Oxide semiconductor thin film, thin film semiconductor device, method for manufacturing thin film semiconductor device, sputtering target, and method for manufacturing sputtering target

Abstract

[Problem] To provide an oxide semiconductor thin film capable of realizing a thin film transistor having a high-mobility active layer, a thin film semiconductor device using the oxide semiconductor thin film, and a method for manufacturing the thin film semiconductor device, and to provide a sputtering target that can be used to form the oxide semiconductor thin film, and a method for manufacturing the sputtering target. [Solution] The present invention provides an oxide semiconductor thin film comprising an amorphous oxide semiconductor mainly composed of an In-Ga-Ge-Zn-O oxide containing indium, gallium, germanium, and zinc, in which 70 < = In < = 90 at%, 0 < Ga < = 10 at%, 0 < Ge < = 10 at%, and 5 < = Zn < = 30 at%.

Description

Technical Field

[0001] The present invention relates to an oxide semiconductor thin film, a thin film semiconductor device and a method for manufacturing the same, and a sputtering target and a method for manufacturing the same. Background Art

[0002] A thin film transistor (TFT: Thin-Film Transistor) using an In-Ga-Zn-O-based oxide semiconductor film (IGZO) for an active layer can achieve a high mobility as compared with a TFT using a conventional amorphous silicon film for the active layer, and thus has been widely used in various displays in recent years (for example, refer to Patent Documents 1 to 3).

[0003] For example, Patent Document 1 discloses an organic EL display device in which an active layer of a TFT for driving an organic EL element is made of IGZO. Patent Document 2 discloses a thin film transistor in which a channel layer (active layer) is made of a-IGZO and the mobility is 5 cm 2 / Vs or more. Patent Document 3 discloses a thin film transistor in which an active layer is made of IGZO and the on / off current ratio is 5 digits or more.

[0004] In recent years, due to the requirements for higher resolution, lower power consumption, and higher frame rate in various displays, the demand for an oxide semiconductor having a higher mobility has been increasing. However, in a thin film transistor using IGZO for the active layer, it is difficult for the mobility to exceed 10 cm 2 / Vs. In addition, with the popularization of current-driven devices, an oxide semiconductor having a high mobility is required. However, due to the increase in mobility, there are problems such as variations in characteristics and processability caused by crystallization of the film, and TFT malfunction caused by high mobility and high carrier density.

[0005] For example, in Patent Document 4, it was found that when an oxide having an electron carrier concentration of 10 18 / cm 3 or more is used for the channel layer of a TFT, the on / off current ratio cannot be sufficiently obtained and it is not suitable for an enhancement-mode TFT. Therefore, an amorphous oxide containing microcrystals and having an electron carrier concentration of less than 10 18 / cm 3 was proposed. Prior Art Documents

[0006] Patent Documents Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-31750 Patent Document 2: Japanese Unexamined Patent Application Publication No. 2011-216574 Patent Document 3: WO2010 / 092810 Patent Document 4: Japanese Patent No. 5138163 Gazette Summary of the Invention Problems to be Solved by the Invention

[0007] In view of the above circumstances, an object of the present invention is to provide an oxide semiconductor thin film for a thin film transistor capable of realizing a high-mobility active layer, a thin film semiconductor device using the oxide semiconductor thin film, and a manufacturing method thereof. Another object is to provide a sputtering target capable of forming the above oxide semiconductor thin film and a manufacturing method thereof. Means for Solving the Problems

[0008] To achieve the above object, various studies were repeatedly conducted, and as a result, it was found that an oxide semiconductor mainly composed of In-Ga-Ge-Zn-O containing indium, gallium, germanium, and zinc, and having an electron carrier density of 1×10 18 or more and less than 1×10 20 / cm 3 can obtain a high-mobility film with a Hall mobility of 25 cm 2 / V·s or more for a single film. By suppressing its crystallinity, it has excellent processability and can stably drive TFTs, thus completing the present invention. The present invention is as follows.

