Oxide sputtering target and method for manufacturing same

Abstract

The present disclosure addresses the problem of providing: an oxide sputtering target that contains niobium, tin, and oxygen and has a low volume resistivity and a high relative density; and a method for manufacturing same. The oxide sputtering target contains niobium (Nb), tin (Sn), and oxygen (O), contains Nb in an atomic ratio of Nb / (Nb+Sn) of 0.01-0.2, has a relative density of 99.5% or more, and has a volume resistivity of 100 Ω·cm or less.

Description

Oxide sputtering target and method for producing the same

[0001] The present disclosure relates to oxide sputtering targets and methods for producing the same.

[0002] Tin oxide (SnO ２ ) thin films have excellent properties, such as high conductivity and high transmittance in the visible light region, and are therefore widely used as transparent conductive films. For example, SnO thin films are widely used as transparent electrodes for plasma displays, liquid crystal displays, organic EL displays, touch panels, solar cells, etc. ２ In recent years, thin films mainly composed of SnO ２ Attempts have also been made to use the thin film in semiconductor devices that take advantage of its n-type semiconductor properties.

[0003] SnO ２ The thin film is usually SnO ２ The film is formed using a sputtering target whose main component is argon ions. Sputtering is a type of physical vapor deposition (PVD) technique in which a sputtering target placed opposite a substrate is bombarded with argon ions at high speed, causing atoms ejected from the target to deposit on the substrate. Usually, a thin film with the same composition as the sputtering target is formed.

[0004] SnO ２ Regarding the sputtering target of the above, the following prior art is known. For example, Patent Document 1 discloses a SnO ２ Patent Document 2 discloses a sintered body (a material for forming a thin film). ２ Patent Literature 3 discloses a sintered body of Nb ２ O ５ and Ta ２ O ５ SnO containing ２ A sputtering target is disclosed.

[0005] Furthermore, Patent Document 4 discloses a tin oxide sputtering target containing one or more of tantalum, niobium, and tungsten as a dopant. Patent Document 5 discloses a tin oxide sintered body containing a cation dopant (one or more of tantalum, antimony, and niobium) and an anion dopant (one or more of fluorine and chlorine). These documents disclose the formation of a thin film using the sputtering target.

[0006] JP 2000-273622 A JP 2000-281431 A JP 2007-131891 A JP 2013-173658 A JP 2019-142761 A

[0007] As mentioned above, tin oxide (SnO ２ However, when a tin oxide sputtering target containing only niobium added thereto is produced by air sintering, the volume resistivity increases, and there is a problem that DC (direct current) sputtering, which enables high-speed film formation, cannot be stably performed (Patent Documents 1 to 3).

[0008] On the other hand, sputtering targets with low volume resistivity can be obtained by sintering using a hot pressing (HP) method or a hot isostatic pressing (HIP) method, but since sintering is performed in a vacuum or an inert atmosphere, the tin oxide is reduced, making it impossible to produce a high-density sintered body (sputtering target) (Patent Documents 4 and 5). If the relative density of a sputtering target is low, there is a problem in that particles are likely to be generated during sputtering.

[0009] In view of the above problems, an object of the present disclosure is to provide an oxide sputtering target that contains niobium, tin, and oxygen and has a low volume resistivity and a high relative density, and a method for producing the same.

[0010] In order to solve the above problems, the present inventors have conducted extensive research and have found that by appropriately controlling the sintering conditions, an oxide sputtering target having a low volume resistivity and a high relative density can be obtained.

