JP2001081551A - Ito sputtering target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sputtering target minimal in the amount of generation of nodules even in the case of a film deposition method where sputtering is performed at a low applied electrical power. SOLUTION: An ITO sintered compact consisting essentially of indium, tin and oxygen is joined to a backing plate by a metallic joining agent, such as indium solder etc., to form an ITO sputtering target. In this target, a part or the whole of the area where the metallic joining agent is exposed is coated with an alloy consisting of indium and tin. Preferred relative density of the ITO sintered compact is >=99%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ITO sputtering target used for producing a transparent conductive thin film.

[0002]

2. Description of the Related Art Indium Tin Oxide (I
TO) thin film has features such as high conductivity and high transmittance,
Further, since fine processing can be easily performed, they are used in a wide range of fields such as display electrodes for flat panel displays, window materials for solar cells, and antistatic films. 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.

The method of producing 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. Among them, the sputtering method is used in various fields because it is a film forming method that can easily increase the area and obtain a high-performance film.

When an ITO thin film is produced by a sputtering method, an alloy target (IT target) composed of metal indium and metal tin or a composite oxide target (ITO target) composed of indium oxide and tin oxide is used as a sputtering target. . Among them, the method using an ITO target has a smaller change with 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.

When an 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). Is known to be.

As a result, when sputtering is performed continuously, foreign matter defects occur in the formed thin film, and this causes a reduction in 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, high 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.

In order to solve such a problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 08-060352, the density of the target is set to 6.4 g / cm ³ or more and the surface roughness of the target is controlled to thereby reduce the nodule. It has been reported that the occurrence can be reduced.

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. It has become. 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 probability of being a nucleus of a nodule that has once been generated due to a decrease in the applied power is not extinguished by the strong applied power and becomes a remaining digging core.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ITO sputtering target capable of reducing the amount of nodules generated on a target surface even when a film forming method in which nodules are easily generated and discharge is performed at a low applied power is used. Is to provide.

[0010]

Means for Solving the Problems The present inventors have studied in detail the cause of nodule formation in order to reduce the amount of nodule generated in an 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 was used as 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 the digging residue is not yet clear, 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 is left dug.

The present inventors have conducted detailed studies on the structure of the ITO sputtering target. As a result, after bonding the ITO sintered body and the backing plate using indium solder on the backing plate,
The inventors have found that the above problem can be solved by covering a part or the whole of the exposed portion of the solder material with an alloy made of indium and tin, and completed the present invention.

That is, the present invention provides an ITO sputtering target in which an ITO sintered body substantially consisting of indium, tin, and oxygen is bonded to a backing plate by a metal bonding agent. The present invention relates to an ITO sputtering target characterized in that part or all of the target is covered with an alloy composed of indium and tin.

Hereinafter, the present invention will be described in detail.

The ITO sintered body used in the present invention is not particularly limited, but can be produced, for example, by the following method.

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 pressing 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. .1 to 1.5μ
m. This makes it possible to obtain a sintered body having a higher sintered density.

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 produced by a sputtering method.

Next, if necessary, CI
A consolidation process such as P is performed. At this time, the CIP pressure is ² ton / cm ² or more, preferably ² ton / cm ^{2 in} order to obtain a sufficient consolidation effect.
It is desirably about ³ ton / cm ² . When the initial molding is performed by a 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 the press method, it is desirable to perform the same binder removal treatment when a binder is used at the time of molding.

The compact thus obtained is put into a sintering furnace and sintered. As the sintering method, any method can be used, but sintering in air is preferable in consideration of the cost of production equipment and the like. However, in addition to this,
It goes without saying that other conventionally known sintering methods such as the HIP method and the oxygen pressure sintering method can be used.

The sintering conditions can be appropriately selected. However, in order to obtain a sufficient density increasing effect and to suppress the evaporation of tin oxide, the sintering temperature is 1450 to 1650.
C. is desirable. 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.

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.

The relative density (D) referred to in the present invention is:
The relative values to the theoretical density (d) obtained from the arithmetic mean of the true densities of In ₂ O ₃ and SnO ₂ are shown. 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 / 6.9)
5)). Then, assuming that the measured density of the sintered body is d1, the relative density D (%) is represented by the formula: D = (d1
/ D) × 100.

Subsequently, the ITO manufactured by the above method or the like is used.
After the sintered body is ground 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 0.8 μm or less and the maximum height. It is preferable to process the thickness (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 this,
It is possible to effectively suppress abnormal discharge generated in the uneven portion of the target surface and formation of nodules due to abnormal discharge. The definitions of Ra and Ry and the measuring method here are as described in JIS B0601-1994.

