Sputtering target and method of manufacturing the same

Abstract

The present invention addresses the problem of providing a sputtering target suitable for the formation of a semiconductor film having a low carrier concentration and a high mobility. Provided is a sputtering target containing zinc (Zn), tin (Sn), gallium (Ga) and oxygen (O), in which Ga is contained in an amount of 0.15 to 0.50 inclusive in terms of a Ga / (Zn+Sn+Ga) atomic ratio, Sn is contained in an amount of 0.30 to 0.60 inclusive in terms of an Sn / (Zn+Sn) atomic ratio, and the volume resistivity of the sputtering target is 50 Ω·cm or less.

Description

[Technical Field]

[0001] The present invention relates to a sputtering target and a method for manufacturing the same. [Background technology]

[0002] Zn-Sn-O based (ZTO: Zinc-Tin-Oxide) materials are known as materials for transparent conductive films and semiconductor films. Transparent conductive films are used in, for example, solar cells, liquid crystal display devices, touch panels, etc. (Patent Document 1, etc.). Semiconductor films are used as semiconductor layers (channel layers) of thin film transistors (TFTs) (Patent Document 2, etc.). ZTO films are usually formed using a sputtering target made of a Zn-Sn-O based sintered body.

[0003] A Ga-Zn-Sn-O (GZTO) film is also known, in which the above-mentioned ZTO is doped with gallium (Ga). For example, Patent Documents 3 and 4 disclose the formation of a thin film using a sputtering target made from zinc oxide, gallium oxide, and tin oxide. Patent Document 3 aims to produce a high-density sputtering target with low bulk resistance and to provide a transparent, amorphous semiconductor film that can be selectively etched relative to a metal thin film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-36198 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-37161 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-18457 [Patent Document 4] Special Publication No. 2016-507004 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0005] When used as a semiconductor film, a ZTO film has a problem of high power consumption due to its high carrier concentration. Therefore, it is conceivable to adjust the film composition to lower the carrier concentration. However, as the carrier concentration decreases, the carrier mobility (also simply referred to as mobility) decreases accordingly, and the desired semiconductor characteristics cannot be obtained. In view of these circumstances, an object of the present invention is to provide a sputtering target suitable for forming a semiconductor film with a low carrier concentration and high mobility. [Means for solving the problem]

[0006] One embodiment of the present invention is a sputtering target containing zinc (Zn), tin (Sn), gallium (Ga), and oxygen (O), wherein the Ga content is such that the atomic ratio of Ga / (Zn+Sn+Ga) is 0.15 or more and 0.50 or less, and the Sn content is such that the atomic ratio of Sn / (Zn+Sn) is 0.30 or more and 0.60 or less, and the volume resistivity is 50 Ω cm or less. [Effects of the Invention]

[0007] The present invention has the excellent effect of providing a sputtering target suitable for forming a semiconductor film having a low carrier concentration and high mobility. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Semiconductor film] In semiconductor films, there is a positive correlation between carrier concentration and mobility; the higher the carrier concentration, the higher the mobility. Therefore, increasing the carrier concentration is considered to increase mobility, but this increases power consumption. In recent years, with the miniaturization of semiconductor devices, the problem of power consumption has become apparent, and there is a demand for reducing this. However, because there is a trade-off between mobility and power consumption, it is necessary to obtain a carrier concentration that satisfies both of these requirements.

[0009] The present inventors have conducted extensive research into the above-mentioned problem, and have found that a semiconductor film (sometimes simply referred to as a "film") containing zinc (Zn), tin (Sn), gallium (Ga), and oxygen (O) that satisfies formulas (1) and (2) can achieve a low carrier concentration and high mobility. (1)0.15≦Ga / (Zn+Sn+Ga)≦0.50 (2) 0.33≦Sn / (Zn+Sn)≦0.65 (In the formula, Ga, Zn, and Sn respectively represent the atomic ratio of each element in the film.)