[0011] [1] An oxide sputtering target containing niobium (Nb), tin (Sn), and oxygen (O), wherein the Nb content is 0.01 or more and 0.2 or less in atomic ratio of Nb / (Nb + Sn), the relative density is 99.5% or more, and the volume resistivity is 100 Ω cm or less. [2] The oxide sputtering target according to [1] above, wherein the coefficient of variation of the volume resistivity on the sputtering surface of the sputtering target is 0.25 or less. [3] The oxide sputtering target according to [1] above, wherein the coefficient of variation of the volume resistivity on the sputtering surface of the sputtering target is 0.20 or less. [4] The oxide sputtering target according to [1] above, wherein the Nb content is 0.1 or less in atomic ratio of Nb / (Nb + Sn). [5] The oxide sputtering target according to [1] above, wherein the Nb content is 0.02 or more in atomic ratio of Nb / (Nb + Sn). [6] The oxide sputtering target according to the above item [1], which has a volume resistivity of 50 Ω cm or less. [7] A method for producing the oxide sputtering target according to any one of the above items [1] to [6], comprising: ２ Powder and Nb ２ O ５ The powders are mixed and pulverized to obtain a median diameter D ５０ and sintering the obtained mixed powder in air or in an oxygen atmosphere at a sintering holding temperature of 1400°C or more and less than 1550°C. [8] A method for producing an oxide sputtering target according to the above item [7], wherein an oxygen atmosphere is used during cooling after sintering. [9] A method for producing an oxide sputtering target according to the above item [7], wherein a cooling rate is 1°C / min or more and 10°C / min or less in the temperature range from the holding temperature to 900°C.

[0012] According to the present disclosure, it is possible to provide an oxide sputtering target containing niobium, tin, and oxygen, and having a low volume resistivity and a high relative density, and a method for producing the same.

[0013] Below, the present disclosure will be described with reference to specific embodiments, but each configuration and combination thereof in each embodiment is merely an example, and addition, omission, substitution, and other modifications of configurations are possible as appropriate within the scope that does not deviate from the gist of the present disclosure.

[0014] The oxide sputtering target according to an embodiment of the present disclosure contains niobium (Nb), tin (Sn), and oxygen (O), and contains Nb in an atomic ratio of Nb / (Nb+Sn) of 0.01 or more and 0.2 or less, has a relative density of 99.5% or more, and a volume resistivity of 100 Ω cm or less. The oxide sputtering target according to this embodiment has a high relative density, which is expected to reduce particles during sputtering, and a low volume resistivity, which is expected to enable stable DC sputtering, which enables high-speed film formation.

[0015] The oxide sputtering target according to this embodiment contains niobium (Nb), tin (Sb), and oxygen (O). Impurities may be mixed in during the process of producing the sputtering target (raw materials, mixing, sintering, etc.), but the impurities may be contained within a range that does not significantly affect the properties of the sputtering target, and preferably the total impurity content is 0.1 mass% or less.

[0016] The oxide sputtering target according to this embodiment contains niobium (Nb) in an atomic ratio of Nb / (Nb + Sn) of 0.01 or more and 0.2 or less. By setting the atomic ratio of Nb / (Nb + Sn) to 0.01 or more and 0.2 or less, a thin film formed therefrom can be realized with high electrical conductivity and high transmittance in the visible light region. Preferably, the atomic ratio of Nb / (Nb + Sn) is 0.02 or more, and preferably the atomic ratio of Nb / (Nb + Sn) is 0.1 or less.

[0017] The oxide sputtering target according to this embodiment has a relative density of 99.5% or more. The higher the relative density, the more likely it is that particles will be reduced during sputtering. The relative density is preferably 99.6% or more, more preferably 99.7% or more, and particularly preferably 99.8% or more. As described above, when sintering is performed by hot pressing, the volume resistivity can be reduced, but it can be difficult to obtain a high-density sintered body. However, according to the present disclosure, by appropriately controlling the sintering conditions, an oxide sputtering target having a low volume resistivity and a high relative density can be obtained.

[0018] The oxide sputtering target according to this embodiment has a volume resistivity of 100 Ω cm or less. A lower volume resistivity has the advantage that DC sputtering, which allows high-speed film formation, can be stably performed. Preferably, the volume resistivity is 75 Ω cm or less, more preferably 50 Ω cm or less, and particularly preferably 40 Ω cm or less.