[0009] The first aspect of the present invention is an oxide semiconductor thin film composed of an amorphous oxide semiconductor mainly composed of In-Ga-Ge-Zn-O containing indium, gallium, germanium, and zinc, 70≤In≤90at%, 0<Ga≤10at%, 0<Ge≤10at%, 5≤Zn≤30at%. The second aspect of the present invention is the oxide semiconductor thin film of the first aspect, having a Hall mobility of 25 cm 2 / V·s or more. The third aspect of the present invention is the oxide semiconductor thin film of the first aspect, having a carrier density of 1.0×10 18 / cm 3 or more and less than 1.0×10 20 / cm 3 . The fourth aspect of the present invention is the oxide semiconductor thin film of the first aspect, having an etching rate of 1 nm / sec or more when etched with an oxalic acid-based etchant or a sulfuric acid / nitric acid-based etchant. The fifth aspect of the present invention is the oxide semiconductor thin film of the first aspect, wherein 3≤Ga+Ge≤9.5at%. A sixth aspect of the present invention is the oxide semiconductor film of the first aspect, which further contains at least one additive element selected from Si, Ti, Ni, Y, Ca, Al, Mg, Nb, Ta, Zr, Ba, Hf, W, and Mo, and the total content of Ga, Ge, and the additive element is 10 at% or less. A seventh aspect of the present invention is a thin-film semiconductor device, which includes: an active layer containing an amorphous oxide semiconductor film with high mobility, a gate electrode provided on at least one surface of the active layer via a gate insulating film, and a source electrode and a drain electrode connected to the active layer, wherein the active layer is a thin-film semiconductor device containing the oxide semiconductor film of any one of the first to sixth aspects. An eighth aspect of the present invention is the thin-film semiconductor device of the seventh aspect, wherein the gate insulating film and the gate electrode are provided on the upper surface of the active layer, the source electrode and the drain electrode are provided on the upper surface side (i.e., this side of the upper surface) of the active layer, and in at least one of the upper surface and the lower surface of the active layer, there is a case where there is a semiconductor film having a carrier density smaller than that of the active layer. A ninth aspect of the present invention is the thin-film semiconductor device of the seventh aspect, wherein the gate insulating film and the gate electrode are provided on the lower surface of the active layer, the source electrode and the drain electrode are provided on the upper surface side (i.e., this side of the upper surface) of the active layer, and in at least one of the upper surface and the lower surface of the active layer, there is a case where there is a semiconductor film having a carrier density smaller than that of the active layer. A tenth aspect of the present invention is the thin-film semiconductor device of the ninth aspect, wherein an etching stop layer is provided on the upper surface of the active layer, and the source electrode and the drain electrode are provided on the etching stop layer on the upper surface side of the active layer. An eleventh aspect of the present invention is the thin-film semiconductor device of the seventh aspect, wherein the gate insulating film and the gate electrode are provided on both the upper surface and the lower surface of the active layer, the source electrode and the drain electrode are provided on the upper surface side of the active layer, and in at least one of the upper surface and the lower surface of the active layer, there is a case where there is a semiconductor film having a carrier density smaller than that of the active layer. A twelfth aspect of the present invention is a method for manufacturing the thin-film semiconductor device of the seventh aspect, which includes: a step of forming the active layer by sputtering, a step of patterning the active layer by etching, and a step of annealing the active layer. A thirteenth aspect of the present invention is a method for manufacturing the thin-film semiconductor device of any one of the eighth to eleventh aspects, which includes: a step of forming the active layer by sputtering, a step of patterning the active layer by etching, and a step of annealing the active layer. The 14th aspect of the present invention is a sputtering target for forming an oxide semiconductor film in any one of the 1st to 6th aspects, which is composed of an oxide sintered body mainly composed of an oxide of In-Ga-Ge-Zn containing indium, gallium, germanium, and zinc. The 15th aspect of the present invention is the sputtering target of the 14th aspect, and its density is 98% or more. The 16th aspect of the present invention is the sputtering target of the 14th aspect, wherein 70 ≤ In ≤ 90 at%, 0 < Ga ≤ 10 at%, 0 < Ge ≤ 10 at%, 5 ≤ Zn ≤ 30 at%, and the distribution of the L* value of SCI represented by the L*a*b* color system is within ±3 in the thickness direction. Advantages of the Invention

[0010] By forming an oxide semiconductor containing indium, gallium, germanium, and zinc and mainly composed of an oxide of In-Ga-Ge-Zn with a specified composition, the present invention can achieve an electron carrier density of 1 × 10 18 / cm 3 or more and less than 1 × 10 20 / cm 3 , a high mobility of 25 cm 2 / V·s or more for a single film, suppressed crystallinity, excellent processability, and an oxide semiconductor film capable of stably driving a TFT. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view showing an example of the structure of the thin film semiconductor device of the present invention. Figure 2 is a cross-sectional view showing an example of the structure of the thin film semiconductor device of the present invention. Figure 3 is a cross-sectional view showing an example of the structure of the thin film semiconductor device of the present invention. Figure 4 is a cross-sectional view showing an example of the structure of the thin film semiconductor device of the present invention. Figure 5 is a cross-sectional view showing an example of the structure of the thin film semiconductor device of the present invention. Figure 6 Shows the measurement results of the crystallinity of Samples 1 to 4 in Table 1. Figure 7 Shows measurement examples of Samples 23 and 24 showing local crystallinity. Figure 8 In (a) of the thin film semiconductor device 1, mobility and Vth are shown, in (b) PBTS is shown, and in (c) NBTS is shown. Figure 9 In (a) of the thin film semiconductor device 2, mobility and Vth are shown, in (b) PBTS is shown, and in (c) NBTS is shown. Figure 10 In the case of the thin film semiconductor device 3, (a) represents the mobility and Vth, (b) represents PBTS, and (c) represents NBTS. Figure 11 In the case of the thin film semiconductor device 4, (a) represents the mobility and Vth, (b) represents PBTS, and (c) represents NBTS. Figure 12 Represents the mobility and Vth of the thin film semiconductor devices 5 and 6. Detailed implementation mode

[0012] Next, the implementation mode of the present invention will be described with reference to the drawings.

