JP2015166305A - Sintered oxide and sputtering target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered oxide in which the occurrence of crack during a bonding process can be suppressed, and a sputtering target using the sintered oxide.SOLUTION: There is provided the sintered oxide obtained by sintering: indium oxide; gallium oxide; and tin oxide, having a relative density of 90% or more, having an average crystal grain diameter of 3 μm or less of GaInSnOphase and having a ratio of less than 10% of course crystal grains having an average crystal grain diameter of 10 μm or more. When [In], [Ga], [Sn] denote the content ratio (atom %) of indium, gallium, tin per sum of the metal element contained in the sintered oxide, respectively, the sintered oxide satisfies 35 atom%≤[In]≤50 atom%, 20 atom%≤[Ga]≤35 atom%, and 20 atom%<[Sn]≤40 atom%, and the GaInSnOphase satisfies 0.02≤[GaInSnO]≤0.2.

Description

  The present invention relates to an oxide sintered body used when forming an oxide semiconductor thin film of a thin film transistor (TFT) used for a display device such as a liquid crystal display or an organic EL display by a sputtering method, and a sputtering target. About.

  An amorphous (amorphous) oxide semiconductor used for a TFT has higher carrier mobility than a general-purpose amorphous silicon (a-Si), has a large optical band gap, and can be formed at a low temperature. Therefore, it is expected to be applied to next-generation displays that require large size, high resolution, and high-speed driving, and resin substrates with low heat resistance. As an oxide semiconductor composition suitable for these applications, an In-containing amorphous oxide semiconductor has been proposed. For example, an In—Ga—Zn-based oxide semiconductor, an In—Ga—Zn—Sn-based oxide semiconductor, an In—Ga—Sn-based oxide semiconductor, and the like have attracted attention.

  In forming the oxide semiconductor thin film, a sputtering method is preferably used in which a sputtering target made of the same material as the thin film (hereinafter also referred to as “target material”) is sputtered. The sputtering target is used in a state where the oxide sintered body is bonded to the backing plate, but the oxide sintered body may break in the process of bonding the oxide sintered body to the backing plate. .

For example, Patent Document 1 discloses indium element (In) and gallium element (Ga) as oxide semiconductor films suitable for a patterning process in manufacturing a semiconductor element, and oxide sintered bodies that can form the semiconductor films. And tin element (Sn) of 0.10 ≦ In / (In + Ga + Sn) ≦ 0.60, 0.10 ≦ Ga / (In + Ga + Sn) ≦ 0.55, 0.0001 <Sn / (In + Ga + Sn) ≦ 0.60 An oxide sintered body containing Ga _3−x In _{5 + x} Sn ₂ O ₁₆ in an atomic ratio is disclosed.

Patent Document 2 includes, as a technique for reducing abnormal discharge during sputtering, indium element (In), gallium element (Ga), zinc element (Zn), and tin element (Sn), and Ga ₂ In ₆ Sn ₂ O. ₁₆ or a compound represented by (Ga, In) ₂ O ₃ and having a specific resistance of 200 m
An oxide sintered body of Ω · cm is disclosed.

  Further, Patent Document 3 uses a sputtering target and a target material that are excellent in sputtering operability such as an increase in sputtering rate, prevention of nodules, prevention of cracking, etc., and can form a transparent conductive film having a particularly low resistance on a low-temperature substrate. As the ITO sintered body to be obtained, 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 is disclosed.

JP 2011-174134 A JP 2008-280216 A Japanese Patent Laid-Open No. 05-311428

  Along with the recent improvement in performance of display devices, there is a demand for improvement and stabilization of characteristics of oxide semiconductor thin films, and there is a demand for more efficient production of display devices. In consideration of productivity and manufacturing cost, the sputtering target used for manufacturing an oxide semiconductor thin film for a display device and the oxide sintered body that is a material of the sputtering target suppress cracking of the sputtering target in the sputtering process. Needless to say, it is further required to suppress cracking of the oxide sintered body in the bonding process.

  This invention is made | formed in view of the said situation, The objective is to provide the oxide target which can suppress generation | occurrence | production of the crack at the time of bonding, and a sputtering target using this oxide target. is there.

The oxide sintered body of the present invention that has solved the above problems is an oxide sintered body obtained by sintering indium oxide, gallium oxide, and tin oxide, and the oxide sintered body. Coarse crystal grains having a relative density of 90% or more, an average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase of the oxide sintered body of 3 μm or less, and a crystal grain size of the oxide sintered body of 10 μm or more The ratio of indium, gallium and tin content (atomic%) with respect to all metal elements excluding oxygen contained in the oxide sintered body is less than 10%, respectively [In], [Ga] When [Sn] is satisfied, the following formulas (1) to (3) are satisfied, and when the oxide sintered body is X-ray diffracted, the Ga ₃ InSn ₅ O ₁₆ phase satisfies the following formula (4): There is a summary.
35 atomic% ≦ [In] ≦ 50 atomic% (1)
20 atomic% ≦ [Ga] ≦ 35 atomic% (2)
20 atomic% <[Sn] ≦ 40 atomic% (3)
0.02 ≦ [Ga ₃ InSn ₅ O ₁₆ ] ≦ 0.2 (4)
_{However, [Ga 3 InSn 5 O 16} ] = I (Ga 3 InSn 5 O 16) / (I (Ga 3 InSn 5 O 16) + I (Ga 2 In 6 Sn 2 O 16) + I (SnO 2))
In the formula, I (Ga ₃ InSn ₅ O ₁₆ ), I (Ga ₂ In ₆ Sn ₂ O ₁₆ ), and I (SnO ₂ ) are respectively Ga ₃ InSn ₅ O ₁₆ phase and Ga specified by X-ray diffraction. It is the diffraction peak intensity of ₂ In ₆ Sn ₂ O ₁₆ phase and SnO ₂ phase.

