JP5437919B2 - ITO sputtering target and manufacturing method thereof - Google Patents

Description

The present invention relates to an ITO sputtering target. More specifically, the present invention relates to an ITO sputtering target that hardly causes cracking during bonding even when the SnO ₂ content is 5% by mass or less.

ITO (Indium-Tin-Oxide) films are widely used for transparent electrodes and touch panels of flat panel displays because of their high permeability and electrical conductivity. The ITO film for transparent electrodes usually contains about 10% by mass of Sn in terms of SnO ₂ , but the ITO film for touch panels is required to have a relatively high resistance, so the content of Sn However, an ITO film of about 3% by mass in terms of SnO ₂ is used. The ITO film is generally formed by sputtering an ITO sputtering target. The ITO sputtering target is generally used by being bonded to a Cu backing plate. For this reason, when forming an ITO film for a touch panel, sputtering is generally performed by bonding an ITO sputtering target having a Sn content of about 3 mass% in terms of SnO ₂ to a Cu backing plate.

However, it is known that an ITO sputtering target having a small Sn content, for example, an ITO sputtering target having a Sn content of 5% by mass or less in terms of SnO ₂ is brittle and easily cracked. In particular, it is known that an ITO sputtering target having a Sn content of 5% by mass or less in terms of SnO ₂ is likely to crack when bonded to a backing plate made of Cu or the like.

  As a technique for preventing the cracking of the ITO sputtering target, for example, in Japanese Patent Laid-Open No. 9-125236, it is composed of In, O and 0.1 mass% or more of Sn, the relative density is 90% or more, and the residual stress x is An indium oxide-based sintered body in which −200 ≦ x ≦ 200 MPa is disclosed. In this document, if the sintered body has a large residual stress x that deviates from the range of −200 ≦ x ≦ 200 MPa, it is not preferable because the sintered body is cracked or cracked.

JP-A-6-316760 discloses an ITO porous sintered body obtained by molding and sintering a powder composed of 1 to 20% by weight of a tin oxide component and the remainder of an indium oxide component. An ITO porous sintered body obtained by calcining at 1200 to 1600 ° C., ball milling the powder after calcining, granulating and forming, and sintering at 900 to 1100 ° C. is disclosed. . In JP-A-6-64959, the sintering density is 90% or more and 100% or less, the sintered particle diameter is 1 μm or more and 20 μm or less, and the amount of (In0.6Sn0.4) ₂ O ₃ is 10% or less. An ITO sintered body is disclosed. Japanese Patent Application Laid-Open No. 5-31428 discloses a high-density ITO sintered body having a sintered density of 90% to 100% and a sintered particle diameter of 1 μm to 20 μm.

However, in any of these ITO sintered bodies, when the Sn content is 5% by mass or less in terms of SnO ₂ , cracking cannot be sufficiently prevented, particularly when bonding to a backing plate. It was difficult to prevent cracks that occurred in the film.

Japanese Patent Laid-Open No. 9-125236 JP-A-6-316760 JP-A-6-64959 JP-A-5-311428

  An object of the present invention is to provide an ITO sputtering target in which cracking is unlikely to occur even when the Sn content is small, and in particular, cracking is unlikely to occur when bonding to a backing plate.

  As a result of intensive research to achieve the above object, the present inventor has found that when a specific amount of compressive residual stress is applied to an ITO sputtering target, cracking is unlikely to occur even if the Sn content is reduced, and particularly the backing. It has been found that cracks are less likely to occur when bonding to a plate, and the present invention has been completed.

That is, the present invention for achieving the above object is an ITO sputtering target having a Sn content of 5% by mass or less in terms of SnO ₂ , wherein the residual stress is −650 to −200 MPa. It is.

As a preferable aspect of this ITO sputtering target,
The Sn content is 4% by mass or less in terms of SnO ₂ ,
The Sn content is 1 to 4% by mass in terms of SnO ₂ .

The ITO sputtering target is
When the ITO sputtering target is used by being bonded to a backing plate made of a metal material having a thermal expansion coefficient of 2.386 × 10 ⁻⁵ / ° C. or less, the residual stress may be −600 to −200 MPa. Preferably
In the case of an ITO sputtering target used by being bonded to a backing plate made of a metal material having a thermal expansion coefficient of greater than 2.386 × 10 ⁻⁵ / ° C., the residual stress is preferably −650 to −250 MPa. .

