shape can be appropriately selected. Examples thereof include a press molding method, a casting molding method, and an injection molding method.

The molding pressure is not particularly limited as long as it does not cause cracks in the molded body and can be handled, but it is preferable to increase the molding density as much as possible. Therefore, it is also possible to use a method such as cold isostatic pressing (CIP) molding. In order to obtain a sufficient consolidation effect, the CIP pressure is 1 ton / cm ² or more, preferably ² ton / cm ² or more, and more preferably ² to 3 ton / cm ² .

  Here, when the first molding is performed by a casting method and then CIP is performed, a binder removal treatment may be performed for the purpose of removing moisture and organic substances such as binder remaining in the molded body after CIP. . Even when the first molding is performed by the press method, the same debinding treatment can be performed when a binder is added in the raw material mixing step.

(3) Firing step Next, the obtained molded body is put into a sintering furnace and sintered. As a sintering method, sintering by electromagnetic wave heating which can obtain a sintered body having a high density and a small average crystal grain size is performed.

  As electromagnetic waves, continuous or pulsed microwaves such as 2.45 GHz, millimeter waves such as 28 GHz, or submillimeter waves generated from a magnetron or gyrotron can be used. The electromagnetic wave frequency can be selected appropriately from the sintering behavior of the object to be fired, but a microwave of 2.45 GHz is preferable in consideration of economics such as the cost of the oscillator.

  As the electromagnetic wave firing furnace to be used, various firing furnaces such as a batch type, a continuous type, and a hybrid type with an external heating type can be used.

  In the case of firing by microwaves, the obtained molded body is placed on a setter and surrounded by a heat insulating material. At this time, it is also possible to install a material for the isothermal barrier inside the heat insulating material. As a material for the setter and the isothermal barrier, a material having heat resistance at the firing temperature of the object to be fired may be selected. For example, a material having high heat resistance such as alumina, mullite, zirconia, or SiC is selected.

  Although it does not specifically limit about a temperature increase rate, From a viewpoint of making an average crystal grain size small, it is 20-600 degreeC / hour, Preferably it is 100-600 degreeC / hour, More preferably, it is 200-500 degreeC / hour. In the case of a molded body containing moisture and binder, the moisture and binder component may volatilize because the molded body may crack if the moisture or binder component volatilizes, especially when the molded body contains a large volume. In a certain temperature range, for example, a temperature range of 100 to 400 ° C, the rate of temperature rise is preferably 20 to 100 ° C / hour.

  The setting of the maximum temperature during firing can be controlled by the material and the target average crystal grain size and density. When obtaining a sintered body containing indium, tin and oxygen, 1400 to 1650 ° C., preferably 1450 It is -1600 degreeC, More preferably, it is 1400-1550 degreeC. Moreover, when obtaining the sintered compact containing aluminum, zinc, and oxygen, it is 1100-1400 degreeC, Preferably it is 1100-1300 degreeC.

  The holding time at the maximum temperature is not particularly limited, but 10 hours or less is sufficient.

  Further, the temperature lowering rate is not particularly defined and may be appropriately determined in consideration of the capacity of the sintering furnace, the size and shape of the sintered body, the ease of cracking, and the like.

  The atmosphere during sintering is preferably in an oxygen stream when a sintered body containing indium, tin and oxygen is obtained. Moreover, when obtaining the sintered compact containing aluminum, zinc, and oxygen, the inside of air | atmosphere or inert gas is preferable. A sintered body having a high density can be obtained by firing in these atmospheres.

  Next, the sintered body for transparent conductive films manufactured by the method of the present invention will be described.

  The sintered body for transparent conductive film produced by the method of the present invention has an average crystal grain size of 2 μm or less. It is because it becomes easy to carry out fine crystallization by sintering the molded object shape | molded with granulated powder by electromagnetic wave heating. For example, in the case of a sintered body for a transparent conductive film made of indium, tin and oxygen, if the tin content is small, the average crystal grain size of the sintered body is likely to be coarsened. In addition, the average crystal grain size of the sintered body can be controlled to 2 μm or less. The average crystal grain size of the present invention is a cord diameter determined by a cord method.

  When the average crystal grain size of the sintered body is 2 μm or less, the maximum allowable temperature difference obtained by the thermal shock test according to JIS R1648 is 150 ° C. or more.

  When joining the sintered body for transparent conductive film and the backing plate, indium in a molten state is used. Since the melting point of indium solder is 156.6 ° C. and a temperature difference of about 150 ° C. can occur between the inside and outside of the sintered body, if the maximum allowable temperature difference is 150 ° C. or more, cracks during bonding are significantly reduced. It is possible.

  Further, although the surface temperature of the target material during sputtering is not known in detail, a temperature difference occurs between the part being sputtered and the part not being sputtered. In the case of a cylindrical sputtering target, since it is used at a high output and the sputtering target is rotating, the sputtering target is exposed to a high temperature during the sputtering. Continue. Therefore, cracks may occur due to repeated fatigue for a long time, but if the maximum allowable temperature difference is 150 ° C. or more, it is considered that the frequency of cracks is significantly reduced.

