JP3603693B2 - ITO sputtering target - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ITO sputtering target used in producing a transparent conductive thin film.
[0002]
[Prior art]
Indium Tin Oxide (ITO) thin films have features such as high conductivity and high transmittance, and can be easily micro-processed. Used in various fields. In particular, in the field of flat panel displays such as liquid crystal display devices, in recent years, the size and definition have been advanced, and the demand for ITO thin films as display electrodes has been rapidly increasing.
[0003]
The method of manufacturing such an ITO thin film can be roughly classified into a chemical film forming method such as a spray pyrolysis method and a CVD method, and a physical film forming method such as an electron beam evaporation method and a sputtering method. Above all, the sputtering method is used in various fields because it is a film formation method that can easily increase the area and obtain a high-performance film.
[0004]
When an ITO thin film is manufactured by a sputtering method, an alloy target composed of indium metal and tin (IT target) or a composite oxide target composed of indium oxide and tin oxide (ITO target) is used as a sputtering target. Among them, the method using an ITO target is less likely to change over time in the resistance value and transmittance of the obtained film than the method using an IT target, and the film forming conditions can be easily controlled. Has become mainstream.
[0005]
When the ITO target is continuously sputtered in a mixed gas atmosphere of an argon gas and an oxygen gas, black deposits called nodules are deposited on the surface of the target as the integrated sputtering time increases. This black deposit, which is considered to be a lower oxide of indium, precipitates around the erosion portion of the target, and is likely to cause abnormal discharge during sputtering. In addition, the deposit itself is a source of foreign matter (particles). It is known to be.
[0006]
As a result, when sputtering is performed continuously, foreign matter defects occur in the formed thin film, and this has been a cause of lowering the production yield of flat panel displays such as liquid crystal display devices. In particular, in recent years, in the field of flat panel displays, higher definition has been promoted, and such a foreign matter defect in a thin film causes an operation failure of an element, and thus has been an important problem to be solved particularly.
[0007]
In order to solve such a problem, for example, as described in Japanese Patent Application Laid-Open No. 08-060352, the generation of nodules is reduced by controlling the target density to 6.4 g / cm ³ or more and controlling the target surface roughness. It is reported that it can be done.
[0008]
However, in recent years, in order to improve the performance of a thin film formed with higher definition and higher performance of a liquid crystal display element, a film forming method of discharging with a low applied power has been adopted. . Due to the film formation with the low applied power, nodules are generated even when a target adopting the above-described method is used, which is becoming a problem. This is considered to be due to the fact that the nodule nucleus once generated does not disappear due to the strong applied power and the probability of becoming a digging remaining nucleus increases due to the decrease in the applied power.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide an ITO sputtering target that can reduce the amount of nodules generated on the target surface even when using a film forming method in which nodules are easily generated and discharge is performed at a low applied power.
[0010]
[Means for Solving the Problems]
The present inventors have conducted detailed studies on the causes of nodule formation in order to reduce the amount of nodules generated in the ITO sputtering target. As a result, in some nodules, metal indium, which is a solder material used for bonding the ITO sintered body and the backing plate, adhered to the erosion portion on the target surface during sputtering, and the adhered metal indium became a core. Discovered that the target could be dug and become a nodule. Although the cause of the metal indium serving as a nucleus for generating digging remains unclear, the metal indium attached to the target surface reacts with oxygen contained in the sputtering gas to form indium oxide. It is considered that since the resistivity is much higher than that of ITO, the material remains uncut.
[0011]
Therefore, the present inventors have conducted a detailed study on the structure of the ITO sputtering target. As a result, after the ITO sintered body and the backing plate are joined on the backing plate using indium solder, part or all of the exposed portion of the solder material is covered with an alloy composed of indium and tin, thereby causing the above problem. Can be solved, and the present invention has been completed.
[0012]
That is, the present invention relates to an ITO sputtering target in which an ITO sintered body substantially consisting of indium, tin and oxygen is bonded to a backing plate with a metal bonding agent. Covered with an alloy of indium and tin.