  In another invention, the raw material powder for producing the ITO sputtering target is sintered in a sintering furnace at a sintering temperature of 1450 to 1700 ° C., and the obtained ITO sintered body is sintered at the temperature in the sintering furnace. The method of manufacturing the ITO sputtering target, wherein the temperature is lowered from 700 to 900 ° C. at a rate of 300 ° C./h or more and then cooled at a rate of 10 to 100 ° C./h.

The ITO sputtering target of the present invention hardly breaks even when the Sn content is 5% by mass or less in terms of SnO ₂ , and does not easily crack even when bonding to a Cu backing plate or the like. According to the method for producing an ITO sputtering target of the present invention, the ITO sputtering target can be produced efficiently.

The ITO sputtering target according to the present invention is characterized in that the Sn content is 5% by mass or less in terms of SnO ₂ and the residual stress is −650 to −200 MPa. Hereinafter, the ITO sputtering target according to the present invention will be described in detail.

  The ITO sputtering target according to the present invention has a residual stress of −650 to −200 MPa. The residual stress becomes a tensile residual stress when the numerical value is positive, and becomes a compressive residual stress when the numerical value is negative. Therefore, the ITO sputtering target of the present invention has a compressive residual stress.

In the present invention, the residual stress was measured using an X-ray diffraction method which is a general method for measuring residual stress. Specifically, using panalical X'Pert PRO, X-ray tube: Cu target, diffraction angle: 2θ = 30.6 ° (In ₂ O ₃ (222)), measurement method: ψ0 side tilt method, The measurement was performed under the measurement conditions of an elastic constant: 178 GPa and a Poisson's ratio: 0.33.

Since the ITO sputtering target of the present invention has a residual stress in the above range, it is difficult to crack even if the Sn content is 5% by mass or less in terms of SnO ₂ , and particularly difficult to crack when bonding to a backing plate. .

  This is considered to be due to the following reasons. The backing plate is usually made of Cu. When bonding the sputtering target and the backing plate, the sputtering target and the backing plate are heated to about 200 ° C., a bonding agent is applied to the bonding surfaces of the sputtering target and the backing plate, and the bonding surfaces are bonded together. Crimp the. Thereafter, the sputtering is completed by cooling the sputtering target and the backing plate. During this cooling, both the sputtering target and the backing plate shrink, but Cu or the like, which is the material of the backing plate, has a larger thermal expansion coefficient than ITO, and therefore the backing plate shrinks more than the sputtering target. That is, a sputtering target having a shrinkage rate smaller than that of the backing plate can shrink only a length shorter than the length of shrinking of the backing plate in the direction parallel to the bonding surface. For this reason, the above-described cooling causes the sputtering target to warp so that the center part is lifted upward (on the opposite side to the side where the backing plate is located), and is pulled to the upper surface (surface opposite to the bonding surface) part of the sputtering target. The stress of this will arise. Ceramics such as ITO are generally strong in compressive force but weak in tensile force. For this reason, it becomes easy to produce a crack in an ITO sputtering target by the tensile stress added at the time of cooling. At this time, if the ITO sputtering target of the present invention has a compressive residual stress as described above, even if a tensile stress is applied by cooling, the tensile stress is canceled by the compressive residual stress of the sputtering target. As a result, cracking is difficult to occur.

  If the residual stress of the sputtering target is −200 MPa or less (the compressive residual stress of the sputtering target is equal to or greater than the compressive residual stress corresponding to −200 MPa), a sufficient buffering force against the tensile stress can be obtained. The cracking of the sputtering target can be sufficiently prevented. However, if the residual stress is smaller than −650 MPa (the compressive residual stress of the sputtering target is larger than the compressive residual stress corresponding to −650 MPa), the sputtering target cannot withstand the compressive residual stress, and at the end of firing or This is not preferable because cracks are likely to occur during processing. On the other hand, if the residual stress of the sputtering target is larger than −200 MPa (the compressive residual stress of the sputtering target is smaller than the compressive residual stress corresponding to −200 MPa), sufficient buffering force against the tensile stress cannot be obtained. Therefore, it is not possible to sufficiently prevent the sputtering target from cracking. Therefore, for example, a sintered body having a residual stress x described in JP-A-9-125236 with −200 ≦ x ≦ 200 MPa does not have a compressive residual stress sufficient to cancel the tensile stress described above. On the contrary, since it has a tensile residual stress, cracking is likely to occur during bonding to the backing plate.

