KR20220036347A - Cu―W-O SPUTTERING TARGET AND OXIDE THIN FILM - Google Patents

Abstract

A sputtering target containing tungsten (W), copper (Cu), oxygen (O) and inevitable impurities, and a Cu-WO sputtering target with a volume resistivity of 1.0×10 ³ Ω·cm or less. It is a thin film containing tungsten (W), copper (Cu), oxygen (O) and inevitable impurities, and is an oxide thin film in which the content ratio of W and Cu satisfies 0.5≤W/(Cu+W)<1 in atomic ratio. . The object of the present invention is to provide a sputtering target with a low volume resistivity that is capable of forming a film with a high work function.

Description

Cu-W-O sputtering target and oxide thin film {Cu―W-O SPUTTERING TARGET AND OXIDE THIN FILM}

The present invention relates to a Cu-W-O sputtering target suitable for forming an oxide thin film with a high work function.

ITO (indium tin oxide) is used as a transparent electrode (anode) in light-emitting devices such as organic electroluminescence (organic EL) devices. Holes injected by applying voltage to the anode combine with electrons in the light-emitting layer via the hole transport layer. In recent years, the use of oxides with a higher work function than ITO has been studied for the purpose of improving charge injection efficiency into the hole transport layer. For example, in Non-Patent Document 1, as an oxide thin film in an organic semiconductor device, TiO ₂ , MoO ₂ , CuO, NiO, WO ₃ , V ₂ O ₅ , CrO ₃ , Ta ₂ O ₅ , Co ₃ O ₄ High work functions such as those have been reported.

As shown in Non-Patent Document 1, WO ₃ has a relatively high work function. This WO ₃ film can be formed using a sputtering target made of a tungsten oxide sintered body (Patent Documents 1 and 2), but in the WO ₃ single phase, it is difficult to increase the density of the sintered body, and the volume resistivity is high, making DC sputtering difficult. . Therefore, Patent Document 2 discloses that adding WO ₂ to WO ₃ achieves higher density of the sintered body, increases conductivity, and makes DC sputtering possible. Additionally, Patent Document 1 discloses increasing the density of the sintered body by hot pressing WO ₃ powder in an oxygen supply atmosphere.

Japanese Patent Publication No. 3-150357 Japanese Patent Publication No. 2013-76163

Mark T Greiner and Zheng-Hong Lu, "Thin-Film metal oxides in organic semiconductor devices: their electronic structures, work functions and interfaces", NPG Asia Materials (2013) 5, e55, 19 July 2013

As described above, as a film constituting an organic semiconductor device such as organic EL, an oxide film with a high work function is required. Materials that exhibit a high work function include WO ₃ and the like. However, when forming a film of WO ₃ or the like, there is a problem that DC sputtering capable of high-speed film formation cannot be performed because the volume resistivity of the sputtering target used for film formation is high. . In this regard, the present invention has been proposed to solve the above-mentioned problems, and its object is to provide a sputtering target with a low volume resistivity that is capable of forming a film with a high work function.

The present invention has been proposed to solve the above problems, and an aspect of the present invention that can solve the problems is a sputtering target containing tungsten (W), copper (Cu), oxygen (O) and inevitable impurities. , a Cu-WO sputtering target with a volume resistivity of 1.0×10 ³ Ω·cm or less.

According to the present invention, it is a sputtering target capable of forming a film with a high work function, and since the volume resistivity is low, DC sputtering is possible, which has the excellent effect of enabling high-speed film formation.

As described above, WO ₃ has a high work function, but it was difficult to manufacture a sputtering target with a low volume resistivity capable of DC sputtering in a WO ₃ single phase. In addition, when other oxide materials with a high work function (for example, CuO single phase) were used, the volume resistivity was similarly high and DC sputtering was difficult. With regard to this problem, the present inventors have conducted extensive research, and have obtained the knowledge that by producing a mixed system of CuO and WO ₃ , a sputtering target with a low volume resistivity capable of DC sputtering can be obtained while maintaining a high work function. This has led to the present invention.

The sputtering target (referred to as Cu-WO sputtering target) according to the embodiment of the present invention contains tungsten (W), copper (Cu), oxygen (O) and inevitable impurities, and has a volume resistivity of 1.0 × 10 ³ It is less than Ω·cm. If the volume resistivity of the sputtering target is 1.0×10 ³ Ω·cm or less, DC sputtering becomes possible and high-speed film formation thereby becomes possible. Preferably, the volume resistivity is 1.0×10 ² Ωcm or less. As a result, high-speed film formation by more stable DC sputtering becomes possible.