In a preferred embodiment of the present invention, when the oxide sintered body is subjected to X-ray diffraction, Ga ₂ I
The n ₆ Sn ₂ O ₁₆ phase satisfies the following formula (5).
0.8 ≦ [Ga ₂ In ₆ Sn ₂ O ₁₆ ] ≦ 0.98 (5)
_{However, [Ga 2 In 6 Sn 2} O 16] = I (Ga 2 In 6 Sn 2 O 16) / (I (Ga 3 InSn 5 O 16) + I (Ga 2 In 6 Sn 2 O 16) + I (SnO 2 )))
In the formula, I (Ga ₂ In ₆ Sn ₂ O ₁₆ ), I (Ga ₃ InSn ₅ O ₁₆ ), and I (SnO ₂ ) are respectively a Ga ₃ InSn ₅ O ₁₆ phase and a Ga specified by X-ray diffraction. It is the diffraction peak intensity of ₂ In ₆ Sn ₂ O ₁₆ phase and SnO ₂ phase.

  Moreover, the sputtering target of the present invention that has solved the above-mentioned problems is a sputtering target obtained using any of the oxide sintered bodies described above, and has a specific resistance of 1 Ω · cm or less.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the oxide sintered compact which can suppress generation | occurrence | production of the crack at the time of bonding, and the sputtering target using this oxide sintered compact.

FIG. 1 and No. 2 is a photograph showing the presence or absence of a black deposit in FIG.

  The inventors of the present invention will be described later as an oxide semiconductor thin film excellent in TFT mobility evaluated by high carrier mobility as compared with a conventional In—Ga—Zn-based oxide semiconductor thin film (IGZO). Invented and filed an In—Ga—Sn-based oxide semiconductor thin film (IGTO) having a specific ratio of metal elements.

  Of course, an oxide sintered body, which is a material of a sputtering target used for manufacturing an In—Ga—Sn-based oxide semiconductor thin film (IGTO), is subjected to oxide sintering in a bonding process in consideration of productivity and manufacturing cost. It is also important to further suppress the cracking of the bonded body, and for that purpose, it is necessary to improve the oxide sintered body.

  Accordingly, the present inventors have repeatedly studied to suppress cracking during bonding of an oxide sintered body that is a material of an In—Ga—Sn-based sputtering target suitable for forming the oxide semiconductor thin film. I came.

As a result, an oxide sintered body obtained by mixing and sintering indium oxide having a ratio of a specific metal element satisfying the following formulas (1) to (3); gallium oxide; (A) When the oxide sintered body is subjected to X-ray diffraction, a Ga ₃ InSn ₅ O ₁₆ phase, preferably Ga ₂
By controlling the proportion of the In ₆ Sn ₂ O ₁₆ phase, there is an effect of suppressing cracking of the oxide sintered body during bonding, (b) increasing the relative density of the oxide sintered body, Ga ₂ Ascertaining that the effect of suppressing cracking of the oxide sintered body can be further improved by reducing the average crystal grain size of the In ₆ Sn ₂ O ₁₆ phase and suppressing the ratio of coarse crystal grains. It came to.

  First, the structure of the oxide sintered body according to the present invention will be described in detail.

  In order to form an oxide semiconductor thin film having an excellent effect on TFT characteristics, it is necessary to appropriately control the contents of metal elements contained in the oxide sintered body.

Specifically, the ratio of the content (atomic%) of each metal element (indium, gallium, tin) to the total metal elements excluding oxygen contained in the oxide sintered body is [In], [Ga], [ When Sn is set, control is performed so as to satisfy the following formulas (1) to (3).
35 atomic% ≦ [In] ≦ 50 atomic% (1)
20 atomic% ≦ [Ga] ≦ 35 atomic% (2)
20 atomic% <[Sn] ≦ 40 atomic% (3)

  The above formula (1) defines the In ratio ([In] = In / (In + Ga + Sn)) in all metal elements. If [In] is too low, the effect of improving the relative density of the oxide sintered body and the reduction of the specific resistance of the sputtering target cannot be achieved, and the carrier mobility of the oxide semiconductor thin film after film formation also decreases. On the other hand, if [In] is too high, the number of carriers becomes too large to become a conductor, and the stability against stress decreases. Accordingly, [In] is 35 atomic% or more, preferably 37 atomic% or more, more preferably 40 atomic% or more, and 50 atomic% or less, preferably 47 atomic% or less, more preferably 45 atomic% or less. .

  The above formula (2) defines the Ga ratio ([Ga] = Ga / (In + Ga + Sn)) in all metal elements. [Ga] not only reduces oxygen deficiency and stabilizes the amorphous structure of the oxide semiconductor thin film, but also has an effect of improving stress resistance, particularly resistance to light + negative bias stress. On the other hand, when [Ga] is too high, mobility decreases. Accordingly, [Ga] is 20 atom% or more, preferably 22 atom% or more, more preferably 24 atom% or more, and 35 atom% or less, preferably 32 atom% or less, more preferably 29 atom% or less. .