[0010] If the Ga content in the film is less than 0.15 in terms of the atomic ratio of Ga / (Zn+Sn+Ga), the desired carrier concentration will be too high, resulting in an unexpected increase in power consumption. On the other hand, if the atomic ratio of Ga / (Zn+Sn+Ga) exceeds 0.50, the desired mobility will not be obtained. Preferably, the atomic ratio of Ga / (Zn+Sn+Ga) is 0.15 or more and 0.40 or less, and more preferably, the atomic ratio of Ga / (Zn+Sn+Ga) is 0.15 or more and 0.25 or less.

[0011] If the Sn content in the film is less than 0.33 in terms of the atomic ratio of Sn / (Sn+Zn), there is a problem that the rate of change in film properties (carrier concentration, mobility, volume resistivity) due to heat when the film is annealed increases. On the other hand, if the atomic ratio of Sn / (Sn+Zn) exceeds 0.65, the carrier concentration becomes too high, resulting in an unexpected increase in power consumption. Preferably, the atomic ratio of Sn / (Sn+Zn) is 0.33 or more and 0.60 or less, and more preferably, the atomic ratio of Sn / (Sn+Zn) is 0.33 or more and 0.50 or less.

[0012] The carrier concentration of the semiconductor film is 1.0 × 10 17 cm -3 It is preferably 1.0×10 or less. More preferably, it is 1.0×10 16 cm -3 or less, and more preferably 1.0 × 10 15 cm -3 If the carrier concentration is within the above range, power consumption can be reduced sufficiently.

[0013] The mobility of the semiconductor film is 5.0 cm 2 / V·s or more. More preferably, 10.0 cm 2 / V·s or more, and more preferably 12.0 cm 2 / V·s or more. If the mobility is within the above range, the desired semiconductor characteristics can be obtained.

[0014] Furthermore, the semiconductor film preferably has a refractive index of 2.15 or less for light with a wavelength of 405 nm. More preferably, the refractive index is 2.10 or less and 2.00 or more. By setting the refractive index within the above range, the effect of preventing scattering between media can be obtained.

[0015] Furthermore, the semiconductor film preferably has an extinction coefficient of 0.02 or less for light with a wavelength of 405 nm. More preferably, the extinction coefficient is 0.01 or less. By setting the extinction coefficient within the above range, the effect of high transmittance can be obtained.

[0016] [Sputtering target] Because sputtering deposition is performed in a vacuum, the metal components of the sputtering target are not lost or mixed with other metal components during the deposition process, and the composition of the sputtering target (atomic ratio of metal components) is usually reflected in the composition of the film. However, with GZTO sputtering targets, the sputtering rate varies depending on the metal components and crystalline phase, resulting in fluctuations in the film composition (hereinafter sometimes referred to as film composition fluctuations). In particular, the tin (Sn) ratio of the film becomes higher relative to the sputtering target.

[0017] As a result of extensive research into film composition variations, the present inventors have discovered that by adjusting the composition range of the sputtering target and devising a manufacturing method thereof, it is possible to form the desired semiconductor film described above by DC sputtering. In light of this discovery, the present embodiment provides a sputtering target that contains zinc (Zn), tin (Sn), gallium (Ga), and oxygen (O), satisfies formulas (3) and (4), and has a volume resistivity of 50 Ω cm or less. (3)0.15≦Ga / (Zn+Sn+Ga)≦0.50 (4) 0.30≦Sn / (Zn+Sn)≦0.60 (In the formula, Ga, Zn, and Sn each represent the atomic ratio of each element in the sputtering target.)

[0018] The Ga content in the sputtering target is 0.15 or more and 0.50 or less in atomic ratio of Ga / (Zn+Sn+Ga), preferably 0.15 or more and 0.40 or less in atomic ratio of Ga / (Zn+Sn+Ga), and more preferably 0.15 or more and 0.25 or less in atomic ratio of Ga / (Zn+Sn+Ga). The Sn content in the sputtering target is 0.30 or more and 0.60 or less in terms of the atomic ratio of Sn / (Zn+Sn), preferably 0.30 or more and 0.50 or less, more preferably 0.33 or more and 0.45 or less in terms of the atomic ratio of Sn / (Sn+Zn). If the composition of the sputtering target is within the above range, a semiconductor film having a desired composition can be formed.

