WO2012108504A1

WO2012108504A1 - Oxide sintered body, and sputtering target

Info

Publication number: WO2012108504A1
Application number: PCT/JP2012/052976
Authority: WO
Inventors: 守賀金丸; 祐紀岩崎; 實松井; 後藤　裕史; 旭南部
Original assignee: 株式会社コベルコ科研
Priority date: 2011-02-10
Filing date: 2012-02-09
Publication date: 2012-08-16
Also published as: TW201245475A; JP2012180264A; JP5750064B2

Abstract

Provided is an oxide sintered body suitably used for producing an oxide semiconductor film for a display device, the oxide sintered body capable of forming an oxide semiconductor film exerting excellent conductivity, having high relative density, and exhibiting high carrier mobility. This oxide sintered body is obtained by combining and sintering a zinc oxide powder, a tin oxide powder, and an indium oxide powder. The oxide sintered body satisfies the following equation (1) when the oxide sintered body is subjected to X-ray diffraction. Equation (1): 70>[A/(A+B+C+D)]×100≥10. In equation (1), A represents the XRD peak intensity in the vicinity of 2θ=34°, B represents the XRD peak intensity in the vicinity of 2θ=31°, C represents the XRD peak intensity in the vicinity of 2θ=35°, and D represents the XRD peak intensity in the vicinity of 2θ=26.5°.

Description

Oxide sintered body and sputtering target

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

Amorphous (amorphous) oxide semiconductors used for TFTs have higher carrier mobility than general-purpose amorphous silicon (a-Si), a large optical band gap, and can be deposited at low temperatures. It is expected to be applied to next-generation displays that require high resolution and high-speed driving, and resin substrates with low heat resistance. In forming the oxide semiconductor (film), a sputtering method is preferably used in which a sputtering target made of the same material as the film is sputtered. In-plane uniformity of component composition and film thickness in the film surface direction (in the film surface) is smaller in the thin film formed by sputtering compared to thin films formed by ion plating, vacuum evaporation, and electron beam evaporation. This is because it has the advantage that a thin film having the same composition as the sputtering target can be formed. The sputtering target is usually formed by mixing and sintering oxide powder and machining.

As a composition of an oxide semiconductor used for a display device, for example, an In-containing amorphous oxide semiconductor [In—Ga—Zn—O, In—Zn—O, In—Sn—O (ITO), etc.] can be given. However, since In is used as a rare metal, there is a concern about an increase in material cost in a mass production process. Therefore, a ZTO-based oxide semiconductor that has been made amorphous by adding Sn to Zn has been proposed as an oxide semiconductor that does not contain expensive In and can reduce material costs and is suitable for mass production. No. 4 discloses a sputtering target useful for producing the ZTO-based oxide semiconductor film.

Among these, Patent Document 1 proposes a method of suppressing the occurrence of abnormal discharge and cracking during sputtering by performing long-time baking and controlling the structure so as not to contain a tin oxide phase. Patent Document 2 also suppresses abnormal discharge during sputtering by increasing the density of the ZTO-based sintered body by performing a two-step process of a low-temperature calcined powder manufacturing process at 900 to 1300 ° C. and a main baking process. A method has been proposed. Patent Document 3 proposes a method of improving the conductivity and increasing the density by including a spinel-type AB ₂ O ₄ compound. Patent Document 4 proposes a method of obtaining a dense ZTO-based sintered body by performing two steps of a low-temperature calcined powder manufacturing process at 900 to 1100 ° C. and a main baking process.

Patent Document 5 proposes a low In content ZTO-based sputtering target as a sputtering target for forming a transparent conductive film having a low specific resistance and a high relative density even if the amount of In in ITO is reduced. In general, when In in ITO is reduced, the relative density of the sputtering target is lowered and the specific resistance of the bulk is increased. However, in Patent Document 5, the bixbite structure compound represented by In ₂ O ₃ and Zn ₂ SnO ₄ are used. By allowing the represented spinel structure compound to coexist, a sputtering target that has a high density, a small specific resistance, and can suppress abnormal discharge during sputtering is realized.