  The relative density of the transparent conductive film sintered body produced by the method of the present invention is preferably 95% or more, and more preferably 98% or more. This is because if it is less than 95%, the discharge stability and the quality of the sputtering thin film may be affected.

  In the present invention, the average crystal grain size of the sintered body can be controlled to 2 μm or less by sintering the molded body formed of the granulated powder by electromagnetic wave heating, and the maximum allowable temperature difference obtained by the thermal shock test. Becomes 150 ° C. or higher, and the crack generation rate is greatly reduced.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, each measurement in a present Example was performed as follows.

(1) Sintered body density It measured by the Archimedes method. In the case of a sintered body made of indium, tin and oxygen, the relative density (D) is a relative value with respect to a theoretical density ( _dITO ) obtained from an arithmetic average of true densities of In ₂ O ₃ and SnO _2. Show. The theoretical density ( _dITO ) obtained from the arithmetic mean is the true density of each of the target composition when the mixed amount of In ₂ O ₃ and SnO ₂ powder is a (g) and b (g). 18 (g / cm ³ ), 6.95 (g / cm ³ )
_dITO = (a + b) / ((a / 7.18) + (b / 6.95)) (1)
Is required. When the measured density of the sintered body is d ₁ , the relative density D is obtained by D = d ₁ / d _ITO × 100 (%).

Further, in the case of a sintered body made of aluminum, zinc, and oxygen, when the mixed amount of ZnO and Al ₂ O ₃ powder is x (g) and y (g), each true density is 5.68 (g / cm ³ ) and 3.99 (g / cm ³ )
d _AZO = (x + y) / ((x / 5.68) + (y / 3.99)) (2)
When the density of the actually obtained sintered body is d ₂ , the relative density D can be obtained by D = d ₂ / d _AZO × 100.

(2) Average crystal grain size It was determined by a code method from a scanning electron microscope (SEM) photograph. The cord length was 30 μm, and the measured crystal particles were 300 or more.

(3) Thermal shock test The temperature difference (ΔT) applied by thermal shock was 100 ° C. to 225 ° C. at 25 ° C. intervals in accordance with the thermal shock test method based on JIS R1648 relative method.
(Test conditions)
Drop height: 600mm
Cooling water tank size: 300 x 300 x 300 mm
Drop depth: 200mm
Test piece temperature measurement position: Central test piece: 4 × 3 × 40 mm
Surface roughness: 0.4 μm or less Chamfering: C surface, 0.2 mm
Number of test pieces: 5 types of residual bending test: 3-point bending test (4) Discharge evaluation A cylindrical sintered body for a target having an outer diameter of 88 mm, an inner diameter of 78 mm, and a length of 200 mm is made of titanium using indium solder. The target was bonded to the backing plate. This target was continuously discharged under the following sputtering conditions, and cracking of the target was confirmed every 20 hours, and discharge evaluation was performed up to 100 hours at the longest.
(Sputtering conditions)
Equipment: DC magnetron sputtering equipment Magnetic field strength: 500 Gauss (above target, horizontal component)
Substrate temperature: 25 ° C. (no heating)
Ultimate vacuum: 3 × 10 ⁻⁴ Pa
Sputtering gas: Ar + oxygen sputtering gas pressure: 0.5 Pa
DC power: 300W
Gas pressure: 7.0 mTorr
Oxygen gas concentration (O _{2 /} Ar): 0.05%
Example 1
Commercially available indium oxide powder (average particle size 0.8 μm) and commercially available tin oxide powder (average particle size 0.6 μm) were weighed so that SnO ₂ / (In ₂ O ₃ / SnO ₂ ) = 10 wt% Then, together with ion-exchanged water and a polycarboxylic acid-based dispersant, the mixture was pulverized and mixed with zirconia beads (0.3 mmφ) using a bead mill to form a slurry. This slurry was spray-dried with a spray dryer under the following conditions to obtain a granulated powder having an average particle size of 38 μm, a bulk density of 1.5 g / cm ³ , and a tap density of 1.7 g / cm ³ .
(Drying conditions)
Disk rotation speed: 15000 rpm
Air inlet temperature: 200 ° C
Air outlet temperature: 120 ° C
Slurry supply amount: 2.5 kg / hr
This mixed powder was put in a mold so as to obtain a cylindrical sintered body, and was treated with CIP at a pressure of ² ton / cm ² . Next, this compact was placed on a setter made of SiC in a microwave firing furnace (frequency = 2.45 GHz) and sintered under the following conditions.
(Sintering conditions)
Firing temperature: 1450 ° C
Temperature increase rate: 300 ° C./hour Temperature decrease rate: 100 ° C./hour Holding time at 1450 ° C .: 2 hours Atmosphere: Pure oxygen gas introduction About the obtained sintered body, the sintered body density, average crystal grain size, thermal shock Evaluation of test and discharge evaluation was carried out. The results are shown in Table 1.