[0019] The sputtering target according to this embodiment has a volume resistivity of 50 Ω·cm or less, preferably 30 Ω·cm or less, and more preferably 10 Ω·cm or less. When the volume resistivity of the sputtering target is low, stable film formation can be achieved during DC sputtering. In the present disclosure, the volume resistivity is measured as follows. Measuring device: Resistivity meter Σ-5+ Measurement method: constant current application method Measurement method: DC 4-probe method The volume resistivity of the surface of the sputtering target is measured at one location in the center and at four locations at 90-degree intervals around the periphery, and the average value is calculated.

[0020] The sputtering target according to this embodiment preferably has a relative density of 97% or more, more preferably 98% or more, and even more preferably 99% or more. A high-density sputtering target can reduce the amount of particles generated during film formation. The relative density is calculated from the following formula: Relative density (%) = (measured density) / (reference density) x 100 The reference density is a density value calculated from the theoretical density of the oxide of each constituent element of the sputtering target, excluding oxygen, and the mass ratio, and the theoretical density of each oxide is as follows: Theoretical density of Ga2O3: 5.95 g / cm 3 Theoretical density of SnO: 6.95 g / cm 3 Theoretical density of ZnO: 5.61 g / cm 3 The measured density is the weight of the sputtering target divided by the volume, and is calculated using Archimedes' method.

[0021] The sputtering target according to this embodiment preferably has an average crystal grain size of 10 μm or less. More preferably, the average crystal grain size is 5 μm or less. If the structure of the sputtering target is fine, the amount of particles generated during film formation can be reduced.

[0022] [Sputtering target manufacturing method] The sputtering target according to this embodiment can be manufactured, for example, as follows. However, it should be understood that the manufacturing method described below is merely exemplary and that the present embodiment is not limited to this manufacturing method. Furthermore, detailed descriptions of well-known processes will be omitted to avoid unnecessarily obscuring the manufacturing method.

[0023] (Mixing and grinding raw materials) As raw material powder, ZnO powder, SnO 2 pink These raw material powders are weighed and mixed to obtain a desired compounding ratio, and if necessary, are preferably pulverized to an average particle size (D50) of 1.5 μm or less.

[0024] (Pre-firing of mixed powder) The resulting mixed powder is calcined for 4 to 7 hours at 1000 to 1300° C. By calcining, composite oxides (Zn2SnO4 phase, ZnGa2O4 phase) can be obtained.

[0025] (hot press sintering) The mixed powder or calcined powder is filled into a carbon mold and subjected to pressure sintering (hot pressing) under vacuum or inert gas atmosphere. The hot pressing conditions are a sintering temperature of 950°C to 1100°C and a pressing pressure of 200 to 300 kgf / cm. 2 The holding time is preferably 1 to 4 hours. If the sintering temperature is too low, a high-density sintered body cannot be obtained, while if the sintering temperature is too high, compositional deviation occurs due to evaporation of ZnO. Note that if sintering is performed in the air without pressure (atmospheric atmospheric sintering), the volume resistivity of the sintered body increases and the density decreases, so hot-press sintering is required to obtain the desired sputtering target.

[0026] (Surface treatment) A sintered body is produced by the above steps, and then mechanical processing such as cutting and polishing is performed to produce a sputtering target. [Example]

[0027] 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 various modifications other than the examples are included in the present invention.