JP 2007-277075 A JP 2008-63214 A JP 2010-18457 A JP 2010-37161 A JP 2007-63649 A

It is desired that a sputtering target used for manufacturing an oxide semiconductor film for a display device and an oxide sintered body that is a material thereof have excellent conductivity and a high relative density. An oxide semiconductor film obtained using the above sputtering target is desired to have high carrier mobility.

The present invention has been made in view of the above circumstances, and an object thereof is an oxide sintered body and a sputtering target that are suitably used for manufacturing an oxide semiconductor film for a display device, and have high conductivity and relative density. The object is to provide an oxide sintered body and a sputtering target that can form an oxide semiconductor film having high carrier mobility.

The oxide sintered body of the present invention that has solved the above problems is an oxide sintered body obtained by mixing and sintering zinc oxide, tin oxide, and indium oxide powders, The oxide sintered body is subjected to X-ray diffraction, the intensity of the XRD peak near 2θ = 34 ° is A, the intensity of the XRD peak near 2θ = 31 ° is B, and the intensity of the XRD peak near 2θ = 35 ° is C When the intensity of the XRD peak in the vicinity of 2θ = 26.5 ° is represented by D, it has a gist that satisfies the following formula (1).
70> [A / (A + B + C + D)] × 100 ≧ 10 (1)

In preferable embodiment of this invention, when content (atomic%) of the metal element contained in the said oxide sinter is [Zn], [Sn], and [In], respectively, following formula (2) Satisfied.
7 [In] -7 [Zn] +3 [Sn] ≦ 0 (2)

In a preferred embodiment of the present invention, the oxide sintered body has a relative density of 90% or more and a specific resistance of 1 Ω · cm or less.

Moreover, the sputtering target of the present invention that has solved the above problems is a sputtering target obtained using the oxide sintered body according to any one of the above, and has a relative density of 90% or more and a specific resistance. Has a gist where it is 1 Ω · cm or less.

According to the present invention, since the oxide sintered body and the sputtering target having a low specific resistance and a high relative density can be obtained even if the amount of In in the rare metal is reduced, the raw material cost can be greatly reduced. Further, according to the present invention, a sputtering target having excellent direct current discharge stability, excellent in-plane uniformity and film quality stability can be obtained. With the use of the sputtering target of the present invention, an oxide semiconductor film with high carrier mobility can be stably and inexpensively formed by a direct current sputtering method that facilitates high-speed film formation, so that productivity is improved.

FIG. 1 is a diagram showing a basic process for producing an oxide sintered body and a sputtering target of the present invention. FIG. 2 is a diagram showing the X-ray diffraction result of the oxide sintered body of the present invention in FIG.

The inventors of the present invention are oxide sintered bodies obtained by mixing and sintering zinc oxide, tin oxide, and indium oxide powders, and have high conductivity (low specific resistance) and high relative strength. In order to provide an oxide sintered body for a sputtering target suitable for forming an oxide semiconductor thin film having a high density and capable of applying a direct current sputtering method and having a high carrier mobility I came. As a result, the oxide sintered body was subjected to X-ray diffraction, the intensity of the XRD peak near 2θ = 34 ° was A, the intensity of the XRD peak near 2θ = 31 ° was B, and the XRD peak near 2θ = 35 ° When the intensity is expressed as C, and the intensity of the XRD peak near 2θ = 26.5 ° is expressed as D, the controlled object that satisfies the relationship of the above formula (1) achieves the intended purpose. I found it. Then, in order to obtain an oxide sintered body having such a structure, it has been found that predetermined sintering conditions (preferably sintering at a temperature of 900 to 1650 ° C. for 1 hour or more) may be performed. Completed the invention.

Further, regarding the composition of the oxide sintered body (sputtering target), a predetermined amount of In ₂ O ₃ is added to the ZTO-based oxide semiconductor oxide sintered body using ZnO and SnO ₂ as raw materials. As a result, it was found that the relative density of the oxide sintered body is improved and the specific resistance is lowered, and as a result, stable DC discharge can be continuously obtained. Further, it has been found that a TFT having an oxide semiconductor thin film formed using the above sputtering target has very high characteristics such as a carrier density of 15 cm ² / Vs or more.