The sputtering target according to the present embodiment contains W, Cu, O, and inevitable impurities, and the content ratio of W and Cu is preferably W/(Cu+W)≥0.5 in atomic ratio. In the case of W/(Cu+W)<0.5, there are cases where the volume resistivity becomes high and the desired high work function cannot be obtained. Preferably, W/(Cu+W)≥0.7, more preferably, W/(Cu+W)≥0.8, and even more preferably W/(Cu+W)≥0.9. In addition, in the case of WO ₃ single phase, as described above, the volume resistivity of the sputtering target is high, so W/(Cu+W)<1. In addition, the above-mentioned unavoidable impurities are impurities mixed in raw materials, manufacturing processes, etc., and may contain an amount that does not particularly affect characteristics such as work function, and as long as it is 0.1 wt% or less, there is no particular problem.

The sputtering target according to this embodiment preferably has a relative density of 95% or more. Preferably, the relative density is 98% or more. Such a high-density sputtering target can prevent cracks or fissures during sputtering and reduce particles during film formation. Additionally, the relative density of the sputtering target is also related to the volume resistivity, and as the value of the relative density decreases, the volume resistivity tends to increase. Therefore, in order to lower the volume resistivity, it is necessary to strictly adjust the manufacturing method and manufacturing conditions of the sputtering target in addition to the W and Cu content ratio of the sputtering target to increase the relative density.

The sputtering target according to one embodiment of the present invention has a work function of 4.5 eV or more. By using a sputtering target with such a high work function, a film with a high work function can be produced. And, such a high work function film can improve the charge injection efficiency into the hole transport layer in organic semiconductor devices such as organic EL and organic solar cells, and can be expected to improve luminous efficiency or conversion efficiency. .

Below, the manufacturing method of the sputtering target according to this embodiment is shown. However, it is clear that the following manufacturing conditions, etc. are not limited to the disclosed range, and that some omissions or changes may be made.

As raw material powder, tungsten oxide (WO ₃ ) powder and copper oxide (CuO) powder are prepared, and these raw material powders are weighed so that the desired composition ratio is obtained. As copper oxide, in addition to CuO, Cu ₂ O and the like can also be used. Next, wet grinding is performed using zirconia beads with a ball diameter of 0.5 to 3.0 mm. Then, pulverization is performed until the median particle size becomes 0.1 to 5.0 μm, and then granulation is performed. Next, the obtained granulated powder is press molded. The press pressure is preferably 300 to 400 kgf/cm2. Afterwards, cold isostatic pressing (CIP) is performed. The CIP pressure is preferably 1000 to 2000 kgf/cm2. Next, the obtained molded body is sintered at normal pressure in an oxygen flow for 10 to 20 hours. At this time, the sintering temperature is preferably 900°C or more and less than 950°C. If it is below 900°C, a high-density sintered body cannot be obtained. On the other hand, if it is above 950°C, it is not preferable because CuWO ₄ , which is a complex oxide of WO ₃ and CuO, reacts with the alumina sintered member and further dissolves. After that, the obtained sintered body can be cut or polished into the target shape to produce a sputtering target. Additionally, when hot press sintering is used, there are cases where CuO is reduced to Cu by the carbon sintered member, resulting in severe consumption of the member.

In the present specification, various physical properties of sputtering targets and the like were analyzed using the following measurement methods.

(Composition of sputtering target and film)

Device: SPS3500DD manufactured by SII

Method: ICP-OES (Inductively Coupled Plasma Luminescence Spectrometry)

(Component composition of the membrane)

Device: JXA-8500F made by JEOL

Method: Electron Beam Microanalyzer (EPMA)

Acceleration voltage: 5 to 10 keV

Irradiation current: 2.0×10 ^-7 to 2.0 to 10 ^-8 A

Probe diameter: 10㎛

Five smooth film-forming areas without adhesion of dust or the like and where the substrate surface was not visible were selected, point analysis was performed, and their average composition was calculated.

(Volume resistivity of sputtering target)

The volume resistivity of the sputtering target was measured at 5 points on the surface of the sputtering target (1 point at the center and 4 points near the outer periphery), and was taken as the average value. For the measurement, the following device was used.

Device: Resistivity meter Σ-5+ manufactured by NPS

Method: Constant current application method

Method: Direct current four probe method

(About the relative density of the sputtering target)

Relative density (%) = Archimedes density / true density × 100

Archimedes density: A small piece is cut from the sputtering target, and the density is calculated from the small piece using the Archimedes method.