  The above formula (3) defines the Sn ratio ([Sn] = Sn / (In + Ga + Sn)) in all metal elements. [Sn] has an effect of improving chemical resistance of the oxide semiconductor thin film such as wet etching. However, since the etching rate becomes slower as the chemical resistance is improved, if [Sn] is too high, the etching processability is lowered. Accordingly, [Sn] is more than 20 atomic%, preferably 23 atomic% or more, more preferably 25 atomic% or more, and 40 atomic% or less, preferably 35 atomic% or less, more preferably 31 atomic% or less. .

  In the oxide sintered body of the present invention, the metal element is composed of the above-mentioned ratios of In, Ga, and Sn, and does not contain Zn. As shown in the examples to be described later, when a thin film is formed using a conventional IGZO target containing In, Ga, and Zn, the compositional deviation between the IGZO target and the IGZO film increases, and the surface of the IGZO target This is because it has been found that a black deposit composed of Zn and O is produced. The black deposit peels off from the target surface during sputtering and becomes particles, which causes arcing and causes a serious problem in film formation.

  Here, it is considered that the main reason why the above problem occurs when an IGZO target is used is that the vapor pressure of Zn is higher than that of Ga and In. For example, when forming a thin film using a target, it is recommended to perform sputtering in an oxygen-containing inert atmosphere at a predetermined partial pressure after pre-sputtering only with an inert gas such as argon without oxygen, considering the cost. The However, when Zn is reduced during the pre-sputtering, the vapor pressure of Zn is high, so that it easily evaporates and adheres to the target surface, producing a black deposit. As a result, compositional deviation between the target and the film is caused, and the atomic ratio of Zn in the film is greatly reduced as compared with the target.

  The oxide sintered body of the present invention is preferably composed of indium oxide satisfying the above-mentioned predetermined metal element content; gallium oxide; and tin oxide, and the remainder is an oxide that is inevitably produced in production. Impurities such as objects.

Next, the Ga ₃ InSn ₅ O ₁₆ phase detected when the oxide sintered body is X-ray diffracted will be described. The Ga ₃ InSn ₅ O ₁₆ phase is an oxide formed by combining In, Ga, and Sn constituting the oxide sintered body of the present invention. The Ga ₃ InSn ₅ O ₁₆ phase has the effect of suppressing grain growth of Ga ₂ In ₆ Sn ₂ O ₁₆ and suppressing cracking due to stress during bonding in the oxide sintered body of the present invention.

In order to obtain an oxide sintered body having such an effect, the peak intensity of the Ga ₃ InSn ₅ O ₁₆ phase specified by X-ray diffraction needs to satisfy the following formula (4).
0.02 ≦ [Ga ₃ InSn ₅ O ₁₆ ] ≦ 0.2 (4)
_{However, [Ga 3 InSn 5 O 16} ] = I (Ga 3 InSn 5 O 16) / (I (Ga 3 InSn 5 O 16) + I (Ga 2 In 6 Sn 2 O 16) + I (SnO 2))
In the formula, I (Ga ₃ InSn ₅ O ₁₆ ), I (Ga ₂ In ₆ Sn ₂ O ₁₆ ), and I (SnO ₂ ) are respectively Ga ₃ InSn ₅ O ₁₆ phase and Ga specified by X-ray diffraction. It is the diffraction peak intensity of ₂ In ₆ Sn ₂ O ₁₆ phase and SnO ₂ phase. “I” means a measured value of X-ray diffraction intensity.

These compound phases are described in ICDD (International Center for Diffraction Data) cards 51-0214, 89-7011, and 41-1445 with respect to diffraction peaks obtained by X-ray diffraction of the oxide sintered body. They have crystal structures (corresponding to Ga ₃ InSn ₅ O ₁₆ phase, Ga ₂ In ₆ Sn ₂ O ₁₆ phase and SnO ₂ phase, respectively).

The present invention is characterized in that when the oxide sintered body is subjected to X-ray diffraction, a Ga ₃ InSn ₅ O ₁₆ phase is contained at a predetermined ratio. When the peak intensity ratio of the Ga ₃ InSn ₅ O ₁₆ phase ([Ga ₃ InSn ₅ O ₁₆ ]) is decreased, the effect of suppressing the grain growth of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase is weakened. There is a need. Preferably it is 0.05 or more, More preferably, it is 0.08 or more, More preferably, it is 0.1 or more. On the other hand, the upper limit is not particularly limited, but is 0.2 or less, preferably 0.18 or less, more preferably 0.16 or less, because the pinning effect is saturated and the cost is high.

Furthermore, in the present invention, when the oxide sintered body is X-ray diffracted, the Ga ₂ In ₆ Sn ₂ O ₁₆ phase preferably satisfies the following formula (5).
0.8 ≦ [Ga ₂ In ₆ Sn ₂ O ₁₆ ] ≦ 0.98 (5)
_{However, [Ga 2 In 6 Sn 2} O 16] = I (Ga 2 In 6 Sn 2 O 16) / (I (Ga 3 InSn 5 O 16) + I (Ga 2 In 6 Sn 2 O 16) + I (SnO 2 )))
In the formula, I (Ga ₂ In ₆ Sn ₂ O ₁₆ ), I (Ga ₃ InSn ₅ O ₁₆ ), and I (SnO ₂ ) are respectively a Ga ₃ InSn ₅ O ₁₆ phase and a Ga specified by X-ray diffraction. It is the diffraction peak intensity of ₂ In ₆ Sn ₂ O ₁₆ phase and SnO ₂ phase.

When the peak intensity ratio of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase ([Ga ₂ In ₆ Sn ₂ O ₁₆ ]) is reduced, the oxide sintered body is liable to crack during bonding. More preferably, it is 0.82 or more, More preferably, it is 0.84 or more. On the other hand, the upper limit is preferably as high as possible from the above viewpoint, but in consideration of the pinning effect by Ga ₃ InSn ₅ O ₁₆ , it is preferably 0.98 or less, more preferably 0.95 or less, and still more preferably 0.8. 92 or less, more preferably 0.9 or less.