Further, when the content (atomic%) of the metal element contained in the oxide sintered body is [Zn], [Sn], and [In], respectively, [Zn] + [Sn] + [In] The ratio of [In] ([In] ratio) is preferably [In] ratio = 0.01 to 0.35, and the ratio of [Zn] to [Zn] + [Sn] ([Zn] ratio) is The [Zn] ratio is preferably 0.40 to 0.95. More preferably, the [In] ratio = 0.10 to 0.30, and the [Zn] ratio = 0.50 to 0.85. In Patent Document 5 described above, in order to obtain a composition of a sputtering target suitable for film formation of a transparent conductive film, the [In] ratio is set higher than the above range, and the [Zn] ratio is set lower than the above range. The preferred composition ratio is different from the present invention that provides an oxide sintered body and a sputtering target suitable for forming an oxide semiconductor thin film.

As described above, the oxide sintered body of the present invention performs X-ray diffraction under the conditions described later, the intensity of the XRD peak near 2θ = 34 ° is A, the intensity of the XRD peak near 2θ = 31 ° is B, When the intensity of the XRD peak in the vicinity of 2θ = 35 ° is represented by C and the intensity of the XRD peak in the vicinity of 2θ = 26.5 ° is represented by D, there is a feature that satisfies the following formula (1).
70> [A / (A + B + C + D)] × 100 ≧ 10 (1)

Here, 2θ = 34 ° “neighboring” generally means that the range includes 34 ° ± 0.5 °. It is presumed that a crystal phase corresponding to Zn ₄ Sn ₂ InO _9.5 probably exists at the peak position.

Further, “the vicinity” of 2θ = 31 ° generally includes a range of 31 ° ± 1 °. It is presumed that a crystal phase corresponding to ZnSnIn _x O _{3 + 1.5X} exists at the peak position.

Moreover, 2θ = 35 ° “neighboring” means that it generally includes a range of 35 ° ± 0.4 °. It is presumed that a crystal phase corresponding to Zn _Y In ₂ O _{Y + 3} probably exists at the peak position.

Further, “2θ = 26.5 °“ near ”” generally includes a range of 26.5 ° ± 1 °. It is presumed that a crystal phase corresponding to SnO ₂ probably exists at the peak position.

The X-ray diffraction conditions in the present invention are as follows.
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 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 °

And the characteristic part of this invention exists in the place which satisfies the relationship of said Formula (1) as mentioned above. Here, satisfying the relationship of the above formula (1) (70> [A / (A + B + C + D)] × 100 ≧ 10) probably has a certain amount of crystal phase corresponding to Zn ₄ Sn ₂ InO _9.5. It is guessed that it means.

In the above formula (1), when the ratio of [A / (A + B + C + D)] × 100 is 70 or more, the sinterability is lowered and the density is not increased. Specifically, in a normal sintering method, a high density of 90% or more cannot be obtained at any temperature in the range of 900 to 1650 ° C. This is presumably because the melting point of the crystal phase corresponding to the peak of A is high, and the sinterability deteriorates in a region containing a large amount of this crystal phase. For this reason, even if it uses the obtained oxide sintered compact as a sputtering target, stable discharge cannot be performed. On the other hand, when the ratio of [A / (A + B + C + D)] × 100 is less than 10, the semiconductor characteristics of the thin film to be formed deteriorate.

Next, a preferable composition ratio (atomic ratio) of the metal elements constituting the oxide sintered body according to the present invention will be described. Hereinafter, as described above, the ratio of [In] to [Zn] + [Sn] + [In] is referred to as the [In] ratio, and the ratio of [Zn] to [Zn] + [Sn] is referred to as the [Zn] ratio.

First, the [In] ratio is preferably in the range of 0.01 to 0.35. When the [In] ratio is less than 0.01, the relative density of the oxide sintered body cannot be improved and the specific resistance cannot be reduced, and the carrier mobility of the thin film after film formation becomes low. On the other hand, if the [In] ratio exceeds 0.35, the TFT switching characteristics when a thin film is formed deteriorate. A more preferable [In] ratio is 0.10 to 0.30. A more preferable upper limit of the [In] ratio is 0.25 or less.