  As described above, it is considered that the cracking of the sputtering target during bonding is caused by the difference in thermal expansion coefficient between the sputtering target and the backing plate. Since the thermal expansion coefficient differs depending on the type of backing plate material, the difference in thermal expansion coefficient between the sputtering target and the backing plate also differs depending on the type of backing plate material. The sputtering target is easily broken. For this reason, in order to surely prevent the sputtering target from cracking during bonding, the residual stress of the ITO sputtering target is reduced (the compressive residual stress is increased) as the thermal expansion coefficient of the metal material forming the backing plate is increased. It is desirable.

Specifically, when the thermal expansion coefficient of the metal material forming the backing plate is larger than 2.386 × 10 ⁻⁵ / ° C., the residual stress of the ITO sputtering target bonded to the backing plate is −650 to − The pressure is preferably 250 MPa, more preferably −500 to −300 MPa, and the optimum value is around −400 MPa. Therefore, for example, when an Al backing plate is used, the residual stress of the ITO sputtering target is preferably within the above range.

On the other hand, when the thermal expansion coefficient of the metal material forming the backing plate is 2.386 × 10 ⁻⁵ / ° C. or less, the residual stress of the ITO sputtering target bonded to the backing plate is −600 to −200 MPa. It is preferable that there is, more preferably −450 to −250 MPa, and an optimum value is around −350 MPa. Therefore, for example, when using a backing plate made of Cu, stainless steel, Ni alloy and Ti alloy, the residual stress of the ITO sputtering target is preferably within the above range.
In addition, in this invention, the numerical value of a thermal expansion coefficient is based on a chemical dictionary (reduced edition, Kyoritsu Publishing Co., Ltd. (1984)).

The ITO sputtering target according to the present invention contains Sn in an amount of more than 0 mass% and 5 mass% or less in terms of SnO ₂ , preferably more than 0 mass% and 4 mass%, more preferably 1 to 4 mass%. contains. If the Sn content exceeds 5% by mass in terms of SnO ₂ , the strength of the sputtering target will increase, and cracking will not easily occur even when subjected to the above tensile stress from the backing plate during cooling of the bonding. There is little need to control the residual stress. If the Sn content is 5% by mass or less in terms of SnO ₂ , the strength of the sputtering target is low, and cracking is likely to occur when subjected to the tensile stress, so there is a need to control the residual stress of the sputtering target. Large cracking can be prevented by making the residual stress within the above range. When the Sn content is 4% by mass or less in terms of SnO ₂ , cracking is particularly likely to occur when the tensile stress is applied. Therefore, there is a great need to control the residual stress of the sputtering target, and the residual stress is The effect of preventing cracking when it is within the range is great. Moreover, it is especially preferable that the content of Sn is 1 to 4% by mass in terms of SnO _{2 because} the residual stress of the sputtering target can be easily within the above range.

  The shape and size of the ITO sputtering target according to the present invention is not particularly limited, and any shape and size of the sputtering target can effectively generate cracks if the residual stress is within the above range. Can be prevented. However, the greater the area of the surface parallel to the bonding surface of the sputtering target, the greater the warping force during cooling and the greater the tensile stress. Therefore, the larger the compressive residual stress of the sputtering target, the less likely it is to crack. In addition, the smaller the thickness of the sputtering target, the more likely it is warped during cooling and the greater the tensile stress, so the larger the compressive residual stress the sputtering target has, the more difficult it is to crack. Therefore, the larger the area of the surface parallel to the bonding surface of the sputtering target, or the smaller the thickness of the sputtering target, the smaller the residual stress of the sputtering target within the above range (higher compressive residual stress).

  The relative density of the ITO sputtering target according to the present invention is preferably 95% or more, and more preferably 97% or more. When the relative density is 95% or more, cracking hardly occurs, arcing and particle generation can be suppressed during sputtering, and good sputtering becomes possible.