[0013] [Oxide semiconductor thin film] The oxide semiconductor thin film of the present invention is composed of an amorphous oxide semiconductor mainly composed of an oxide of In-Ga-Ge-Zn containing indium, gallium, germanium, and zinc, where 70 ≤ In ≤ 90 at%, 0 < Ga ≤ 10 at%, 0 < Ge ≤ 10 at%, and 5 ≤ Zn ≤ 30 at%. In is the main element that increases the mobility and is the element that increases the mobility of Zn. Ga and Ge are elements that reduce the mobility, but are less likely to reduce the mobility compared to other elements. That is, in the present invention, by adding Ge to the composition of the representative IGZO (In-Ga-Zn-O) system as a high-mobility oxide semiconductor material to form a specified composition, an electron carrier density of 1 × 10 18 / cm 3 or more and less than 1 × 10 20 / cm 3 can be achieved, and the Hall mobility of the single film is 25 cm 2 / V·s or more, a high-mobility amorphous film with suppressed crystallinity, excellent processability, and capable of stably driving TFTs.

[0014] As described above, the contents of Ga and Ge are 0 < Ga ≤ 10 at%, 0 < Ge ≤ 10 at%, preferably 3 ≤ Ga + Ge ≤ 9.5 at%, more preferably 3.5 ≤ Ga + Ge ≤ 7.0 at%, and further preferably 3.5 ≤ Ga + Ge ≤ 6.0 at%. As described above, by controlling the contents of Ga and Ge within the above range, a specified mobility and carrier density can be achieved. That is, within the range of 3 ≤ Ga + Ge ≤ 9.5 at%, the Hall mobility is 25 cm 2 / V·s or more, and the carrier density is 1 × 10 18 ~5 × 10 19 / cm 3 , and within the range of 3.5 ≤ Ga + Ge ≤ 7.0 at%, the Hall mobility is 30 cm2 Above / V·s, the carrier density is 5×10 18 ~5×10 19 / cm 3 , in the range of 3.5 ≤ Ga + Ge ≤ 6.0 at%, the Hall mobility is 33 cm 2 Above / V·s, the carrier density is 7×10 18 ~5×10 19 / cm 3 . It should be noted that if the contents of Ga and Ge are more, it will become a film with a small mobility. The Hall mobility of the oxide semiconductor film of the present invention after annealing in the atmosphere at about 300 °C is 25 cm 2 Above / V·s, preferably 30 cm 2 Above / V·s, particularly preferably 33 cm 2 Above / V·s.

[0015] In addition, the carrier density after annealing in the atmosphere is 1.0×10 18 / cm 3 Above and less than 1.0×10 20 / cm 3 , preferably 5.0×10 18 / cm 3 Above and less than 5.0×10 19 / cm 3 . The band gap Eg of the oxide semiconductor film of the present invention is 2.4 eV or more and 2.8 eV or less. The oxide semiconductor film of the present invention can be etched at an etching rate of 1 nm / sec or more using any one of, for example, an oxalic acid-based etchant such as ITO06N·07N (manufactured by Kanto Chemical Co., Inc.), a mixed acid-based etchant of sulfuric acid and nitric acid, or other etchants. The oxide semiconductor film of the present invention may also contain other elements as long as it does not hinder the characteristics of the oxide In-Ga-Ge-Zn-O described above. As such additive elements, at least one element selected from Si, Ti, Ni, Y, Ca, Al, Mg, Nb, Ta, Zr, Ba, Hf, W, and Mo can be cited, and these elements can be contained within a range that does not hinder the above characteristics. These additive elements have the characteristic of reducing the mobility to a greater extent compared to Ga and Ge but being less likely to reduce the mobility compared to other elements. That is, these additive elements have the characteristic that even if added at 10 at% or less, for example, the mobility will not be significantly reduced. Such additive elements can be contained in a total content of 10 at% or less, and preferably the total content of Ga, Ge, and the additive elements is 10 at% or less. It should be noted that Sb and Sn also have the property of not easily reducing the mobility, similar to Ga and Ge. However, since good properties for processability, crystallinity, and stability of TFT characteristics cannot be obtained, Sb and Sn are preferably not contained in the present invention.