[0028] The film formation conditions using the sputtering target were as follows: The sputtering target and the film were evaluated using the following methods. (Regarding film formation conditions) Film formation principle: DC sputtering Film deposition equipment: ANELVA SPL-500 Sputtering target size: 6 inch diameter, 5 mm thick Substrate: Glass Film thickness: 60 to 900 nm Power: 2.74~5.48W / cm 2 Atmosphere: Ar + 2% O2, 0.5 Pa, 28 to 50 sccm

[0029] (Composition of sputtering targets) Method: ICP-OES (inductively coupled plasma optical emission spectroscopy) Equipment: SII SPS3500DD

[0030] (Grain size of sputtering target) A surface parallel to the sputtering surface of the sputtering target is observed with a scanning electron microscope (SEM), and the crystal grain size is determined by the evaluation method using the intercept method of JIS G0551.

[0031] (About the film composition) Measurement principle: FE-EPMA quantitative analysis Measuring device: JEOL JXA-8500F Measurement conditions: accelerating voltage 15 kV Irradiation current 2×10 -7 A Beam diameter 100 μm

[0032] (Carrier concentration of the film) Measurement principle: Hall measurement Measuring device: Lake Shore 8400 Measurement conditions: Measured on sample after annealing at 200°C

[0033] (Membrane mobility) Measurement principle: Hall measurement Measuring device: Lake Shore 8400 Measurement conditions: Measured on sample after annealing at 200°C

[0034] Example 1 ZnO powder, SnO 2 pink , Ga2O3 powder, and Ga2O3 powder were prepared, and these raw material powders were mixed together to obtain the composition ratio of the sputtering target shown in Table 1. Next, this mixed powder was pulverized by wet milling (using ZrO2 beads) to an average particle size of 1.5 μm or less, and then dried. The crushed powder was then filled into a carbon mold and sintered in an argon atmosphere at a temperature of 950°C and a pressure of 250 kgf / cm. 2 The hot pressing was carried out under the conditions of sintering time: 2 hours, and the obtained oxide sintered body was machined to have the shape of a sputtering target (diameter: 6 inches).

[0035] The relative density, average crystal grain size, and volume resistivity of the Zn-Sn-Ga-O sputtering target prepared above were measured. The results are shown in Table 1. When DC sputtering was performed using this sputtering target, no arcing occurred during sputtering, and stable sputtering was possible.

[0036] (Examples 2-8) As in Example 1, ZnO powder, SnO 2 pinkThese raw material powders were prepared to have the composition ratio of the sputtering target shown in Table 1, and then mixed. Next, this mixed powder was subjected to wet pulverization (using ZrO beads) to produce powder with an average particle size of 1.5 μm. The powder was crushed and dried, and then sieved through a 500 μm sieve. The crushed powder was then filled into a carbon mold and sintered under an argon atmosphere at temperatures of 950°C, 1020°C, and 1050°C with a pressure of 250 kgf / cm. 2 The resulting sintered body was machined to a shape of a sputtering target (diameter: 6 inches). The relative density, average crystal grain size, and volume resistivity of the resulting sputtering target were analyzed, and the results are shown in Table 1. Note that Examples 2-7 were produced to investigate the properties of the sputtering target, and no film was formed.

[0037] (Comparative Examples 1-6) As in Example 1, ZnO powder, SnO 2 pink , Ga2O3 powder were prepared, and these raw material powders were prepared and mixed so as to have the composition ratio of the sputtering target shown in Table 1. Note that in Comparative Examples 1-4, Ga2O3 powder was not mixed. Next, this mixed powder was wet milled (using ZrO2 beads) to an average particle size of 1.5 μm. The resulting material was crushed and dried, and then sieved through a 500 μm sieve. The crushed powder was then filled into a carbon mold and sintered under the conditions listed in Table 1. The resulting sintered body was then machined to form a sputtering target (6 inches in diameter). Comparative Examples 1-4 were subjected to hot press sintering, while Comparative Examples 5-6 were subjected to atmospheric sintering in the atmosphere at a sintering temperature of 1400°C for a sintering time of 2 hours. The relative density, average crystal grain size, and volume resistivity of the resulting sputtering targets were analyzed, and the results are shown in Table 1. Comparative Examples 5-6 had high volume resistivity, so it is assumed that DC sputtering is not possible.