[0013]
Hereinafter, the present invention will be described in detail.
[0014]
The ITO sintered body used in the present invention is not particularly limited, but can be manufactured, for example, by the following method.
[0015]
First, a binder or the like is added to a mixed powder of indium oxide powder and tin oxide powder or an ITO powder or the like, and the mixture is molded by a molding method such as a press method or a casting method to produce an ITO molded body. At this time, if the average particle size of the powder used is large, the density after sintering may not be sufficiently increased, so that the average particle size of the powder used is preferably 1.5 μm or less, more preferably 0 μm or less. 0.1 to 1.5 μm. This makes it possible to obtain a sintered body having a higher sintered density.
[0016]
Further, the content of tin oxide in the mixed powder or the ITO powder is desirably 5 to 15% by weight at which the specific resistance decreases when a thin film is manufactured by a sputtering method.
[0017]
Next, a consolidation treatment such as CIP is performed on the obtained molded body as necessary. At this time, the CIP pressure is desirably ² ton / cm ² or more, preferably ² to 3 ton / cm ^{2 in} order to obtain a sufficient consolidation effect. Here, when the first molding is performed by the casting method, a binder removal treatment may be performed for the purpose of removing water and organic substances such as a binder remaining in the molded body after the CIP. Even when the initial molding is performed by a press method, it is desirable to perform the same binder removal treatment when a binder is used at the time of molding.
[0018]
The compact obtained in this way is put into a sintering furnace and sintered. As a sintering method, any method can be used, but sintering in the air is desirable in view of the cost of production equipment and the like. However, it goes without saying that other conventionally known sintering methods such as HP method, HIP method and oxygen pressure sintering method can be used.
[0019]
The sintering conditions can be appropriately selected, but the sintering temperature is desirably 1450 to 1650 ° C. in order to obtain a sufficient density increasing effect and to suppress the evaporation of tin oxide. The atmosphere during sintering is preferably air or a pure oxygen atmosphere. Also, the sintering time is desirably 5 hours or more, preferably 5 to 30 hours, in order to obtain a sufficient density increasing effect.
[0020]
In the present invention, the density of the ITO sintered body used is not particularly limited. However, in order to further suppress the occurrence of abnormal discharge and nodule due to electric field concentration at the edge of the pore of the sintered body, the relative density is 99% or more. And more preferably 99.5% or more.
[0021]
Note that the relative density (D) in the present invention indicates a relative value to the theoretical density (d) obtained from the arithmetic mean of the true densities of In ₂ O ₃ and SnO ₂ . The theoretical density determined from the arithmetic mean (d), in the sintered body composition, _{when In} 2 _{O 3} and mixtures of SnO ₂ powder (g) respectively were a, and b, _In 2 _{O 3} and SnO ₂ Using the true densities of 7.18 and 6.95 (g / cm ³ ),
d = (a + b) / ((a / 7.18) + (b / 6.95)). Then, assuming that the measured density of the sintered body is d1, the relative density D (%) is obtained by the formula: D = (d1 / d) × 100.
[0022]
Subsequently, after grinding the ITO sintered body manufactured by the above method or the like to a desired size, the sputtering surface of the ITO sintered body is mechanically polished, and the average line center roughness (Ra) of the sputtering surface is obtained. Is preferably processed to 0.8 μm or less and the maximum height (Ry) to 6.5 μm or less. More preferably, Ra is 0.1 μm or less and Ry is 2 μm or less. By doing so, it is possible to more effectively suppress the abnormal discharge generated in the uneven portion on the target surface and the formation of nodules due to the abnormal discharge. The definitions and measuring methods of Ra and Ry here are as described in JIS B0601-1994.
[0023]
The higher the density of the ITO sintered body is, the higher the hardness is, and cracks are easily generated inside the sintered body during the grinding processing. Therefore, it is desirable to perform the processing by wet processing.