[0016] The method for forming the oxide semiconductor thin film of the present invention is not particularly limited. For example, it can be formed by sputtering using a sputtering target having the same composition as the composition to be formed, or it can be formed by an atomic layer deposition (ALD) method, a vacuum evaporation method, etc. As long as an amorphous oxide semiconductor thin film can be formed, the film formation method is not particularly limited.

[0017] In addition, the oxide semiconductor thin film of the present invention can be used as an active layer of a thin film semiconductor transistor such as a TFT, i.e., a thin film semiconductor device (device). The thin film semiconductor device having the oxide semiconductor thin film of the present invention includes an active layer containing a high-mobility amorphous oxide semiconductor thin film, a gate electrode provided via a gate insulating film on at least one surface of the active layer, and a source electrode and a drain electrode connected to the active layer, wherein the active layer contains the oxide semiconductor thin film of the present invention. That is, the oxide semiconductor thin film can be used, for example, as a high-mobility active layer in a thin film transistor such as a so-called top-gate field effect transistor, and a semiconductor device of a type having a semiconductor thin film with a carrier density smaller than that of the active layer on at least one of the upper and lower sides of the active layer can be fabricated. In addition, it can also be applied to the active layer of a field effect transistor having an etch stop layer (ESL) structure, a back-channel etch (BCE) structure, or a dual-gate (Double Gate) structure.

[0018] As a specific thin film semiconductor device, a structure can be cited in which the above-mentioned gate insulating film and the above-mentioned gate electrode are provided on the upper surface of the above-mentioned active layer, and the above-mentioned source electrode and the above-mentioned drain electrode are provided on the upper surface side of the above-mentioned active layer. Figure 1 It shows a structure of an example of this thin film semiconductor device.

[0019] Figure 1 It shows a schematic structure of an example of the thin film transistor of the present invention. The thin film transistor 100 of the present embodiment includes an active layer 11, a gate insulating film 12, a gate electrode 13, and an interlayer insulating film 14 on a substrate 10, and has a source electrode 15S and a drain electrode 15D led out from the active layer 11 via the interlayer insulating film 14.

[0020] The substrate 10 is typically a transparent glass substrate or a transparent glass substrate formed with a buffer layer film. The gate electrode 13 is typically composed of a single-layer metal film or a multi-layer metal film such as molybdenum (Mo), titanium (Ti), aluminum (Al), copper (Cu), etc., and is formed by, for example, sputtering. In the present embodiment, the gate electrode 13 is composed of molybdenum. The thickness of the gate electrode 13 is not particularly limited, and is, for example, 100 nm to 500 nm. The gate electrode 13 is formed by, for example, sputtering, ALD method, vacuum evaporation method, etc.

[0021] The active layer 11 serves as the channel layer of the thin film transistor 100. The film thickness of the active layer 11 is, for example, 10 nm to 100 nm. The active layer 11 is composed of the oxide semiconductor thin film of the present invention described above. The active layer 11 is formed by, for example, sputtering, ALD method, vacuum evaporation method, etc.

[0022] The gate insulating film 12 is formed between the gate electrode 13 and the active layer 11. The gate insulating film 12 is composed of, for example, a silicon oxide film (SiOx), a silicon nitride film (SiNx), or a stacked film thereof. The film forming method is not particularly limited, and can be a CVD method, a sputtering method, an evaporation method, etc. The film thickness of the gate insulating film 12 is not particularly limited, and is, for example, 50 nm to 400 nm.

[0023] The interlayer insulating film 14 is formed so as to cover the gate insulating film 12 and the gate electrode 13. The interlayer insulating film 14 is composed of, for example, a silicon oxide film (SiOx), a silicon nitride film (SiNx), or a stacked film thereof. The film forming method is not particularly limited, and can be a CVD method, a sputtering method, an evaporation method, etc. The film thickness of the interlayer insulating film 14 is not particularly limited, and is, for example, 100 nm to 800 nm.

[0024] The source electrode 15S and the drain electrode 15D are formed separately from each other on the interlayer insulating film 14. The source electrode 15S and the drain electrode 15D can be composed of, for example, a single-layer metal film such as aluminum, molybdenum, copper, titanium, etc., or a multi-layer film of these metals. As described later, the source electrode 15S and the drain electrode 15D can be formed simultaneously by patterning the metal film. The thickness of the metal film is, for example, 100 nm to 1000 nm. The source electrode 15S and the drain electrode 15D are formed by, for example, sputtering, vacuum evaporation method, etc.