(Example 2)
The same slurry as in Example 1 was changed to the following drying conditions, and spray-dried with a spray dryer. The average particle size was 50 μm, the bulk density was 1.6 g / cm ³ , and the tap density was 1.8 g / cm ³ . A granulated powder was obtained. Firing was performed in the same manner as in Example 1 except that the pressure at CIP was 1.5 ton / cm ² and the firing temperature was 1550 ° C. About the obtained sintered compact, the sintered compact density, the average crystal grain diameter, the thermal shock test, and evaluation of discharge evaluation were implemented. The results are shown in Table 1.
(Drying conditions)
Disk rotation speed: 12000 rpm
Air inlet temperature: 200 ° C
Air outlet temperature: 100 ° C
Slurry supply amount: 2.5 kg / hr
(Example 3)
Firing was performed in the same manner as in Example 1 except that the content of tin oxide was SnO ₂ / (In ₂ O ₃ + SnO ₂ ) = 5 wt%. About the obtained sintered compact, the sintered compact density, the average crystal grain diameter, the thermal shock test, and evaluation of discharge evaluation were implemented.

Example 4
Commercially available zinc oxide powder (average particle size 0.9 μm) and commercially available aluminum oxide powder (average particle size 0.3 μm) were weighed so that Al ₂ O ₃ / (ZnO + Al ₂ O ₃ ) = 2 wt%. Along with ion-exchanged water and a polycarboxylic acid-based dispersant, the mixture was pulverized with alumina beads (0.3 mmφ) using a bead mill, mixed, and slurried. This slurry was spray-dried with a spray dryer under the following conditions to obtain a granulated powder having an average particle size of 70 μm, a bulk density of 1.5 g / cm ³ , and a tap density of 1.8 g / cm ³ .
(Drying conditions)
Disk rotation speed: 10000rpm
Air inlet temperature: 200 ° C
Air outlet temperature: 110 ° C
Slurry supply amount: 3.0 kg / hr
This mixed powder was put into a mold so as to obtain a sintered body having a predetermined shape, and was subjected to treatment by CIP at a pressure of ² ton / cm ² . Next, this molded body was placed in a microwave set furnace (frequency = 2.45 GHz) on a SiC setter with an alumina plate having a thickness of 2 mm, placed thereon, and sintered under the following conditions.
(Sintering conditions)
Firing temperature: 1300 ° C
Temperature increase rate: 300 ° C./hour Temperature decrease rate: 100 ° C./hour Holding time at 1300 ° C .: 1 hour Atmosphere: Pure nitrogen gas introduction About the obtained sintered body, the sintered body density, average crystal grain size, thermal shock Evaluation of test and discharge evaluation was carried out. The results are shown in Table 1.

(Comparative Example 1)
Example 1 except that an electric furnace (heating element = molybdenum silicite heater) was used and the firing temperature = 1600 ° C., the heating rate = 50 ° C./hour, and the holding time at 1600 ° C. = 5 hours. Firing was performed. About the obtained sintered compact, the sintered compact density, the average crystal grain diameter, the thermal shock test, and evaluation of discharge evaluation were implemented. The results are shown in Table 1.

(Comparative Example 2)
The same as in Example 4 except that an electric furnace (heating element = molybdenum silicite heater) was used and the firing temperature = 1400 ° C., the heating rate = 50 ° C./hour, and the holding time at 1400 ° C. = 4 hours. Firing was performed. About the obtained sintered compact, the sintered compact density, the average crystal grain diameter, the thermal shock test, and evaluation of discharge evaluation were implemented. The results are shown in Table 1.
(Comparative Example 3)
Commercially available indium oxide powder (average particle size 0.8 μm) and commercially available tin oxide powder (average particle size 0.6 μm) were weighed so that SnO ₂ / (In ₂ O ₃ / SnO ₂ ) = 5 wt%. The mixture was then placed in a polyethylene pot and mixed for 16 hours by a dry ball mill to prepare a mixed powder. The bulk density of the mixed powder was measured and found to be 1.7 g / cm ³ .

  Using this mixed powder, firing was performed in the same manner as in Example 2. About the obtained sintered compact, the sintered compact density, the average crystal grain diameter, the thermal shock test, and evaluation of discharge evaluation were implemented. The results are shown in Table 1.

Claims (4)

A step of mixing and granulating without adding an organic binder so as to have an average particle diameter of 30 to 200 μm after mixing the raw material powder for the transparent conductive film, and forming the granulated powder to produce a molded body And a method for producing a sintered body for a transparent conductive film, wherein the sintered body has an average crystal grain size of 2 μm or less. The method for producing a sintered body for a transparent conductive film according to claim 1, wherein the relative density of the sintered body for the transparent conductive film is 95% or more. The method for producing a sintered body for a transparent conductive film according to claim 1 or 2, wherein the raw material powder for the transparent conductive film is an indium compound powder and a tin compound powder. The method for producing a sintered body for a transparent conductive film according to claim 1 or 2, wherein the raw material powder for the transparent conductive film is an aluminum compound powder and a zinc compound powder.