  The relative density of the oxide sintered body of the present invention is 90% or more. By increasing the relative density of the oxide sintered body, the effect of suppressing cracking during bonding can be further improved. In order to obtain such an effect, the oxide sintered body of the present invention needs to have a relative density of at least 90% or more, preferably 95% or more, and more preferably 98% or more. The upper limit is not particularly limited and may be 100%, but 99% is preferable in consideration of manufacturing costs.

Further, in order to further enhance the effect of suppressing cracking during bonding, it is necessary to refine the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase of the oxide sintered body. Specifically, the fracture surface of the oxide sintered body, that is, the oxide sintered body is cut in the thickness direction at an arbitrary position, and a scanning electron microscope (SEM: Scanning Electron Microscope) is formed at an arbitrary position on the surface of the cut surface. The cracks of the oxide sintered body can be further suppressed by setting the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase to be 3 μm or less. A preferable average crystal grain size is 2.8 μm or less, more preferably 2.5 μm or less. On the other hand, the lower limit of the average crystal grain size is not particularly limited, but the preferable lower limit of the average crystal grain size is about 0.1 μm from the balance between refinement of the average crystal grain size and production cost.

  In the present invention, it is further necessary to appropriately control the particle size distribution. Specifically, coarse crystal grains having a crystal grain size of 10 μm or more cause cracking of the oxide sintered body at the time of bonding. Therefore, it is better that the coarse crystal grains are as small as possible, and the coarse crystal grains are less than 10%, more preferably 8 % Or less, more preferably 6% or less, even more preferably 4% or less, and most preferably 0%.

  Next, the suitable manufacturing method of the oxide sintered compact of this invention is demonstrated.

  The oxide sintered body of the present invention is obtained by mixing and sintering indium oxide, gallium oxide, and tin oxide. Moreover, the sputtering target of this invention can be manufactured by processing the said oxide sintered compact. Basically, oxide powder obtained by (a) mixing and grinding → (b) drying and granulation → (c) preforming → (d) degreasing → (e) atmospheric sintering A sputter target can be obtained by bonding (f) processing → (g) the bonded body. Among the above steps, the present invention is characterized in that (e) sintering conditions are appropriately controlled as will be described in detail below, and other steps are not particularly limited, and a commonly used step is appropriately selected. be able to. Hereinafter, although each process is demonstrated, this invention is not the meaning limited to this.

  First, indium oxide powder; gallium oxide powder; and tin oxide powder are mixed in a predetermined ratio, mixed and pulverized. The purity of each raw material powder used is preferably about 99.99% or more. This is because the presence of a small amount of an impurity element may impair the semiconductor characteristics of the oxide semiconductor thin film. It is preferable to control the blending ratio of each raw material powder to be within the above range.

  (A) The mixing / pulverization is preferably performed by using a ball mill or a bead mill and adding the raw material powder together with water. The balls and beads used in these steps are preferably made of materials such as nylon, alumina, zirconia, and the like. At this time, a dispersant or a binder may be mixed in order to ensure the ease of the subsequent molding process for the purpose of uniform mixing. The mixing time is preferably 2 hours or more, more preferably 10 hours or more, and further preferably 20 hours or more.

  Next, it is preferable to perform (b) drying and granulation of the mixed powder obtained in the above step using, for example, a spray dryer.

  After drying and granulation, (c) preforming is performed. In the molding, the powder after drying and granulation is filled in a mold having a predetermined size, and preformed by a mold press. Since this preforming is performed for the purpose of improving the handleability, a compact may be formed by applying a pressing force of about 49 to 98 MPa. The obtained preform is subjected to main molding by cold isostatic pressing (CIP). In order to increase the relative density of the sintered body, the pressure during the main forming is preferably controlled to 98 to 490 MPa.

  In addition, when a dispersing agent and a binder are added to mixed powder, in order to remove a dispersing agent and a binder, it is desirable to heat a molded object and to perform (d) degreasing | defatting. The heating conditions are not particularly limited as long as the purpose of degreasing can be achieved. For example, the heating conditions may be maintained at about 500 ° C. in the atmosphere for about 5 hours.

After degreasing, the molded body is set in a mold so as to obtain a desired shape, and (e) sintering is performed by atmospheric sintering. In the present invention, the molded body is heated to a sintering temperature of 1400 to 1550 ° C., and then sintered at a holding time of the temperature: 1 to 50 hours. By sintering in these temperature ranges and holding times, a compound phase that satisfies the above formulas (1) to (3) is obtained, and a Ga ₃ InSn ₅ O ₁₆ phase that satisfies the above formula (4), preferably Can obtain a sintered body having a ratio of Ga ₂ In ₆ Sn ₂ O ₁₆ phase satisfying the above formula (5) and an appropriate particle size. When the sintering temperature is low, a Ga ₃ InSn ₅ O ₁₆ phase that satisfies the above formula (4) and a Ga ₂ In ₆ Sn ₂ O ₁₆ phase that satisfies the above formula (5) cannot be generated. Further, the oxide sintered body cannot be sufficiently densified, and a desired relative density cannot be achieved. On the other hand, if the sintering temperature becomes too high, the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase and the crystal grains of the oxide sintered body become coarse, and the Ga ₂ In ₆ Sn ₂ O ₁₆ phase. It becomes impossible to control the average crystal grain size and the average crystal grain size of the crystal grains of the oxide sintered body within a predetermined range. Accordingly, the sintering temperature is preferably 1400 ° C. or higher, more preferably 1425 ° C. or higher, further preferably 1450 ° C. or higher, preferably 1550 ° C. or lower, more preferably 1525 ° C. or lower.