[0025] On at least one of the upper surface and the lower surface of the active layer 11 of the thin film transistor 100, a semiconductor thin film having a carrier density smaller than that of the active layer 11 can be provided. Figure 2 An example of such a thin film transistor is shown. Figure 2 The thin film transistor 100A of has semiconductor thin films 11A and 11B having a small carrier density on both the lower surface and the upper surface of the active layer 11. As the semiconductor thin films 11A and 11B, for example, materials of the In-Ga-Zn system with a carrier density of 1.0×10 15 / cm 3 ~1.0×10 18 / cm 3 can be cited, but it is not limited to the In-Ga-Zn system. In addition, like the active layer 11, the semiconductor thin films 11A and 11B are formed by, for example, sputtering, ALD, vacuum evaporation, etc.

[0026] The thin film transistor of the present invention is not limited to such a structure, and may also be a thin film transistor having the structure shown in Figures 3 - 5 . Figure 3 The thin film transistor 100B has a structure in which a gate electrode 13 is provided under the active layer 11, and has a structure in which the gate electrode 13, the gate insulating film 12, and the active layer 11 are stacked on the substrate 10, and the source electrode 15S and the drain electrode 15D are led out from the gate insulating film 12 and the active layer 11. Figure 4 The thin film transistor 100C has a structure in which an etch stop layer 16 is provided on the gate insulating film 12 and the active layer 11 of the thin film transistor 100B shown in Figure 3 . The etch stop layer 16 is formed of, for example, a silicon oxide film (SiOx), and there is no particular limitation on the film formation method, which may be a CVD method, a sputtering method, an evaporation method, etc. The film thickness of the etch stop layer 16 is not particularly limited, and is, for example, 50 nm to 300 nm.

[0027] Figure 5 The thin film transistor 100D is a double-gate TFT, and has a bottom gate electrode 13A on the lower surface side of the active layer 11 via a gate insulating layer 12A, and a top gate electrode 13B on the upper surface side via a gate insulating layer 12B, and the source electrode 15S and the drain electrode 15D are led out from the active layer 11.

[0028] In the structure of Figures 3 - 5 , a semiconductor thin film having a carrier density smaller than that of the active layer 11 may be provided on at least one of the upper surface and the lower surface of the active layer 11. It should be noted that the specific examples described above illustrate lateral transistors, but are not limited thereto, and of course, vertical transistors are also possible.

[0029] [Sputtering target] Next, the sputtering target of the present invention will be described.

[0030] The sputtering target can be a planar target or a cylindrical rotating target. The sputtering target is composed of a sintered body of an oxide containing In, Ga, Ge, and Zn, and the composition ratio is the same as that of the above-mentioned oxide semiconductor thin film, and the preferred composition ratio is also the same, so the repeated description is omitted.

[0031] The composition range of the oxide sintered body of the sputtering target of the present invention is composed of an oxide sintered body containing oxides of indium, gallium, germanium, and zinc, and the contents of In, Ga, Ge, and Zn are as described above.

[0032] The oxide sintered body constituting the sputtering target of the present invention may further contain at least one additive element selected from Si, Ti, Ni, Y, Ca, Al, Mg, Nb, Ta, Zr, Ba, Hf, W, and Mo.

[0033] In addition, the oxide sintered body of the present invention needs to be manufactured in a state where the distribution of the L* value of SCI represented by the L*a*b* color system is within ±3 in the thickness direction. This color distribution indicates whether sintering is carried out evenly. The oxides of the element composition of the present invention are prone to uneven sintering, and it is necessary to achieve the averaging of sintering according to the composition and flow rate of the atmosphere gas, etc. The uniformity of the color distribution is necessary both in the in-plane direction and the thickness direction. In particular, the distribution in the thickness direction is prone to unevenness, so the L* value of SCI in the thickness direction is specified, but the L* value of SCI in the in-plane direction also becomes a distribution within ±3. However, these values vary depending on the conditions of the sintering apparatus, so appropriate adjustment is required, but the key is to evaluate with the L* value of SCI finally represented by the L*a*b* color system.

[0034] The Hall mobility of the oxide semiconductor thin film sputtered from the oxide sintered body of the present invention is 25 cm 2 / V·s or more, preferably 30 cm 2 / V·s or more, particularly preferably 33 cm 2 / V·s or more. In addition, the carrier density is 1.0×10 18 / cm 3 or more and less than 1.0×10 20 / cm 3 , preferably 5.0×10 18 / cm 3 or more and less than 5.0×10 19 / cm 3 . In addition, the band gap Eg of the sputtered oxide semiconductor thin film is 2.4 eV or more and 2.8 eV or less.

[0035] In this way, the oxide semiconductor thin film formed using the sputtering target of the present invention can achieve 25 cm 2a high mobility of 1 / V·s or more, and a carrier density of 1.0×10 18 / cm 3 or more and less than 1.0×10 20 / cm 3 .