True density: Calculate the atomic ratio of Cu and W from elemental analysis. From the atomic ratio, the weight of Cu in terms of CuO is set to a (wt%), and the weight of W in terms of WO ₃ is set to b (wt%), and the weight of Cu in terms of WO ₃ is set to b (wt %). Calculate the true density (g/cm3)=100/(a/d _CuO +b/d _WO3 ) by setting the theoretical densities as d _CuO and d _WO3 , respectively. Additionally, the theoretical density of CuO is set to _dCuO = 6.31g/cm3, and the theoretical density of _WO3 is set to _dWO3 = 7.16g/cm3.

(about work function)

For the bulk body (sputtering target), samples with a length of 20 mm, a width of 10 mm, and a thickness of 5 to 10 mm were produced. The measurement surface was polished using No. 2000 polishing paper. Additionally, regarding the sputtered film, a sample of 20 x 20 mm formed on a Si substrate was produced and measured under the following conditions. Additionally, the work function measurement result does not depend on the sample size. Additionally, if the measurement surface is not polished or is polished with low-count abrasive paper and the polishing of the surface is insufficient, the work function cannot be measured accurately, and the value may be measured to be high.

Method: Atmospheric photoelectron spectroscopy

Device: Ricken Geikise AC-5 device

Conditions: Range of measurable work function: 3.4eV to 6.2eV

Light source power: 2000W

[Example]

Hereinafter, description will be made based on examples and comparative examples. In addition, this embodiment is only an example and is not limited by this example at all. In other words, the present invention is limited only by the scope of the patent claims, and includes various modifications other than the embodiments included in the present invention.

(Example 1)

CuO powder and WO ₃ powder were prepared, and their powders were weighed as CuO:WO ₃ =50:50 (mol%). Next, wet ball mill mixing and grinding was performed for 24 hours using 3.0 mm zirconia beads, and mixed powder with a median diameter of 0.8 μm or less was obtained. Next, this mixed powder was pressed under the conditions of a surface pressure of 400 kgf/cm 2 and then CIP was performed under the conditions of a pressure of 1800 kgf/cm 2 to produce a molded body.

Next, a sintered body was produced by sintering at normal pressure in an oxygen flow at a sintering temperature of 940°C for 10 hours. Afterwards, this sintered body was machined and finished into a sputtering target shape.

As a result of evaluating the sputtering target obtained in Example 1, the relative density was 103.3% and the volume resistivity was 1.0×10 ³ Ω·cm. Additionally, as a result of measuring the work function of the sputtering target, a work function of 4.5 eV and a high work function was obtained. The above results are shown in Table 1. In addition, as a result of analyzing the composition of the sputtering target, it was confirmed that there was almost no change from the ratio when the raw materials were added.

(Examples 2 to 5)

CuO powder and ₃ WO powder were prepared, and their powders were weighed so that the molar ratio shown in Table 1 was obtained. Next, wet ball mill mixing and grinding was performed for 24 hours using 3.0 mm zirconia beads, and mixed powder with a median diameter of 0.8 μm or less was obtained. Next, this mixed powder was pressed under the conditions of a surface pressure of 400 kgf/cm2, and then CIP was performed under the conditions of a pressure of 1800 kgf/cm2 to produce a molded body.

Next, a sintered body was produced by sintering at normal pressure in an oxygen flow at a sintering temperature of 940°C for 10 hours. Afterwards, each sintered body was machined and finished into a sputtering target shape.

The sputtering targets of Examples 2 to 5 all had a relative density of 99% or more and a volume resistivity of 1.0×10 ³ Ω·cm or less. In addition, as a result of measuring the work functions of the sputtering targets, all of them had a high work function of 4.5 eV. In addition, as a result of analyzing the composition of the sputtering target, it was confirmed that there was almost no change from the ratio when the raw materials were added.

(Comparative Example 1)

In Comparative Example 1, only CuO powder was used and WO ₃ powder was not used. The Cu powder was mixed and pulverized using a wet ball mill for 24 hours using 3.0 mm zirconia beads to obtain a mixed powder with a median diameter of 0.8 μm or less. Next, this mixed powder was pressed under the conditions of a surface pressure of 400 kgf/cm2, and then CIP was performed under the conditions of a pressure of 1800 kgf/cm2 to produce a molded body.

Next, a sintered body was produced by sintering at normal pressure in an oxygen flow at a sintering temperature of 950°C for 10 hours. Afterwards, this sintered body was machined and finished into a sputtering target shape.