  Although there is no restriction | limiting in particular in the manufacturing method of the ITO sputtering target which concerns on this invention, When sintering the obtained sintered compact after sintering an ITO molded object, it is constant from sintering temperature. There can be mentioned a method of rapidly cooling to the above temperature and gradually cooling from that temperature to room temperature. In this method, compressive residual stress is generated in the sputtering target by quenching in a high temperature range. On the other hand, in the low temperature range, a temperature difference between the sputtering target and the outside air tends to occur at the time of cooling. Therefore, if the quenching is performed in the same manner as in the high temperature range, the sputtering target is cracked by the thermal stress generated due to the temperature difference. Since it is easy, slow cooling is performed to prevent cracking. Hereinafter, this method will be described in detail.

A mixed powder is prepared by mixing In ₂ O ₃ powder and SnO ₂ powder, which are raw material powders, so that the content of SnO ₂ powder is 5% by mass or less. The specific surface area of the In ₂ O ₃ powder measured by the BET (Brunauer-Emmett-Teller) method is usually 1 to 40 m ² / g, and the specific surface area of the SnO ₂ powder measured by the BET method is usually 1 to 40 m ² / g. It is. The specific surface area of the mixed powder measured by the BET method is usually 1 to 40 m ² / g.

In addition, instead of In ₂ O ₃ powder and SnO ₂ powder, ITO powder having a Sn content of 5% by mass or less in terms of SnO ₂ may be used as the raw material powder. ITO powder and In ₂ O ₃ powder, ITO powder and SnO ₂ powder, or ITO powder, In ₂ O ₃ powder and SnO ₂ powder may be mixed and used so that the Sn content is 5% by mass or less in terms of SnO ₂ .

There is no restriction | limiting in particular in a mixing method, For example, it can put in a pot and it can carry out by ball mill mixing.
The mixed powder can be molded as it is to form a molded body, which can be sintered. However, if necessary, the mixed powder can be molded by adding a binder to form a molded body. As this binder, the binder used when obtaining a molded object in a well-known powder metallurgy method, for example, polyvinyl alcohol etc., can be used. Moreover, you may degrease the obtained molded object by the method employ | adopted in a well-known powder metallurgy method as needed. As the molding method, a method employed in a known powder metallurgy method, for example, cast molding can be applied. The density of the molded body is usually 50 to 75%.

  The obtained molded body is sintered to obtain a sintered body. The sintering furnace used for sintering is not particularly limited as long as the cooling rate can be controlled during cooling, and may be a sintering furnace generally used for powder metallurgy. There is no restriction | limiting in particular as sintering atmosphere, It can be set as air atmosphere.

  The rate of temperature increase is usually 100 to 500 ° C./h from the viewpoint of increasing the density and preventing cracking. The sintering temperature is usually 1450 to 1700 ° C, preferably 1500 to 1600 ° C, and the holding time at the sintering temperature is usually 3 to 30 hours, preferably 5 to 10 hours. When the sintering temperature and the holding time are within the above ranges, a high-density sintered body can be obtained.

  After the sintering is completed, the temperature in the sintering furnace is lowered at a high speed from the sintering temperature to 700 to 900 ° C., preferably to 750 to 850 ° C., more preferably around 800 ° C. That is, the sintered body is rapidly cooled in this temperature range. By rapidly cooling the sintered body within this temperature range, residual stress can be applied to the sintered body, and even if the sintered body is rapidly cooled in such a high temperature range, the sintered body is not cracked. It is unlikely to occur. The temperature lowering rate in this temperature range is 300 ° C./h or more, preferably 300 to 900 ° C./h, more preferably 400 to 800 ° C./h, and further preferably 500 to 700 ° C./h. If the rate of temperature decrease is less than 300 ° C./h, it is difficult to reliably apply the residual stress in the above range to the sputtering target. In addition, the larger the temperature decrease rate, the greater the residual stress can be applied to the sputtering target. However, if the temperature decrease rate is too large, the heater cannot withstand rapid cooling and easily deteriorates, so the temperature decrease rate is 900 ° C./h or less. Preferably there is.