[0038] [Table 1]

[0039] [Evaluation of semiconductor thin films] The sputtering targets prepared in Examples 1 and 8 were attached to a sputtering apparatus, and sputtering was carried out under the conditions described above to form films. The film compositions of Film Formation Examples 1 and 2 are shown in Table 2. For each film formation example, the carrier concentration, mobility, refractive index, and extinction coefficient were analyzed. As a result, the carrier concentration was 1.0 × 10 17 cm -3 The mobility below is 5.0 cm 2 The desired results were obtained, with a refractive index of 2.15 or less and an extinction coefficient of 0.02 or less. The results are shown in Table 2.

[0040] The sputtering targets prepared in Comparative Examples 1-4 were attached to a sputtering apparatus, and sputtering was carried out under the conditions described above to form films. The film compositions are shown in Table 2 as Film Formation Examples 12-15. Analysis of the carrier concentration, mobility, refractive index, and extinction coefficient was performed for each film formation example. As a result, the carrier concentration was 1.0×10 17 cm -3 Therefore, when used as such a semiconductor film, it is expected that power consumption will be high. Table 2 shows the analysis results for mobility, refractive index, and extinction coefficient.

[0041] To analyze the relationship between film composition and carrier concentration and mobility in detail, films with different compositions were deposited by simultaneous sputtering (co-sputtering) and the carrier concentration, mobility, etc. of each were measured. For co-sputtering, a ZnSnO sputtering target and a Ga2O3 sputtering target were used. The Ga concentration in the film was adjusted by changing the sputtering power, and the Zn and Sn concentrations in the film were adjusted using four types of ZnSnO sputtering rings with different compositions. The compositions of the four types of ZnSnO sputtering rings were Zn:Sn = 66.7 at%:33.3 at%, 60.0 at%:40.0 at%, 50.0 at%:50.0 at%, and 40 at%:60 at%.

[0042] The compositions of the films of Film Formation Examples 3-11 and 16-19 formed by the co-sputtering method are shown in Table 2. The carrier concentration, mobility, refractive index, and extinction coefficient of each of the obtained films were analyzed. Film Formation Example 3-11, which satisfied the following conditions: (1) 0.15≦Ga / (Zn+Sn+Ga)≦0.50, (2) 0.33≦Sn / (Zn+Sn)≦0.65, had a carrier concentration of 1.0×10 17 cm -3 Below, mobility is 5.0 cm 2 / V·s or more, the desired results were obtained. On the other hand, for Film Formation Example 16, which does not satisfy the above formula (1), the desired carrier concentration was not obtained, and for Film Formation Examples 17-19, which do not satisfy the above formula (2), the desired mobility was not obtained.

[0043] [Table 2] [Industrial Applicability]

[0044] The present invention has the excellent effect of providing a sputtering target suitable for forming a semiconductor film with a low carrier concentration and high mobility. The semiconductor film obtained by the present invention is useful as a semiconductor film for solar cells, liquid crystal display devices, transparent conductive films for touch panels, etc., and TFT channel layers, etc.

Claims

1. A sputtering target containing zinc (Zn), tin (Sn), gallium (Ga), and oxygen (O), wherein the Ga content is in an atomic ratio of Ga / (Zn+Sn+Ga) of 0.15 or more and 0.25 or less, and the Sn content is in an atomic ratio of Sn / (Zn+Sn) of 0.33 or more and 0.60 or less, and the sputtering target has a volume resistivity of 50 Ω cm or less.

2. 2. The sputtering target according to claim 1, having a relative density of 97% or more.

3. 3. The sputtering target according to claim 1, wherein the average crystal grain size is 10 μm or less.

4. A method for producing a sputtering target according to claim 1 or 2, comprising the steps of: ２ Powder, Ga ２ O ３ A method for manufacturing sputtering targets in which powders are weighed, mixed, and then hot-pressed for sintering.

5. The method for producing a sputtering target according to claim 4, wherein the mixed powder is calcined at 1000°C to 1300°C, and the calcined powder is hot-press sintered.

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