[Zn] ratio is preferably 0.40 to 0.95. When the [Zn] ratio is less than 0.40, the fine workability of the thin film formed by the sputtering method is lowered, and etching residues are likely to occur. A more preferable [Zn] ratio is 0.50 or more. On the other hand, when the [Zn] ratio exceeds 0.95, the chemical resistance of the thin film after film formation becomes poor, and the elution rate by acid becomes high during fine processing, so that high-precision processing cannot be performed. A more preferable [Zn] ratio is 0.85 or less. Note that the range of [Zn] ratio of approximately 0.60 to 0.82 is not preferable because the value of [A / (A + B + C + D)] × 100 tends to be 70 or more although it depends on the manufacturing conditions. It is preferable to avoid the above Zn0 ratio range of 0.60 to 0.82.

In addition, when content (atom%) of the metal element contained in oxide sinter is [Zn], [Sn], and [In], respectively, it is preferable to satisfy the following formula (2). By satisfying the following formula (2), the specific resistance is further reduced, which is preferable.
7 [In] -7 [Zn] +3 [Sn] ≦ 0 (2)

The oxide sintered body of the present invention satisfies a relative density of 90% or more and a specific resistance of 1 Ω · cm or less.

(Relative density 90% or more)
The oxide sintered body of the present invention has a very high relative density, preferably 90% or more, and more preferably 95% or more. A high relative density not only can prevent the generation of cracks and nodules during sputtering, but also provides advantages such as maintaining a stable discharge continuously to the target life.

(Specific resistance 1Ω · cm or less)
The oxide sintered body of the present invention has a small specific resistance, preferably 1 Ω · cm or less, more preferably 0.1 Ω · cm or less. Accordingly, film formation by a direct current sputtering method using plasma discharge using a direct current power source is possible, and physical vapor deposition (sputtering method) using a sputtering target can be efficiently performed on the production line of the display device.

Next, a method for producing the oxide sintered body of the present invention will be described.

The oxide sintered body of the present invention is obtained by mixing and sintering zinc oxide, tin oxide, and indium oxide powders, and the basic process from the raw material powder to the sputtering target is shown in FIG. . In FIG. 1, oxide powder is mixed, pulverized, dried, granulated, molded (molded (not shown)), sintered oxide sintered body, processed, bonded, and sputtering target formed. It shows the basic process to get. Although not shown in FIG. 1, heat treatment may be performed as necessary after sintering. Among the above steps, the present invention is characterized in that the sintering conditions are appropriately controlled as will be described in detail below, and the other steps are not particularly limited, and usually used steps can be appropriately selected. . Hereinafter, although each process is demonstrated, this invention is not the meaning limited to this.

First, zinc oxide powder, tin oxide powder, and indium 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 trace amount of impurity elements may impair the semiconductor characteristics of the oxide semiconductor film. The blending ratio of each raw material powder is preferably controlled so that the ratio of Zn, Sn, and In is within the above-described range.

Mixing and pulverization are preferably performed by using a pot 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.

Next, the mixed powder obtained in the above step is dried and granulated, and then molded. In the molding, it is preferable that the powder after drying and granulation is filled in a metal mold of a predetermined size, pre-molded by a mold press, and then molded by CIP (cold isostatic pressing) or the like. In order to increase the relative density of the sintered body, it is preferable to control the molding pressure for preforming to about 0.2 tonf / cm ² or more, and the pressure at the time of molding to about 1.2 tonf / cm ² or more. It is preferable.

Next, the molded body thus obtained is fired. In the present invention, in order to obtain a desired structure, sintering is preferably performed at a firing temperature: about 900 ° C. to 1650 ° C. and a holding time: about 1 hour or more. A higher firing temperature is preferable because the relative density of the sintered body is likely to be improved and can be processed in a short time. However, if the temperature is too high, the sintered body is easily decomposed and the relative density is lowered. More preferable sintering conditions are sintering temperature: about 1000 ° C. to 1600 ° C., holding time: about 2 hours or more. Further, pressure may be applied simultaneously with sintering using a press or the like, and the pressurizing pressure is preferably controlled to about 0.2 tonf / cm ² or more. By the sintering process, the specific resistance is reduced from, for example, about 100 Ω · cm (before the sintering process) to 0.1 Ω · cm (after the sintering).

After obtaining the oxide sintered body as described above, the sputtering target of the present invention can be obtained by processing and bonding according to a conventional method. The relative density and specific resistance of the sputtering target thus obtained are also very good, like the oxide sintered body, the preferred relative density is approximately 90% or more, and the preferred specific resistance is approximately 1Ω · cm or less.