Further, if the holding time at the sintering temperature is too long, the crystal grains grow and become coarse, so that the average crystal grain size of the crystal grains cannot be controlled within a predetermined range. On the other hand, if the holding time is too short, the above Ga ₃ InSn ₅ O ₁₆ phase, preferably the above Ga ₂ In ₆ Sn ₂ O ₁₆ phase, cannot be formed in the above proportion or more and cannot be sufficiently densified. . Therefore, the holding time is preferably 0.1 hour or longer, more preferably 0.5 hour or longer, and preferably 5 hours or shorter.

  Moreover, in this invention, it is preferable that the average temperature increase rate to the said sintering temperature shall be 100 degrees C / hour or less after shaping | molding. When the average heating rate exceeds 100 ° C./hour, abnormal growth of crystal grains occurs, and the ratio of coarse crystal grains increases. Also, the relative density cannot be increased sufficiently. A more preferable average heating rate is 75 ° C./hour or less, and further preferably 50 ° C./hour or less. On the other hand, the lower limit of the average heating rate is not particularly limited, but is preferably 10 ° C./hour or more, more preferably 20 ° C./hour or more from the viewpoint of productivity.

Furthermore, in the present invention, it is recommended that the temperature is temporarily maintained in the process of raising the temperature to the sintering temperature at the average temperature raising rate. Specifically, it is preferable to hold in a temperature range of 1100 ° C. or higher and 1300 ° C. or lower for 1 hour or more and 10 hours or less. By maintaining the temperature in the temperature range for a predetermined time, the formation of the Ga ₃ InSn ₅ O ₁₆ phase can be promoted to form the above ratio or more. Further, by temporarily holding, growth of crystal grains of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase can be suppressed. The lower limit of the temperature (preliminary sintering temperature) when temporarily held is more preferably 1120 ° C. or higher, and further preferably 1140 ° C. or higher. The upper limit of the temperature is more preferably 1270 ° C. or less, still more preferably 1250 ° C. or less, and still more preferably 1200 ° C. or less.

  In the sintering step, the sintering atmosphere is preferably an oxygen gas atmosphere such as an air atmosphere or an atmosphere under an oxygen gas pressure. The pressure of the atmospheric gas is preferably atmospheric pressure in order to suppress evaporation of zinc oxide having a high vapor pressure. The oxide sintered body obtained as described above has a relative density of 90% or more.

  After obtaining the oxide sintered body as described above, the sputtering target of the present invention is obtained by performing (f) processing → (g) bonding by a conventional method. The processing method of oxide sinter is not specifically limited, What is necessary is just to process to the shape according to various uses by a well-known method.

  A sputtering target can be manufactured by joining the processed oxide sintered body to a backing plate with a bonding material. Although the kind of material of the backing plate is not particularly limited, pure copper or copper alloy having excellent thermal conductivity is preferable. The type of the bonding material is not particularly limited, and various known bonding materials having electrical conductivity can be used. Examples thereof include an In-based solder material and an Sn-based solder material. The bonding method is not particularly limited. For example, the oxide sintered body and the backing plate are heated and melted at a temperature at which the bonding material dissolves, for example, about 140 to 220 ° C., and the dissolved bonding material is applied to the bonding surface of the backing plate. And after bonding each bonding surface and crimping | bonding both, it should just cool.

The sputtering target obtained by using the oxide sintered body of the present invention is free from cracking due to stress generated by impact or thermal history during bonding work, and has a very good specific resistance. Is 1 Ω · cm or less, more preferably 10 ⁻¹ Ω · cm or less, and further preferably 10 ⁻² Ω · cm or less. If the sputtering target of the present invention is used, it becomes possible to form a film that further suppresses abnormal discharge during sputtering and cracking of the sputtering target material, and physical vapor deposition using the sputtering target can be efficiently performed on the production line of the display device. Can do. The obtained oxide semiconductor thin film also shows good TFT characteristics.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and may be implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all possible and are within the scope of the present invention.

Example 1
(Preparation of sputtering target)
Mass ratios and atoms shown in Table 1 for indium oxide powder (InO _1.5 ) with a purity of 99.99%, gallium oxide powder (GaO _1.5 ) with a purity of 99.99%, and tin oxide powder (SnO ₂ ) with a purity of 99.99% Blended in a ratio, water and a dispersant (ammonium polycarboxylate) were added and mixed for 24 hours in a nylon ball mill. Next, the mixed powder obtained in the above step was dried and granulated.

The powder thus obtained was preformed with a mold press under the following conditions, and then subjected to main molding with CIP at a molding pressure of 294 MPa.
(Preform conditions)
Molding pressure: 98 MPa
When the thickness is t, the compact size: φ110mm x t13mm

  The molded body thus obtained was set in a sintering furnace and sintered under the conditions shown in Table 2. The obtained oxide sintered body was machined to finish φ100 mm × t5 mm. The oxide sintered body and the Cu backing plate are heated to 180 ° C. over 20 minutes, and then the oxide sintered body is bonded to the backing plate using a bonding material (indium) to produce a sputtering target. did.