[0019] The oxide sputtering target according to this embodiment preferably has a coefficient of variation of the volume resistivity on the sputtering surface of 0.25 or less. More preferably, it is 0.20 or less. The sputtering surface is the surface that faces the substrate for film formation, and the smaller the coefficient of variation of the volume resistivity on the sputtering surface, the more stable the DC sputtering becomes. The coefficient of variation is calculated from the following formula: Coefficient of variation (CV) = (standard deviation) / (arithmetic mean value) When the area of ​​the sputtering surface of the sputtering target is expressed as S cm ２ When the length of the periphery is L cm, the distance between the measurement points on the sputtering surface is (L １／２ ) / 1.5 (cm) or more, the number of measurement points is set to the smallest (positive number) equal to or greater than the number expressed by 3 × S / L, the volume resistivity is measured at each measurement point, and the arithmetic mean value and standard deviation are calculated. For example, in the case of a circular sputtering target with a diameter of 10 cm, the calculation results are that the distance between measurement points is 3.74 cm and the number of measurement points is 7.50, so the volume resistivity is measured at any eight points spaced 3.74 cm or more apart, and the arithmetic mean value and standard deviation of the eight points are calculated.

[0020] A method for manufacturing an oxide sputtering target according to an embodiment of the present disclosure will be described. However, the manufacturing conditions and the like below are not limited to the disclosed range, and it is clear that some omissions and modifications may be made. Note that detailed descriptions of well-known manufacturing steps and processing operations will be omitted to avoid unnecessarily obscuring the disclosed manufacturing method.

[0021] (Raw material powder) As the raw material powder, tin oxide (SnO ２ ) powder, niobium oxide (Nb ２ O ５ ) powder. ２ The powder has a median diameter (D ５０ ): 0.1 to 10 μm is preferably used. ２ O ５ The powder has a median diameter (D ５０ It is preferable to use raw material powder with a purity of 99.9% by mass or more. The raw material powder may be calcined.

[0022] (Mixing and grinding process) The raw material powders are weighed to have the desired composition ratio (content ratio of the sintered body), and mixed and ground. There are various grinding methods depending on the desired particle size and the material to be ground, and wet or dry ball mills, vibration mills, bead mills, etc. can be used. To obtain uniform and fine crystal particles, a bead mill mixing method is preferred, which has high efficiency in breaking down agglomerates in a short time and also provides a good dispersion state of additives. Zirconia grinding balls are preferably used as the grinding media. The median diameter (D ５０ ): It is preferable that the thickness is 0.1 μm or more and 0.6 μm or less.

[0023] (Sintering process) If sintering is performed in a vacuum atmosphere or an inert atmosphere, tin oxide is reduced, resulting in a decrease in the relative density of the sintered body. Therefore, the sintering process is preferably performed in air or an oxygen atmosphere. The sintering holding temperature is preferably 1400°C or higher and lower than 1550°C, and the holding time is preferably 1 hour to 20 hours. If the holding temperature is too low, the relative density of the sintered body will not increase sufficiently, while if the holding temperature is too high, the relative density will decrease due to the evaporation of tin oxide and niobium oxide. However, the sintering holding temperature depends on the composition and the median diameter D of the powder. ５０ For example, Nb, which has a low melting point, is preferably used. ２ O ５ The amount is large, and the median diameter D ５０ The smaller the condition, the higher the density of the sintered body can be obtained even at low sintering temperature. ２ O ５ In the composition with a large amount, the median diameter D ５０ When the sintering temperature is about 1400°C, a high density sintered body can be obtained. ２ O ５ In the composition with a small amount, the median diameter D ５０ When the particle size is about 0.3 μm, a high density sintered body can be obtained by setting the sintering temperature at about 1550° C. The atmosphere during sintering is preferably an oxygen atmosphere (85 to 100 vol %).