[0036] (Method for manufacturing a sputtering target) The method for manufacturing the sputtering target of the present invention is not particularly limited as long as it can produce an oxide sintered body having the above composition. For example, the following two manufacturing methods can be exemplified.

[0037] The first method is a method for manufacturing a sputtering target having an oxide sintered body by mixing indium oxide powder, zinc oxide powder, gallium oxide powder, and germanium oxide powder to form a molded body and firing the molded body at a temperature of 1100°C or higher and 1650°C or lower. The weight ratio of the raw material powders is determined to be the element ratio of the target oxide sintered body.

[0038] In addition, the second method is a method for manufacturing a sputtering target having an oxide sintered body by mixing indium, zinc, gallium, and germanium in the form of at least a part of oxides, hydroxides, or carbonates, molding the precursor powder obtained by pre-firing at 900°C to 1400°C into a molded body, and firing the molded body at a temperature of 1100°C or higher and 1650°C or lower. Here, the meaning of at least a part of indium, zinc, gallium, and germanium is that a part can be directly pre-fired in the form of an element, and the remaining elements can be combined as oxides or the like. It should be noted that the weight ratio of the raw material powders is determined to be the element ratio of the target oxide sintered body.

[0039] Hereinafter, the second method will be further exemplified and the manufacturing method will be described in detail. In the present embodiment, the raw material powders are granulated by a spray drying method capable of performing drying and granulation at one time. By adding a binder, a pulverization operation with poor pulverization properties is not required, and since spherical powders with good fluidity can be used, the composition distribution of the sputtering target is likely to become uniform.

[0040] The raw material powders contain at least oxides, hydroxides, or carbonates of indium, zinc, gallium, and germanium. In addition, powders of one or more selected from the oxides of the above-mentioned additive elements may be mixed. In addition, a dispersant or the like may be added to the mixing of the raw material powders.

[0041] As a method for pulverizing and mixing the raw material powders, a ball mill can be used. In addition to the ball mill, for example, other medium stirring mills such as a bead mill and a roll mill can also be used. A resin coating or the like can also be applied to the surface of the balls or beads as the stirring medium. Thereby, the mixing of impurities into the powder can be effectively suppressed.

[0042] The mixed particle powder is pre-fired at a temperature above 900 °C and below 1400 °C. When the firing temperature is lower than 900 °C, the composite oxide cannot be completely formed due to insufficient pre-firing. When the firing temperature exceeds 1400 °C, sintering is promoted by pre-firing, and the particle shape of the primary particles becomes larger. Therefore, the sintering density will not increase during the subsequent formal firing. The pre-fired powder is wet-crushed again with a ball mill or the like together with a dispersant, a binder, etc., and granulated by spray drying.

[0043] The average particle size of the granulated powder is 500 μm or less. When the average particle size of the granulated powder exceeds 500 μm, the generation of cracks or fissures in the green body becomes significant, and granular spots are generated on the surface of the fired body. If such a fired body is used as a sputtering target, it may cause abnormal discharge or particle generation.

[0044] The average particle size of the granulated powder is more preferably 20 μm or more and 100 μm or less. Thereby, the volume change (compression ratio) before and after CIP (Cold Isostatic Press) forming is small, the generation of cracks in the green body is suppressed, and a long-strip green body can be stably produced. It should be noted that when the average particle size is less than 20 μm, the powder is likely to fly, and the handling becomes difficult.

[0045] Here, the "average particle size" refers to the value at which the cumulative percentage of the particle size distribution measured by a sieve-type particle size distribution analyzer is 50%. In addition, as the value of the average particle size, the value measured by "Robot Sifter RPS-105M" manufactured by Seishin Enterprise Co., Ltd. is used.

[0046] The granulated powder is formed under a pressure of 100 MPa / cm 2 or more. Thereby, a sintered body with a relative density of 98% or more can be obtained. When the forming pressure is less than 100 MPa, the green body is easily damaged, the operation is difficult, and the relative density of the sintered body is reduced.

[0047] As the forming method, the CIP method is adopted. The CIP method can be a typical vertical load type longitudinal method, and a horizontal load type transverse method is preferred. This is because when a long-strip plate-shaped green body is produced by the longitudinal type CIP, the thickness deviation is caused by the powder displacement in the mold, or it breaks due to its own weight during the operation.

[0048] In addition, the green body is fired at 1100 °C to 1650 °C to become a sintered body. When the firing temperature is lower than 1100 °C, the conductivity and relative density are low, which is not suitable for the use of the target. On the other hand, when the firing temperature exceeds 1650 °C, a part of the components evaporate, the composition deviation of the fired body occurs, or the strength of the fired body is reduced due to the coarsening of the grains.