(Measurement of relative density)
The relative density is a fracture surface of the oxide sintered body, that is, the oxide sintered body is cut in the thickness direction at an arbitrary position, and an arbitrary position on the surface of the cut surface is mirror-polished, and a scanning electron microscope (SEM) The porosity was measured using The photograph was taken at 1000 times, and the area ratio occupied by the pores in a 50 μm square region was measured to obtain the porosity. The average of 20 sheets was defined as the average porosity of the sample, and [100−average porosity] was defined as the average relative density. A relative density of 90% or more was evaluated as acceptable. The results are shown in the “Relative density (%)” column of Table 4.

(Average crystal grain size of Ga ₂ In ₆ Sn ₂ O ₁₆ phase)
The average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase is determined by mirror-grinding the fracture surface of the oxide sintered body, photographing the structure at a scanning electron microscope (SEM) magnification of 400 times, and in any direction Then, a straight line having a length of 100 μm is drawn, and the total length (L) and number (N) of the lengths of the crystal grains of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase contained in the straight line are obtained. The calculated value was defined as the “average crystal grain size of Ga ₂ In ₆ Sn ₂ O ₁₆ phase on a straight line”. Similarly, 20 straight lines are created at intervals (at least 20 μm or more) at which coarse crystal grains do not overlap, and the average grain size on each straight line is calculated. Furthermore, [the sum of the average grain sizes on each straight line / 20] was determined as “average crystal grain size of Ga ₂ In ₆ Sn ₂ O ₁₆ phase”. The Ga ₂ In ₆ Sn ₂ O ₁₆ phase is identified based on constituent element ratio and X-ray diffraction data by energy dispersive X-ray spectroscopy (EDS), and Ga ₂ In ₆ Sn ₂ O The average crystal grain size of ₁₆ phases was determined. In this example, the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase was evaluated to be 3 μm or less as acceptable. The results are shown in the “Ga ₂ In ₆ Sn ₂ O ₁₆ average particle diameter (μm)” column of Table 4.

(Ratio of coarse crystal grains)
Similar to the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase, the ratio of coarse crystal grains is determined by observing the fracture surface of the oxide sintered body with an SEM and forming a straight line having a length of 100 μm in an arbitrary direction. The crystal grains having a length of 10 μm or more cut off on this straight line were defined as coarse crystal grains. The length L (sum of a plurality of the crystal grains occupied by the coarse crystal grains on the straight line) is obtained, and the value calculated from [L / 100] is calculated as the “ratio of coarse crystal grains on the straight line” ( %). Furthermore, 20 straight lines are created at intervals (at least 20 μm or more) at which coarse crystal grains do not overlap, and the ratio of coarse crystal grains on each straight line is calculated, and [the ratio of coarse crystal grains on each straight line is calculated. The value calculated from “total / 20] was defined as“ ratio of coarse crystal grains of oxide sintered body ”(%). When the ratio of coarse crystal grains of the oxide sintered body was less than 10%, it was evaluated as acceptable. The results are shown in the column “Ratio of coarse crystal grains (%)” in Table 4.

(Ga ₃ InSn ₅ O ₁₆ phase and Ga ₂ In ₆ Sn ₂ O ₁₆ phase ratio)
The ratio of the crystal phase was determined by removing the sputtering target from the backing plate after sputtering, cutting out a 10 mm square test piece, and measuring the intensity (diffraction peak) of the diffraction line by X-ray diffraction under the following conditions.
Analysis device: “X-ray diffractometer RINT-1500” manufactured by Rigaku Corporation
Analysis conditions:
Target: Cu
Monochromatic: Uses a monochrome mate (Kα)
Target output: 40kV-200mA
(Continuous firing measurement) θ / 2θ scanning Slit: Divergence 1/2 °, Scattering 1/2 °, Received light 0.15 mm
Monochromator light receiving slit: 0.6mm
Scanning speed: 2 ° / min
Sampling width: 0.02 °
Measurement angle (2θ): 5 to 90 °

About the diffraction peak obtained by this measurement, the peak of each crystal phase was identified based on the ICDD card, and the height of the diffraction peak was measured. These peaks were selected so that the diffraction intensity of the crystal phase was sufficiently high and the overlap with the peaks of other crystal phases was as small as possible. The measured values of the peak height at the designated peak of each crystal phase are I (Ga ₃ InSn ₅ O ₁₆ ), I (Ga ₂ In ₆ Sn ₂ O ₁₆ ), and I (SnO ₂ ), respectively (“I” is The peak intensity ratio of [Ga ₃ InSn ₅ O ₁₆ ] and [Ga ₂ In ₆ Sn ₂ O ₁₆ ] was determined by the following formula.
[Ga ₃ InSn ₅ O ₁₆ ] = I (Ga ₃ InSn ₅ O ₁₆ ) / ((I (Ga ₃ InSn ₅ O ₁₆ ) + I (Ga ₂ In ₆ Sn ₂ O ₁₆ ) + I (SnO ₂ ))
[Ga ₂ In ₆ Sn ₂ O ₁₆ ] = I (Ga ₂ In ₆ Sn ₂ O ₁₆ ) / (I (Ga ₃ InSn ₅ O ₁₆ ) + I (Ga ₂ In ₆ Sn ₂ O ₁₆ ) + I (SnO ₂ ))

[Ga ₃ InSn ₅ O ₁₆ ] evaluated 0.02 or more and 0.2 or less as a pass. In addition, [Ga ₂ In ₆ Sn ₂ O ₁₆ ] was evaluated as pass from 0.8 to 0.98. The results are shown in “Ga ₃ InSn ₅ O ₁₆ intensity ratio” column and “Ga ₂ In ₆ Sn ₂ O ₁₆ intensity ratio” column in Table 4.