[0024] (Temperature-reducing conditions) The sintering temperature is maintained for a certain period of time, and then the temperature is reduced. During the temperature reduction, it is preferable to switch the atmosphere in the sintering furnace from an oxygen atmosphere to an air atmosphere, a nitrogen atmosphere, or another atmosphere with an oxygen content of 25 vol% or less. If the temperature is reduced in an oxygen atmosphere, a large amount of oxygen is incorporated into the sintered body, reducing the number of oxygen vacancies that serve as carrier sources, thereby increasing the volume resistivity of the sintered body. Furthermore, in the temperature range from the holding temperature to 900°C, the temperature reduction rate is preferably 10°C / min or less and 1°C / min or more. By setting the temperature reduction rate to 10°C / min or less, the variation in volume resistivity can be suppressed. Furthermore, if the temperature reduction rate is less than 1°C / min, the temperature reduction time becomes longer, which makes it easier for more oxygen to be incorporated into the sintered body, thereby increasing the volume resistivity of the sintered body. However, the temperature reduction rate outside the above-mentioned specified temperature range is not particularly limited, and any temperature reduction rate can be adopted.

[0025] (Regarding Finishing) The sintered body obtained through the above-mentioned sintering process can be processed into a desired shape using a processing machine such as a surface grinder, a cylindrical grinder, or a machining device, as necessary. There are no particular restrictions on the shape of the sputtering target, and it can be a flat disk, a rectangle, a cylinder, or the like. Furthermore, if necessary, the sputtering target can be bonded to a backing plate for use.

[0026] The following description will be given based on examples and comparative examples. Note that these examples are merely examples and are not intended to limit the scope of the present invention. That is, the present invention is limited only by the scope of the claims and includes various modifications other than the examples included in this disclosure. Note that, since sputtering targets are produced by machining a sintered body, the physical properties of the sputtering target are, in principle, equivalent to those of the sintered body.

[0027] The evaluation methods used in the examples and comparative examples are as follows. (Composition analysis of sintered body) The composition of the sintered body was analyzed using the following apparatus. Apparatus: SPS3500DD manufactured by SII Corporation Method: ICP-OES (inductively coupled plasma optical emission spectroscopy)

[0028] (Volume Resistivity of Sintered Body) The volume resistivity of the sintered body was measured using the following device. Device: Resistivity Measuring Device Σ-5+ manufactured by NPS System: Constant Current Application Method: DC 4-Probe Method Measurement Temperature: Room temperature (20 to 25°C)

[0029] (Relative Density of Sintered Body) The relative density was calculated using the following formula: Relative density (%) = Archimedes density / true density × 100 Archimedes density: A measurement sample was prepared by grinding the top and bottom surfaces of the sintered body to a thickness of 1 mm, and grinding the outer peripheral surface to a thickness of 5 mm, and the Archimedes density was calculated using the Archimedes method. True density: The sintered body was subjected to a component analysis, and the oxide mass ratio (mass%) was calculated by converting the atomic ratio (at%) of each of Sn and Nb to the total of 100 at% of the constituent elements Sn and Nb obtained by the analysis, and the SnO ２ , Nb ２ O ５ The true density was calculated using the theoretical density of ３ )=(W1+W2) / (W1 / (6.95)+W2 / (4.47))×100 W1:SnO ２ Mass ratio (mass%) W2: Nb ２ O ５ Mass ratio (mass%) of the theoretical density: SnO ２ : 6.95 g / cm ３ Nb ２ O ５ : 4.47 g / cm ３

[0030] Example 1 SnO ２ powder, Nb ２ O ５ Powders are prepared, weighed and mixed to obtain the desired ratio, and then the median diameter D ５０ The mixed powder was then filled into a die and crushed under a pressure of 500 kgf / cm. ２ After press molding under the conditions of 1 minute holding time, the surface pressure was 1760 kgf / cm ２The compact was subjected to cold isostatic pressing (CIP) under conditions of 1 minute and 1500°C holding time to obtain a compact. The obtained compact was subjected to atmospheric sintering by holding at 1500°C in an oxygen atmosphere, and then cooled at 10°C / min in air to produce a sintered body. The relative density, volume resistivity, and coefficient of variation of volume resistivity of the obtained sintered body were determined. The results are shown in Table 1. As shown in Table 1, a sintered body with good properties was obtained in Example 1.