[0049] The formed body is fired in the atmosphere or an oxidizing atmosphere. Thereby, the target oxide sintered body is stably manufactured.

[0050] In the production of the granulated powder, powders having an average primary particle diameter of 0.3 μm or more and 1.5 μm or less are used. Thereby, the mixing and pulverization time can be shortened, and the dispersibility of the raw material powder in the granulated powder can be improved.

[0051] The angle of repose of the granulated powder is preferably 32° or less. Thereby, the fluidity of the granulated powder is improved, and the formability and sinterability are improved.

[0052] (Processing step) A sputtering target containing an In-Ga-Ge-Zn-O-based sintered body is produced by machining the fired body produced as described above into a plate shape having a desired shape, size, and thickness. The sputtering target is brazed to the backing plate.

[0053] According to the present embodiment, a long sputtering target having a length in the length direction exceeding 1000 mm can be produced. Thereby, a large sputtering target that is not a divided structure can be produced, so that deterioration of film characteristics that may be caused by sputtering of the bonding material (brazing filler metal) that invades the gap (seam) of the divided portion can be prevented, and stable film formation can be performed. In addition, particles caused by reattachment (redeposition) of sputtered particles accumulated in the above gap are hardly generated.

[0054] [Evaluation of sputtering target] (L* value of SCI represented by the L*a*b* color system) The L* value is measured by a spectrocolorimeter CM-700d manufactured by Konica Minolta Inc. with an SCI value (measurement method including regular reflection light). The measurement is performed at the center of the surface and cross section of the target. The L value is affected by the density and oxygen deficiency of the oxide. The higher the density and the more the amount of oxygen deficiency, the lower the L value. In a densified sintered body, the difference in the amount of oxygen deficiency can be confirmed based on the difference in the L value. In the sputtering of a high-mobility oxide semiconductor film, the margin of the film formation process conditions for obtaining a high-mobility film is narrow, and the mobility is likely to decrease due to crystallization outside the appropriate conditions. Therefore, if there is a distribution of oxygen deficiency in the plane of the target, it will affect the distribution of the mobility characteristics of film formation. In addition, if there is a distribution of the amount of oxygen deficiency in the thickness direction, there is a problem that the fixed film formation process conditions cannot be maintained during mass production, and as the quality of the target for mass production, the L* value must be uniform.

[0055] (Relative density) The density of the sintered body is obtained by the mercury Archimedes method or directly calculated from the size and weight.

[0056] (Crystal structure) The formation of the complex oxide in the pre-fired powder or the sintered oxide sintered body was confirmed by XRD: X-ray diffraction method.

[0057] An example of the apparatus and measurement conditions used in X-ray diffraction is shown below. X-ray diffractometer: RINT manufactured by Rigaku Corporation Scanning method: 2θ / θ method Target: Cu Tube voltage: 40 kV Tube current: 20 mA Scanning speed: 2.000° / min Sampling width: 0.050° Divergence slit: 1° Scattering slit: 1° Receiving slit: 0.3 mm

[0058] (Presence or absence of compositional deviation) The presence or absence of compositional deviation in the oxide sintered body was confirmed by SEM-EDX: Energy Dispersive X-ray Spectroscopy.

[0059] An example of the apparatus and measurement conditions used in compositional analysis is shown below. SEM-EDX: TM3030, Hitachi High-Technologies Corporation Acceleration voltage: 15 kV Detector element type: Silicon drift detector Element area: 30 mm 2 Energy resolution: 154 eV (Cu-Kα) Detectable elements: B5 - Am 95 Qualitative analysis: Automatic / Manual Quantitative analysis: Standardless method Examples

[0060] (Samples 1 - 31) Argon or oxygen was introduced into a magnetron sputtering apparatus, and one or more sputtering targets were used to fabricate an oxide semiconductor film having the composition shown in Table 1 below. Hall mobility, carrier concentration, etching rate for a specified etchant, crystallinity, and film composition were measured. These measurements were performed using an oxide semiconductor film formed on a glass substrate with a film thickness of 20 nm to 50 nm. In addition, for the measurement of film composition, a film formed on a silicon wafer was used. In addition, the target composition and the film composition were confirmed using a fluorescent X-ray analyzer (ZSX Primus; manufactured by Rigaku Corporation). The absolute values and compositional differences of the target composition and the film composition sometimes show some differences due to film formation conditions, the configuration of the film formation apparatus, measurement errors of the measuring instrument, or the like. In addition, an X-ray diffractometer (SmartLab; manufactured by Rigaku Corporation, 2θ / θ method) was used to confirm whether it was amorphous (non-crystalline). Three types of samples, namely, a sample that was not annealed after film formation, a sample that was annealed in air at 300°C, and a sample that was annealed in air at 400°C, were measured. If a broad pattern with no significant peaks (only a halo pattern) was observed, it was confirmed to be amorphous. If steep and significant peaks were observed, a part of it was confirmed to be crystalline. The results are shown in Table 1. The results confirmed to be amorphous by the X-ray diffractometer were regarded as amorphous, and amorphous was denoted as ○, while the results where a part of crystallinity was observed were denoted as △. The measurement results of Samples 1 to 4 in Table 1 are as Figure 6 shown. In addition, Figure 7 measurement examples of Samples 23 and 24 where a part of crystallinity was observed are shown.