[0024]
The ITO sintered body thus obtained is joined on a backing plate. The backing plate used in the present invention is not particularly limited, and examples thereof include oxygen-free copper and phosphor bronze. Further, as the metal bonding agent, indium solder or the like is preferable. This is because indium solder is soft and has a large effect of preventing cracking of the sintered body when the ITO sintered body is heated and expanded during sputtering.
[0025]
The joining may be performed, for example, in the following steps. First, the ITO sintered body and the backing plate are heated to a temperature equal to or higher than the melting point of the metal bonding agent used. Next, a bonding agent is applied to the bonded surface of the heated ITO sintered body and the backing plate. Next, after the joining surfaces of the ITO sintered body coated with the bonding agent and the backing plate are aligned with each other at a desired position on the backing plate, the target-backing plate joined body is cooled.
[0026]
The present invention is characterized in that a part or all of a bonding agent portion exposed (extruded) at the time of bonding is coated with an alloy of indium and tin, and this coating is cooled by a target-backing plate bonded body. By performing it sometimes, the operation of reheating the joined body for coating can be omitted, which is preferable.
[0027]
Specifically, when the temperature of the joined body is 1 to 5 ° C. higher than the melting point of the indium-tin alloy, the indium-tin alloy is heated to a temperature 1 to 5 ° C. higher than the melting point to expose the bonding agent. Apply and coat parts. At this time, if the indium-tin alloy is applied more than necessary, the alloy significantly protrudes from the target member, and the protruding portion is blown out by the plasma during sputtering. Therefore, it is preferable to set the thickness to 1 mm or less. Thereafter, by cooling to room temperature, the ITO target of the present invention can be obtained.
[0028]
As the indium alloy, an alloy having a composition that can provide a low resistivity as in the case of the ITO sintered body so that no digging residue occurs when an oxide is formed is suitable, and Sn / (In + Sn) is 2 to 2. 15% by weight, preferably 4 to 12% by weight is preferred.
[0029]
Sputtering is performed by adding an oxygen gas or the like as necessary to an inert gas such as argon as a sputtering gas, and controlling the gas pressure to usually 2 to 10 mTorr. As a power application method for sputtering, DC, RF, or a combination thereof can be used. However, in consideration of discharge stability, DC or RF with RF superimposed is preferable. There is no particular limitation on the power density applied to the target, but the target of the present invention is particularly effective under recent low-power discharge (2.0 W / cm ² or less) conditions.
[0030]
Further, the sputtering target according to the present invention is also effective for a target to which a third element is added for the purpose of imparting an additional function to ITO. Examples of the third element include Mg, Al, Si, Ti, Zn, Ga, Ge, Y, Zr, Nb, Hf, and Ta. The addition amount of these elements is not particularly limited. However, in order not to deteriorate the excellent electro-optical characteristics of ITO, (total sum of oxides of third element) / (total sum of oxides of ITO and third element) ) / 100 is preferably more than 0% and not more than 20% (weight ratio).
[0031]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
[0032]
Example 1
900 g of indium oxide powder having an average particle diameter of 1.3 μm and 100 g of tin oxide powder having an average particle diameter of 0.7 μm were placed in a polyethylene pot, and mixed by a dry ball mill for 72 hours to produce a mixed powder. When the tap density of the mixed powder was measured, it was 2.0 g / cm ³ .
[0033]
This mixed powder was placed in a mold and pressed at a pressure of 300 kg / cm ² to obtain a molded body. This compact was subjected to a densification treatment by CIP at a pressure of 3 ton / cm ² . Next, this compact was placed in a pure oxygen atmosphere sintering furnace and sintered under the following conditions.
[0034]
(Sintering conditions)
Sintering temperature: 1500 ° C., heating rate: 25 ° C./Hr, sintering time: 10 hours, gas introduced into the sintering furnace: oxygen, introduced gas linear velocity: 2.6 cm / min,
When the density of the obtained sintered body was measured by the Archimedes method based on JIS R1634-1998, it was 7.11 g / cm ³ (relative density: 99.4%).