As a result of evaluating the sputtering target obtained in Comparative Example 1, the relative density was 98.3% and the volume resistivity was 3.3×10 ⁵ Ω·cm. Additionally, the work function of the sputtering target was measured and found to be 4.2 eV. In addition, as a result of analyzing the composition of the sputtering target, it was confirmed that there was almost no change from the ratio when the raw materials were added.

(Comparative Examples 2, 3)

In Comparative Examples 2 and 3, only WO ₃ was used and CuO was not used. WO was subjected to wet ball mill mixing and grinding for 24 hours using 3.0 mm zirconia beads for ₃ minutes to obtain mixed powder with a median diameter of 0.8 μm or less. Next, this mixed powder was pressed under the conditions of a surface pressure of 400 kgf/cm2, and then CIP was performed under the conditions of a pressure of 1800 kgf/cm2 to produce a molded body.

Next, in an oxygen flow, the sintering temperature was set to 1100°C (Comparative Example 2) and 940°C (Comparative Example 3), and sintering was performed at normal pressure for 10 hours to produce a sintered body. Afterwards, this sintered body was machined and finished into a sputtering target shape.

As a result of evaluating the sputtering targets obtained in Comparative Examples 2 and 3, the relative density was less than 95% and the volume resistivity was 1.0 × 10 ³ Ω·cm sec. Additionally, the work function of the sputtering target was measured and found to be 4.4 eV. In addition, as a result of analyzing the composition of the sputtering target, it was confirmed that there was almost no change from the ratio when the raw materials were added.

(Comparative Example 4)

CuO powder and WO ₃ powder were prepared, and their powders were weighed as CuO:WO ₃ =30:70 (mol%). Next, wet ball mill mixing and grinding was performed for 24 hours using 3.0 mm zirconia beads, and mixed powder with a median diameter of 0.8 μm or less was obtained. After pressurizing this mixed powder under the conditions of a surface pressure of 400 kgf/cm2, CIP was performed under the conditions of a pressure of 1800 kgf/cm2 to produce a molded body.

Next, a sintered body was produced by sintering at normal pressure in an oxygen flow at a sintering temperature of 850°C for 10 hours. Afterwards, this sintered body was machined and finished into a sputtering target shape.

As a result of evaluating the sputtering target obtained in Comparative Example 4, the volume resistivity was 3.1×10 ⁴ Ω·cm.

Next, sputter film formation was performed using the sputtering target of Example 3. In addition, the film formation conditions were as follows. As a result of measuring the work function of the obtained sputter film, the desired high work function was obtained as 4.6 eV under Ar gas and 4.8 eV under Ar gas + 6% O ₂ . In addition, as a result of analyzing the components of the sputtered film, it was confirmed that there was almost no change from the ratio when the raw materials were added.

(Tabernacle conditions)

Device: Canon Anervaje SPL-500 sputter device

Substrate: Silicone substrate

Film formation power density: 1.0W/㎠

Tabernacle atmosphere: Ar or Ar+6% O ₂

Gas pressure: 0.5Pa

Film thickness: 50nm

The Cu-W-O sputtering target according to the embodiment of the present invention has a low volume resistivity, enables DC sputtering, has a high relative density, does not cause cracks or cracks in the target during film formation, and is at a practical and commercial level. It can be used in The present invention is particularly useful for forming transparent electrodes in light-emitting devices such as organic electroluminescence devices.

Claims (7)

A Cu-WO sputtering target that contains tungsten (W), copper (Cu), oxygen (O) and inevitable impurities, and has a volume resistivity of 1.0×10 ³ Ω·cm or less. The Cu-W-O sputtering target according to claim 1, wherein the relative density is 95% or more. The Cu-W-O sputtering target according to claim 1, wherein the content ratio of W and Cu satisfies 0.5≤W/(Cu+W)<1 in atomic ratio. The Cu-W-O sputtering target according to claim 2, wherein the content ratio of W and Cu satisfies 0.5≤W/(Cu+W)<1 in atomic ratio. The Cu-W-O sputtering target according to any one of claims 1 to 4, wherein the work function satisfies 4.3 eV or more. It is a thin film containing tungsten (W), copper (Cu), oxygen (O) and inevitable impurities, and the oxide content of W and Cu satisfies 0.5≤W/(Cu+W)<1 in atomic ratio. pellicle. The oxide thin film according to claim 6, wherein the work function satisfies 4.5 eV or more.