(Breaking during bonding)
The machined oxide sintered body was heated and bonded to a backing plate, and then it was visually confirmed whether or not cracks had occurred on the surface of the oxide sintered body. When cracks exceeding 1 mm were confirmed on the surface of the oxide sintered body, it was judged that there was a “crack”. The bonding operation was performed 10 times, and a case where there was a crack even once was rejected (“Yes”), and a case where there was no crack was evaluated as “pass” (“No”). The results are shown in the “cracking during bonding” column in Table 4.

(Resistivity)
The specific resistance value was measured by a four-probe method using a resistivity meter Loresta GP (MCP-T610 type manufactured by Mitsubishi Chemical Corporation) using φ100 mm × t5 mm after machining. The specific resistance was determined to be 1 Ω · cm or less. The results are shown in the “specific resistance (Ω · cm)” column in Table 4.

  These results are also shown in Table 4. In the rightmost column of Table 4, a comprehensive evaluation column is provided, and all of the above evaluation items are OK when all are acceptable, and NG is assigned when any one is unacceptable.

  Sample No. satisfying the preferred composition and production conditions of the present invention. In Nos. 1 to 7, cracks were not generated in the target during bonding as well as during sputtering. Moreover, the relative density and specific resistance of the sputtering target thus obtained were also good.

On the other hand, Sample No. which does not satisfy the composition of the present invention. 8 to 10 and sample Nos. That do not satisfy the production conditions. In Nos. 11 to 13, cracks occurred in the sputtering target during bonding.
Therefore, in these examples, the specific resistance was measured using a sputtering target that was bonded under bonding conditions such that no cracking occurred in the sputtering target and cracks did not occur.

Sample No. 8 is an example using the steel type e of Table 1 that has a low [In] and a high [Ga] and does not satisfy the provisions of the present invention regarding the composition of the oxide sintered body. As a result, in this example, the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase was large, the ratio of coarse crystal grains was high, and the Ga ₃ InSn ₅ O ₁₆ phase was not generated. In this example, a crack occurred in the oxide sintered body during bonding.

Sample No. No. 9 is an example using the steel type f of Table 1 which has a low [Sn] and does not satisfy the provisions of the present invention regarding the composition of the oxide sintered body. As a result, in this example, the relative density is low, the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase is large, the proportion of coarse crystal grains is high, and the Ga ₃ InSn ₅ O ₁₆ phase is not generated. It was. In this example, a crack occurred in the oxide sintered body during bonding. The specific resistance was also high.

Sample No. No. 10 is an example using the steel type g of Table 1 that has a low [In] and does not satisfy the provisions of the present invention regarding the composition of the oxide sintered body. As a result, in this example, the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase was large, the ratio of coarse crystal grains was high, and the peak intensity ratio of the Ga ₃ InSn ₅ O ₁₆ phase was too high. In this example, a crack occurred in the oxide sintered body during bonding. The specific resistance was also high.

Sample No. No. 11 is an example in which the composition of the oxide sintered body used the steel type a in Table 1 that satisfies the provisions of the present invention, but the holding temperature during sintering was high. In this example, the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase was large. In this example, a crack occurred in the oxide sintered body during bonding.

Sample No. No. 12 is an example in which the composition of the oxide sintered body used the steel type a in Table 1 that satisfies the provisions of the present invention, but the holding temperature during sintering was low. In this example, the relative density was low, the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase was large, and the proportion of coarse crystal grains was high. In this example, a crack occurred in the oxide sintered body during bonding. The specific resistance was also high.

Sample No. No. 13 is an example in which the composition of the oxide sintered body used the steel type a in Table 1 that satisfies the provisions of the present invention, but the temperature was raised to the sintering temperature without temporarily holding it. In this example, the average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase was large, the proportion of coarse crystal grains was high, and the peak intensity ratio of the Ga ₃ InSn ₅ O ₁₆ phase was too low. In this example, a crack occurred in the oxide sintered body during bonding.

Example 2
In this example, compared to a conventional In-Ga-Zn oxide sintered body (IGZO), in order to demonstrate the usefulness of the In-Ga-Sn oxide sintered body (IGTO) defined in the present invention, The following experiment was conducted.

First, No. 1 in Table 4 of Example 1 described above. An oxide semiconductor thin film was formed on a glass substrate by performing pre-sputtering before the main film formation and sputtering which is the main film formation under the following conditions using one target. For reference, no. No. 1 in Table 4 above. The composition of target No. 1 (same as component No. a in Table 1) is also shown.
Sputtering equipment: “CS-200” manufactured by ULVAC, Inc.
DC (direct current) magnetron sputtering substrate temperature: room temperature (1) pre-sputtering gas pressure: 1 mTorr
Oxygen partial pressure: 100 × O ₂ / (Ar + O ₂ ) = 0% by volume
Deposition power density: 2.5 W / cm ²
Pre-sputtering time: 10 minutes (2) Main film forming gas pressure: 1 mTorr
Oxygen partial pressure: 100 × O ₂ / (Ar + O ₂ ) = 4% by volume
Deposition power density: 2.5 W / cm ²
Film thickness: 40nm

  For comparison, No. in Table 5 Using the IGZO target described in 2, an oxide semiconductor thin film was formed under the same conditions as described above. No. above. The atomic ratio of In, Ga, and Zn in the target 2 is 1: 1: 1. The manufacturing method of the IGZO target is as follows.