[0031]

[0032] Example 2: SnO ２ powder, Nb ２ O ５ Powders are prepared, weighed and mixed to obtain the desired ratio, and then the median diameter D ５０ The mixed powder was then filled into a die and crushed under a pressure of 500 kgf / cm. ２ After press molding under the conditions of 1 minute holding time, the surface pressure was 1760 kgf / cm ２ The compact was subjected to cold isostatic pressing (CIP) under conditions of 1 minute, 1500°C, and 1 minute of holding time to obtain a compact. The obtained compact was subjected to atmospheric sintering by being held at 1500°C in an oxygen atmosphere, and then cooled at 1°C / min in air to produce a sintered body. The relative density and volume resistivity of the obtained sintered body were determined. The results are shown in Table 1. As shown in Table 1, in Example 2, a sintered body with good properties was obtained.

[0033] Example 3: SnO ２ powder, Nb ２ O ５ Powders are prepared, weighed and mixed to obtain the desired ratio, and then the median diameter D ５０ The mixed powder was then filled into a die and crushed under a pressure of 500 kgf / cm. ２ After press molding under the conditions of 1 minute holding time, the surface pressure was 1760 kgf / cm ２The compact was subjected to cold isostatic pressing (CIP) under conditions of 1 minute, 1500°C, and 1 minute of holding time to obtain a compact. The obtained compact was subjected to atmospheric sintering by holding at 1500°C in an oxygen atmosphere, and then cooled at 10°C / min in air to produce a sintered body. The relative density, volume resistivity, and coefficient of variation of volume resistivity of the obtained sintered body were determined. The results are shown in Table 1. As shown in Table 1, a sintered body with good properties was obtained in Example 3.

[0034] Example 4: SnO ２ powder, Nb ２ O ５ Powders are prepared, weighed and mixed to obtain the desired ratio, and then the median diameter D ５０ The mixed powder was then filled into a die and crushed under a pressure of 500 kgf / cm. ２ After press molding under the conditions of 1 minute holding time, the surface pressure was 1760 kgf / cm ２ The compact was subjected to cold isostatic pressing (CIP) under conditions of 1 minute and 1450°C holding time to obtain a compact. The obtained compact was subjected to atmospheric sintering by holding at 1450°C in an oxygen atmosphere, and then cooled at 10°C / min in air to produce a sintered body. The relative density and volume resistivity of the obtained sintered body were determined. The results are shown in Table 1. As shown in Table 1, a sintered body with good properties was obtained in Example 4.

[0035] (Comparative example 1) SnO ２ powder, Nb ２ O ５ Powders are prepared, weighed and mixed to obtain the desired ratio, and then the median diameter D ５０ The mixed powder was then filled into a die and crushed under a pressure of 500 kgf / cm. ２ After press molding under the conditions of 1 minute holding time, the surface pressure was 1760 kgf / cm ２ The compact was subjected to cold isostatic pressing (CIP) under conditions of 1 minute and 1450°C holding time to obtain a compact. The obtained compact was subjected to atmospheric sintering by holding at 1450°C in an oxygen atmosphere, and then cooled at 10°C / min in air to produce a sintered body. The relative density and volume resistivity of the obtained sintered body were determined. The results are shown in Table 1. As shown in Table 1, the sintered body of Comparative Example 1 had a low relative density.

[0036] (Comparative example 2) SnO ２ powder, Nb ２ O ５ Powders are prepared, weighed and mixed to obtain the desired ratio, and then the median diameter D ５０ The mixed powder was then filled into a die and crushed under a pressure of 500 kgf / cm. ２ After press molding under the conditions of 1 minute holding time, the surface pressure was 1760 kgf / cm ２ The compact was subjected to cold isostatic pressing (CIP) under conditions of 1 minute, 1500°C, and 1 minute of holding time to obtain a compact. The obtained compact was subjected to atmospheric sintering by being held at 1500°C in an oxygen atmosphere, and then the temperature was lowered at 5°C / min while still in the oxygen atmosphere to produce a sintered body. The relative density and volume resistivity of the obtained sintered body were determined. The results are shown in Table 1. As shown in Table 1, the sintered body of Comparative Example 2 had a low relative density and high resistance.