  Thereafter, the temperature in the sintering furnace is lowered at a low speed, for example, to room temperature. That is, the sintered body is gradually cooled in this temperature range. By slowly cooling the sintered body within this temperature range, cracking of the sintered body can be prevented as described above. The temperature lowering rate in this temperature range is 10 to 100 ° C./h, preferably 10 to 50 ° C./h, more preferably 10 to 30 ° C./h. When cooling is performed at such a temperature lowering rate, the sintered body can be reliably prevented from cracking and the production efficiency is not impaired.

  There is no particular limitation on the method for adjusting the temperature drop rate. The temperature can be lowered at a high speed, for example, by turning off the heater of the sintering furnace or blowing a cooling gas into the furnace. The temperature can be lowered at a low speed, for example, by controlling the temperature of the heater of the sintering furnace.

The ITO sintered body thus obtained can be cut into a desired shape as necessary and ground to obtain an ITO sputtering target.
The ITO sputtering target of the present invention is usually used by bonding to a backing plate. The backing plate is usually made of Cu, Al or stainless steel. As the bonding agent, a bonding agent used for bonding a conventional ITO sputtering target, for example, In metal can be used. The bonding method is the same as the conventional ITO sputtering target bonding method. For example, the ITO sputtering target and the backing plate of the present invention are heated to a temperature at which the bonding agent melts, for example, about 200 ° C., the bonding agent is applied to the bonding surfaces of the sputtering target and the backing plate, and the bonding surfaces are attached. The two are pressed together and then cooled. Alternatively, a bonding agent is applied to the bonding surfaces of the ITO sputtering target and the backing plate of the present invention, the bonding surfaces are bonded together, and the sputtering target and the backing plate are melted at a temperature at which the bonding agent melts, for example, about 200 ° C. Cool after heating. As described above, the ITO sputtering target of the present invention is much less likely to crack during the bonding than the conventional ITO sputtering target.

[Examples 1 to 12, Comparative Examples 1 to 6]
The In ₂ O ₃ powder and SnO ₂ powder whose specific surface area measured by the BET method is the value shown in Table 1 were mixed using a ball mill so that the SnO ₂ content would be the amount shown in Table 1. A mixed powder was prepared. Table 1 shows the specific surface area of the obtained mixed powder measured by the BET method.

6% by mass of polyvinyl alcohol diluted to 4% by mass with respect to the mixed powder was added to the mixed powder, and the polyvinyl alcohol was well adapted to the powder using a mortar and passed through a 5.5 mesh sieve. The obtained powder was filled in a press mold and molded at a press pressure of 1 t / cm ² for 60 seconds to obtain a molded body of 200 mm × 500 mm × 10 mm.

The obtained molded body was put into a sintering furnace having a capacity of about 1 m ³ , oxygen was flowed into the furnace at 1 L / h, the firing atmosphere was an oxygen flow atmosphere, the heating rate was 350 ° C./h, the sintering temperature Was sintered at 1550 ° C. and the holding time at the sintering temperature was 9 h.

Thereafter, the obtained sintered body was cooled under the cooling conditions shown in Table 1.
The temperature drop rate is adjusted by turning off the heater of the sintering furnace and blowing cooling gas into the furnace when the temperature is lowered at a high speed, and when the temperature is lowered at a low speed (30 ° C./h). Was performed by controlling the temperature of the heater of the sintering furnace.

As described above, an ITO sputtering target of 176 mm × 440 mm × 8.8 mm was obtained.
The following evaluation was performed on this ITO sputtering target. The results are shown in Table 1.

<Relative density>
The relative density of the sputtering target was measured based on the Archimedes method. Specifically, the air weight of the sputtering target is divided by the volume (= the weight of the sputtering target sintered body in water / the water specific gravity at the measurement temperature), and the theoretical density ρ (g / cm ³ ) based on the following formula (X) The percentage value was defined as the relative density (unit:%).

（式（Ｘ）中、Ｃ₁〜Ｃ_iはそれぞれターゲット焼結体の構成物質の含有量（重量％）を
示し、ρ₁〜ρ_iはＣ₁〜Ｃ_iに対応する各構成物質の密度（ｇ/ｃｍ³）を示す。）。

(In the formula (X), C _{1 to} C _i indicate the content (% by weight) of the constituent material of the target sintered body, and ρ _{1 to} ρ _i are the densities of the constituent materials corresponding to C _{1 to} C _i. (G / cm ³ ).