(Preparation of IGZO sputtering target)
Table 1 shows indium oxide powder (In ₂ O ₃ ) having a purity of 99.99%, gallium oxide powder (Ga ₂ O ₃ ) having a purity of 99.99%, and zinc oxide powder (ZnO ₂ ) having a purity of 99.99%. It mix | blended by the mass ratio and the atomic ratio, water, the dispersing agent (polycarboxylic acid ammonium), and the binder were added, and it mixed for 20 hours with the ball mill. Next, the mixed powder obtained in the above step was dried and granulated.

The powder thus obtained was preformed with a die press under the following conditions, then heated to 500 ° C. under atmospheric pressure at atmospheric pressure, and held at that temperature for 5 hours for degreasing.
(Preform conditions)
Molding pressure: 1.0 ton / cm ²
When the thickness is t, the compact size: φ110mm x t13mm

The obtained molded body was set in a graphite mold and hot pressed under the condition G shown in Table 2. At this time, N ₂ gas was introduced into the hot press furnace and sintered in an N ₂ atmosphere.

  The obtained oxide sintered body was machined to finish φ100 mm × t5 mm. After heating the oxide sintered body and the Cu backing plate to 180 ° C. over 10 minutes, the oxide sintered body is bonded to the backing plate using a bonding material (indium) to produce a sputtering target. did.

  About each oxide semiconductor thin film obtained in this way, the ratio (atomic%) of each metal element in each thin film was measured by a high frequency inductively coupled plasma (ICP) method. Table 6 lists these results.

  When the composition (atomic%) of the target shown in Table 5 and the composition atom (%) of the film shown in Table 6 are compared, No. 1 satisfying the composition of the present invention is obtained. In IGTO target No. 1, no composition deviation was observed between the target and the film.

  On the other hand, the composition of the present invention was not satisfied and no. In the IGZO target No. 2, the composition deviation between the target and the film became large. For details, see “No. 2, the Zn ratio in the target = 33.3 atomic%, the Zn ratio in the film = 26.5 atomic%, and 6.8 atomic% decreased.

  Therefore, it was proved that a film having no composition deviation from the composition of the target can be formed by using the target of the present invention.

  Furthermore, after forming each film using each of the above targets, the surface state of each target was visually observed to evaluate the presence or absence of black deposits. For reference, these photographs are shown in FIG.

  As a result, no. When the IGTO target No. 1 was used, no black deposit was observed on the target surface after film formation as shown in the left diagram of FIG. When the IGZO target No. 2 was used, black deposits were observed on the target surface after film formation as shown in the right diagram of FIG. When black deposits are present on the surface of the target in this way, there is a risk of peeling from the surface of the target during sputtering to form particles, leading to arcing. Therefore, it was proved that the use of the target of the present invention is very useful in that not only a film having no composition deviation can be formed, but also arcing during sputtering can be prevented.

Claims (3)

An oxide sintered body obtained by sintering indium oxide; gallium oxide; and tin oxide,
The relative density of the oxide sintered body is 90% or more,
The average crystal grain size of the Ga ₂ In ₆ Sn ₂ O ₁₆ phase of the oxide sintered body is 3 μm or less,
The proportion of coarse crystal grains having a crystal grain size of 10 μm or more of the oxide sintered body is less than 10%,
When the ratio (atomic%) of indium, gallium, and tin to all metal elements excluding oxygen contained in the oxide sintered body is [In], [Ga], and [Sn], respectively, While satisfying the formulas (1) to (3),
When the oxide sintered body is subjected to X-ray diffraction, the Ga ₃ InSn ₅ O ₁₆ phase satisfies the following formula (4).
35 atomic% ≦ [In] ≦ 50 atomic% (1)
20 atomic% ≦ [Ga] ≦ 35 atomic% (2)
20 atomic% <[Sn] ≦ 40 atomic% (3)
0.02 ≦ [Ga ₃ InSn ₅ O ₁₆ ] ≦ 0.2 (4)
_{However, [Ga 3 InSn 5 O 16} ] = I (Ga 3 InSn 5 O 16) / (I (Ga 3 InSn 5 O 16) + I (Ga 2 In 6 Sn 2 O 16) + I (SnO 2))
In the formula, I (Ga ₃ InSn ₅ O ₁₆ ), I (Ga ₂ In ₆ Sn ₂ O ₁₆ ), and I (SnO ₂ ) are respectively Ga ₃ InSn ₅ O ₁₆ phase and Ga specified by X-ray diffraction. It is the diffraction peak intensity of ₂ In ₆ Sn ₂ O ₁₆ phase and SnO ₂ phase. 2. The oxide sintered body according to claim 1, wherein when the oxide sintered body is subjected to X-ray diffraction, the Ga ₂ In ₆ Sn ₂ O ₁₆ phase satisfies the following formula (5).
0.8 ≦ [Ga ₂ In ₆ Sn ₂ O ₁₆ ] ≦ 0.98 (5)
_{However, [Ga 2 In 6 Sn 2} O 16] = I (Ga 2 In 6 Sn 2 O 16) / (I (Ga 3 InSn 5 O 16) + I (Ga 2 In 6 Sn 2 O 16) + I (SnO 2 )))
In the formula, I (Ga ₂ In ₆ Sn ₂ O ₁₆ ), I (Ga ₃ InSn ₅ O ₁₆ ), and I (SnO ₂ ) are respectively a Ga ₃ InSn ₅ O ₁₆ phase and a Ga specified by X-ray diffraction. It is the diffraction peak intensity of ₂ In ₆ Sn ₂ O ₁₆ phase and SnO ₂ phase.   A sputtering target obtained by using the oxide sintered body according to claim 1, wherein the specific resistance is 1 Ω · cm or less.