[0035]
This sintered body was processed into a sintered body having a thickness of 101.6 mm × 177.8 mm and a thickness of 6 mm by wet processing, and the surface roughness of the sputtering surface of the sintered body was Ra = 0.7 μm and Ry = 5. Machined to 2 μm.
[0036]
Next, after heating the sintered body and the backing plate to 156 ° C., indium solder was applied to each joint surface. Next, the sintered body was placed at a desired position on the backing plate and then cooled to 149 ° C. Next, an indium-tin alloy containing 10% by weight of tin and heated to 149 ° C. (melting point: about 145 ° C.) was applied over the entire periphery of the exposed portion of the indium solder material on the side surface of the joint. After cooling to room temperature, an ITO target was obtained.
[0037]
This target was sputtered under the following sputtering conditions.
[0038]
DC power: 300w
Sputtering gas: Ar + O ₂
Gas pressure: 5mTorr
O ₂ / Ar: 0.1%
Under the above conditions, the sputtering test was continuously performed for 60 hours. The external appearance photograph of the target after the discharge was subjected to image processing using a computer, and the generation amount of nodules was examined. As a result, nodules were generated only in 12% of the target surface.
[0039]
Example 2
An ITO sintered body was obtained in the same manner as in Example 1. When the density of the obtained sintered body was measured, it was 7.11 g / cm ³ (relative density: 99.4%).
[0040]
This sintered body was processed into a sintered body having a thickness of 101.6 mm × 177.8 mm and a thickness of 6 mm by wet processing, and the surface roughness of the sputtering surface of the sintered body was Ra = 0.08 μm and Ry = 0. Machined to 8 μm.
[0041]
Next, after heating the sintered body and the backing plate to 156 ° C., indium solder was applied to each joint surface. Next, the sintered body was placed at a desired position on the backing plate, and then cooled to 150 ° C. Next, an indium-tin alloy containing 10% by weight of tin and heated to 150 ° C. is applied to the exposed portion over the entire periphery of the exposed portion of the indium solder material on the side surface of the joint, and then cooled to room temperature. As a result, an ITO target was obtained.
[0042]
This target was sputtered for 60 hours under the same conditions as in Example 1.
[0043]
The external appearance photograph of the target after the discharge was subjected to image processing using a computer, and the generation amount of nodules was examined. As a result, nodules were only generated in 5% of the target surface.
[0044]
Comparative Example 1
An ITO sintered body was manufactured under the same conditions as in Example 1. When the density of the obtained sintered body was measured by the Archimedes method, it was 7.11 g / cm ³ (relative density: 99.4%).
[0045]
This sintered body was processed into a sintered body having a thickness of 101.6 mm × 177.8 mm and a thickness of 6 mm by wet processing, and the surface roughness of the sputtering surface of the sintered body was Ra = 0.7 μm and Ry = 5. Machined to 2 μm.
[0046]
After heating the sintered body and the backing plate thus obtained to 156 ° C., indium solder was applied to each joint surface. Next, after placing the sintered body at a predetermined position on the backing plate, the sintered body was cooled to room temperature to obtain a target.
[0047]
This target was continuously subjected to a sputtering test for 60 hours under the same sputtering conditions as in Example 1. The external appearance photograph of the target after the discharge was subjected to image processing using a computer, and the generation amount of nodules was examined. As a result, nodules were generated on 59% of the target surface.
[0048]
【The invention's effect】
According to the present invention, generation of nodules due to metal indium used as a solder material can be prevented.

Claims (3)

In an ITO sputtering target in which an ITO sintered body substantially consisting of indium, tin, and oxygen is bonded to a backing plate with a metal bonding agent, part or all of the exposed portion of the metal bonding agent is made of indium and tin. An ITO sputtering target covered with an alloy. The ITO sputtering target according to claim 1, wherein the relative density of the ITO sintered body is 99% or more. 3. The ITO according to claim 1, wherein an average line center roughness (Ra) of a sputtering surface of the ITO sintered body is 0.8 μm or less and a maximum height (Ry) is 6.5 μm or less. Sputtering target.