Specifically, the [rho theoretical density (true density or calculated density), the [rho _i as ^{7.179g / cm 3, 6.95g / cm} 3 with SnO ₂ in an In ₂ O _3, a sintered body of each composition Calculated. For example, the theoretical density [rho, a 1% SnO ₂ In 7.177g / cm ^3, in ^{_{3% SnO 2 7.172g / cm 3}} , 5% SnO 2 In 7.167g / cm ^3.

<Evaluation of residual stress>
The residual stress of the obtained ITO sputtering target was measured using X-ray tube: Cu target, diffraction angle: 2θ = 30.6 ° (In ₂ O ₃ (222)), using a panoramic X'Pert PRO : Ψ0 side tilt method, elastic constant: 178 GPa, Poisson's ratio: 0.33.

<Evaluation of cracks generated during bonding to backing plate>
The cracks were evaluated using Cu backing plates (dimensions: 190 mm × 440 mm × 6 mm) for the ITO sputtering targets obtained in Examples 1 to 6, and obtained in Examples 7 to 12. For the ITO sputtering target, an Al backing plate (dimensions: 190 mm × 440 mm × 6 mm) is used, and for the ITO sputtering target obtained in Comparative Examples 1 to 6, the Cu backing plate and the above This was performed using both Al backing plates.

In was primed on the bonding surfaces of the backing plate and the ITO sputtering target, and the ITO sputtering target and the backing plate were bonded so that the bonding surfaces were in close contact with each other. After raising the temperature to 200 ° C. at which In melts, the ITO sputtering target and the backing plate were bonded by cooling to room temperature (cooling). Whether or not the bonded ITO sputtering target was cracked was observed with the naked eye, and the crack was evaluated according to the following criteria.
○: No crack was observed ×: Crack was observed

表１より、Ｃｕ製およびＡｌ製のいずれのバッキングプレートの場合にも、ＳｎＯ₂含有量が同じであっても、残留応力が−２００ＭＰａより大きいＩＴＯスパッタリングターゲットにはボンディング時に割れが発生し、残留応力が−２００〜−６５０ＭＰａの範囲のＩＴＯスパッタリングターゲットにはボンディング時に割れが発生しなかった。このように、本発明のＩＴＯスパッタリングターゲットは、Ｓｎの含有量がＳｎＯ₂換算で５質量％以下であっても、Ｃｕ製およびＡｌ製のバッキングプレート等にボンディングするときに割れが発生しにくいことが確認された。

According to Table 1, in both cases of Cu and Al backing plates, even if the SnO ₂ content is the same, an ITO sputtering target having a residual stress of greater than −200 MPa is cracked during bonding and remains. The ITO sputtering target having a stress in the range of −200 to −650 MPa did not crack during bonding. As described above, the ITO sputtering target of the present invention is less susceptible to cracking when bonded to a Cu or Al backing plate or the like, even if the Sn content is 5% by mass or less in terms of SnO _2. Was confirmed.

Claims (6)

An ITO sputtering target having a Sn content of 5% by mass or less in terms of SnO _{2 and} having a residual stress of −650 to −200 MPa. The ITO sputtering target according to claim 1, wherein the Sn content is 4% by mass or less in terms of SnO ₂ . The ITO sputtering target according to claim 1, wherein the Sn content is 1 to 4% by mass in terms of SnO ₂ . An ITO sputtering target used by being bonded to a backing plate made of a metal material having a thermal expansion coefficient of 2.386 × 10 ⁻⁵ / ° C. or less, wherein the residual stress is −600 to −200 MPa. The ITO sputtering target according to any one of claims 1 to 3. An ITO sputtering target used by being bonded to a backing plate made of a metal material having a thermal expansion coefficient larger than 2.386 × 10 ⁻⁵ / ° C., and having a residual stress of −650 to −250 MPa. The ITO sputtering target in any one of Claims 1-3.   The raw material powder for producing the ITO sputtering target was sintered in a sintering furnace at a sintering temperature of 1450 to 1700 ° C., and the obtained ITO sintered body was subjected to a temperature in the sintering furnace of 700 to 900 from the sintering temperature. 6. The production of an ITO sputtering target according to claim 1, wherein cooling is performed by lowering to 300 ° C. at a rate of 300 ° C./h or more and then lowering at a rate of 10 to 100 ° C./h. Method.