[0037] (Comparative Example 3) SnO ２ powder, Nb ２ O ５ Powders are prepared, weighed and mixed to obtain the desired ratio, and then the median diameter D ５０ The mixed powder was then filled into a die and crushed under a pressure of 500 kgf / cm. ２ After press molding under the conditions of 1 minute holding time, the surface pressure was 1760 kgf / cm ２ The compact was subjected to cold isostatic pressing (CIP) under conditions of 1 minute, 1550°C, and 1 minute of holding time to obtain a compact. The obtained compact was subjected to atmospheric sintering by being held at 1550°C in an oxygen atmosphere, and then the temperature was lowered at 3°C / min while still in the oxygen atmosphere to produce a sintered body. The relative density, volume resistivity, and coefficient of variation of volume resistivity of the obtained sintered body were determined. The results are shown in Table 1. As shown in Table 1, the sintered body of Comparative Example 3 had a low relative density and high resistance.

[0038] (Comparative Example 4) SnO ２ powder, Nb ２ O ５ Powders are prepared, weighed and mixed to obtain the desired ratio, and then the median diameter D ５０ The mixed powder was then filled into a die and crushed under a pressure of 500 kgf / cm. ２After press molding under the conditions of 1 minute holding time, the surface pressure was 1760 kgf / cm ２ The compact was subjected to cold isostatic pressing (CIP) under conditions of 1 minute, 1500°C, and 1 minute of holding time to obtain a compact. The obtained compact was subjected to atmospheric sintering by holding at 1500°C in an oxygen atmosphere, and then cooled at 1°C / min in air to produce a sintered body. The relative density and volume resistivity of the obtained sintered body were determined. The results are shown in Table 1. As shown in Table 1, the relative density of the sintered body in Comparative Example 4 was significantly low.

[0039] According to the present disclosure, there is provided an oxide sputtering target containing niobium, tin, and oxygen, and having low volume resistivity and high relative density, and a method for producing the same, which is useful for forming transparent electrodes for plasma displays, liquid crystal displays, organic EL displays, touch panels, solar cells, and the like, or thin films for semiconductor devices.

Claims

1. An oxide sputtering target containing niobium (Nb), tin (Sn), and oxygen (O), in which the Nb content is 0.01 or more and 0.2 or less in terms of the atomic ratio of Nb / (Nb+Sn), has a relative density of 99.5% or more, and has a volume resistivity of 100 Ω-cm or less.

2. The oxide sputtering target according to claim 1, wherein the coefficient of variation of the volume resistivity on the sputtering surface of the sputtering target is 0.25 or less.

3. The oxide sputtering target according to claim 1, wherein the coefficient of variation of the volume resistivity on the sputtering surface of the sputtering target is 0.20 or less.

4. The oxide sputtering target according to claim 1, containing Nb in an atomic ratio of Nb / (Nb+Sn) of 0.1 or less.

5. The oxide sputtering target according to claim 1, containing Nb in an atomic ratio of Nb / (Nb+Sn) of 0.02 or more.

6. The oxide sputtering target according to claim 1, which has a volume resistivity of 50 Ω·cm or less.

7. A method for producing an oxide sputtering target according to any one of claims 1 to 6, comprising the steps of: ２ Powder and Nb ２ O ５ The powder is mixed and pulverized to obtain a median diameter D ５０ and sintering the resulting mixed powder in air or in an oxygen atmosphere at a sintering temperature of 1400° C. or higher and lower than 1550° C.

8. The method for producing an oxide sputtering target according to claim 7, wherein an oxygen atmosphere is used when lowering the temperature after sintering.

9. The method for producing an oxide sputtering target according to claim 7, wherein the temperature drop rate is 1° C. / min or more and 10° C. / min or less in the temperature range from the holding temperature to 900° C.

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