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.

Zinc oxide powder having a purity of 99.99%, tin oxide powder having a purity of 99.99%, and indium oxide powder having a purity of 99.99% are blended in various ratios as shown in Table 1, and mixed in a nylon ball mill for 20 hours. did. Next, the mixed powder obtained in the above step is dried and granulated, pre-molded with a mold press at a molding pressure of 0.5 tonf / cm ² , and then subjected to main molding with a molding pressure of 3 tonf / cm ² by CIP. went. The molded body thus obtained was sintered at 1600 ° C.

The various oxide sintered bodies thus obtained are subjected to X-ray diffraction under the above-mentioned conditions, and the XRD peak intensities A to D are measured to construct the formula (1) [A / (A + B + C + D) ] × 100 ratio was calculated. Further, the relative density of the oxide sintered body was measured by the Archimedes method, and the specific resistance was measured by the four-terminal method.

Next, the oxide sintered body was processed into a shape of φ4 inch × 5 mmt and bonded to a backing plate to obtain a sputtering target. The sputtering target thus obtained was attached to a sputtering apparatus, and an oxide semiconductor film was formed on a glass substrate (size: 100 mm × 100 mm × 0.50 mm) by a DC (direct current) magnetron sputtering method. The sputtering conditions were a DC sputtering power of 150 W, an Ar / 0.1 volume% O ₂ atmosphere, and a pressure of 0.8 mTorr.

Using a thin film formed under the above sputtering conditions, a thin film transistor having a channel length of 10 μm and a channel width of 100 μm was manufactured, and carrier mobility was measured.

These results are summarized in Table 1. In Table 1, No. The X-ray diffraction results for 1 are shown in FIG.

From Table 1, it can be considered as follows.

First, No. 1 in Table 1 was used. 1, 4, 5, and 8 to 11 are examples of the present invention in which the ratio of [A / (A + B + C + D)] × 100 is 10 or more and less than 70, and satisfies the relationship of the formula (1) defined in the present invention. In all cases, the relative density of the sputtering target was 90% or more, the specific resistance was 1 Ω · cm or less, and the film had good characteristics. In addition, the carrier mobility of the thin films formed using these sputtering targets was as high as 15 cm ² / Vs or more.

In contrast, No. 1 in Table 1. 2, 3, 6, and 7 are examples in which the ratio of [A / (A + B + C + D)] × 100 described above is more than 70 and does not satisfy the relationship of the formula (1) defined in the present invention. The relative density of the sputtering target was less than 90%, and the specific resistance was higher than 1 Ω · cm. Therefore, when used as a sputtering target, the discharge was not stable and film formation was not possible. Also, the carrier mobility could not be measured (indicated by “−” in Table 1).

From the above experimental results, the sputtering target obtained by using the oxide sintered body that satisfies the requirements specified in the present invention and the composition ratio of the metal constituting the oxide sintered body also satisfies the preferable requirements of the present invention is It has been found to have very good properties, having a high relative density and low specific resistance. Moreover, since the thin film obtained using the said sputtering target has high carrier mobility, it turned out that it is very useful as an oxide semiconductor thin film.

Claims

An oxide sintered body obtained by mixing and sintering zinc oxide, tin oxide, and each powder of indium oxide,
X-ray diffraction of the oxide sintered body,
The intensity of the XRD peak near 2θ = 34 ° is A,
The intensity of the XRD peak near 2θ = 31 ° is B,
The intensity of the XRD peak near 2θ = 35 ° is C,
The intensity of the XRD peak near 2θ = 26.5 ° is D
An oxide sintered body characterized by satisfying the following formula (1):
70> [A / (A + B + C + D)] × 100 ≧ 10 (1)
2. The following formula (2) is satisfied when the content (atomic%) of the metal element contained in the oxide sintered body is [Zn], [Sn], and [In], respectively. The oxide sintered body according to 1.
7 [In] -7 [Zn] +3 [Sn] ≦ 0 (2)
The oxide sintered body according to claim 1 or 2, wherein the relative density is 90% or more and the specific resistance is 1 Ω · cm or less.
A sputtering target obtained by using the oxide sintered body according to any one of claims 1 to 3, wherein the relative density is 90% or more and the specific resistance is 1 Ω · cm or less.