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 grinding. Therefore, it is desirable to perform the processing by wet processing.

The thus obtained ITO sintered body 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.

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 surface of the ITO sintered body and the backing plate to which the bonding agent has been applied is matched and arranged at a desired position on the backing plate, the target-backing plate joined body is cooled.

The present invention is characterized in that a part or all of the bonding agent portion exposed (extruded) at the time of bonding is coated with an alloy of indium and tin. By performing the cooling at the time of cooling the body, the operation of reheating the joined body for coating can be omitted, which is preferable.

More 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. Apply and cover the exposed part of the bonding agent. 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 sputtered out by plasma during sputtering, and when the spouted particles reach the substrate, they become particles and reduce the product yield. Therefore, it is desirable that the thickness be 1 mm or less. Thereafter, by cooling to room temperature, the ITO target of the present invention can be obtained.

As the indium alloy, an alloy having a composition that can obtain a low resistivity as in the case of the ITO sintered body so that no digging remains when an oxide is formed is suitable, and Sn / (In + Sn) 2 to 15% by weight, preferably 4 to 12% by weight.

The 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 pressure of the gas at 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 can be used under the conditions of recent low power discharge (2.0 W / cm ² or less).
Especially effective.

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. As the third element, for example, Mg, Al, Si, T
i, Zn, Ga, Ge, Y, Zr, Nb, Hf, Ta and the like can be exemplified. The addition amount of these elements is not particularly limited. However, in order not to deteriorate the excellent electro-optical characteristics of ITO, (the total amount of oxides of the third element)
0% at // (ITO + sum of oxides of third elements) / 100
Over 20% (weight ratio).

[0031]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

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 put 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 .

This mixed powder was placed in a mold and charged at 300 kg /
It was pressed at a pressure of 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.

(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 / h The density of the obtained sintered body was measured by the Archimedes method based on JIS R1634-1998, and found to be 7.11 g /
cm ³ (relative density: 99.4%).

This sintered body was subjected to a wet processing method to obtain 101.6.
mm × 177.8mm, processed into a 6mm thick sintered body,
Further, the surface roughness of the sputtering surface of the sintered body was Ra =
Machined to 0.7 μm, Ry = 5.2 μm.

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.) is 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.

This target was sputtered under the following sputtering conditions.

DC power: 300 w Sputter gas: Ar + O ₂ gas pressure: 5 mTorr O ₂ / Ar: 0.1% A sputtering test was continuously performed for 60 hours under the above conditions. The external appearance photograph of the target after the discharge was subjected to image processing using a computer, and the nodule generation amount was examined. As a result, nodules were only generated on 12% of the target surface.

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%).

This sintered body was subjected to a wet processing method to obtain 101.6.
mm × 177.8mm, processed into a 6mm thick sintered body,
Further, the surface roughness of the sputtering surface of the sintered body was Ra =
Machined to 0.08 μm, Ry = 0.8 μm.

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. was applied to the exposed portion over the entire periphery of the portion where the indium solder material on the side surface of the joint was exposed.
After cooling to room temperature, an ITO target was obtained.

This target was used under the same conditions as in Example 1 for 6
Sputtering was performed for 0 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 only generated on 5% of the target surface.

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%).

This sintered body was subjected to a wet processing method to obtain 101.6.
mm × 177.8mm, processed into a 6mm thick sintered body,
Further, the surface roughness of the sputtering surface of the sintered body was Ra =
Machined to 0.7 μm, Ry = 5.2 μm.

After the thus obtained sintered body and backing plate were heated 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.

A sputtering test was continuously performed on this target under the same sputtering conditions as in Example 1 for 60 hours. The external appearance photograph of the target after the discharge was subjected to image processing using a computer, and the nodule generation amount was examined.
As a result, nodules were generated on 59% of the target surface.

[0048]

According to the present invention, generation of nodules due to metal indium used as a solder material can be prevented.

Claims (3)

[Claims] 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, a part or all of a portion where the metal bonding agent is exposed is removed. An ITO sputtering target covered with an alloy of indium and tin. 2. The ITO sputtering target according to claim 1, wherein the relative density of the ITO sintered body is 99% or more. 3. The ITO sintered body according to claim 1, wherein the sputtering surface has an average line center roughness (Ra) of 0.8 μm or less and a maximum height (Ry) of 6.5 μm or less. 3. The ITO sputtering target according to 2.