[0061] In addition, the etching rate was measured using a sample that was not annealed after film formation, and ITO06 was used as the etchant. When the etching rate was 1.5 nm / s or more, it was denoted as ◎. When the etching rate was 1 nm / s or more, it was denoted as ○. When the etching rate was less than 1 nm / s, it was denoted as △.

[0062] Samples for Hall effect measurement were set in a Hall effect measurement instrument (HL5500PC; manufactured by ACCENT Corporation, ResiTest8400AC; manufactured by Tokuyo Technica Corporation), and the Hall effect was evaluated at room temperature to measure the carrier density and mobility. Specifically, electrodes were formed at the four corners of the sample, and a Hall effect measuring instrument was used to perform the measurement using the van der Pauw method. The above results are shown in Table 1.

[0063] [Table 1]

[0064] [Thin Film Semiconductor Devices 1-4] Using the oxide semiconductor thin films formed with the compositions of Samples 1-4 in Table 1, Figure 1 the thin film transistors shown were manufactured. A silicon oxide film (SiOx) with a thickness of 200 nm is formed on the substrate 10 as a buffer layer, and then an oxide semiconductor thin film with a thickness of 25 nm is formed as the active layer 11. After formation, it is patterned by the etching method using ITO06 and subjected to atmospheric annealing at 300 °C. The gate insulating film 12 is a silicon oxide film (SiOx) with a thickness of 100 nm. After formation, it is subjected to atmospheric annealing at 300 °C. As the gate electrode 13, a molybdenum film with a thickness of 200 nm is formed. The gate electrode 13 and the gate insulating film 12 are patterned by etching. After patterning, a plasma treatment is performed to impart conductivity to the oxide semiconductor layer. As the interlayer insulating film 14, a silicon oxide film (SiOx) with a thickness of 500 nm is formed. After formation, it is subjected to atmospheric annealing at 250 °C and patterned by etching. Then, as the source electrode 15S and the drain electrode 15D, a molybdenum film with a thickness of 300 nm is formed and patterned by etching.

[0065] A transistor is fabricated through the above process, and the characteristics (mobility, Vth, PBTS, NBTS) of the transistor are evaluated. The results are shown in Table 2 and Figures 8 - 11 as shown. In (a) of each figure, the initial characteristics are shown, in (b) PBTS is shown, and in (c) NBTS is shown. With Vd = 5 V and Vg variable in the range of -15 to +20 V, the mobility and Vth are measured. Vth is the threshold voltage, which is a value obtained from the transistor characteristics. PBTS (ΔVth) is the change in Vth after applying a gate voltage of +30 V for 60 minutes at a temperature of 60 °C compared to the Vth before application. NBTS (ΔVth) is the change in Vth after applying a gate voltage of -30 V for 60 minutes at a temperature of 60 °C compared to the Vth before application.

[0066] [Table 2]

[0067] (Thin film semiconductor devices 5, 6) The transistor characteristics (mobility, Vth) of the thin film semiconductor devices 5 and 6 with an oxide semiconductor thin film having the compositions of Samples 23 and 24 in Table 1 as the active layer are evaluated. The results are as Figure 12 shown. As the evaluation result of the thin film semiconductor device 5, the mobility is 15.8 cm 2 / V·s and Vth is +0.3 V. As the evaluation result of the thin film semiconductor device 6, the mobility is 23.9 cm 2 / V·s and Vth is +1.8 V.

[0068] From the above results, it was confirmed that for the transistor characteristics of the thin-film semiconductor devices 1 to 4, a high mobility of 25 cm 2 / V·s or more could be obtained. In addition, for the PBTS characteristics and NBTS characteristics, which are reliability indices for switching operations, good values of ΔVth ≤ 1 V were confirmed for both. On the other hand, in the composition where a part of the crystallinity was observed, the mobility was 25 cm 2 / Vs or less.

[0069] (Sputtering target Examples 1-5, Comparative Examples 1-3) According to the composition shown in Table 3 below, indium oxide, gallium oxide, germanium oxide, and zinc oxide were weighed and mixed using a ball mill. The mixed powder was dried and classified, and sintered in an oxygen atmosphere and an air atmosphere to obtain a sintered body.

[0070] Regarding the sintered body, the relative density and the SCI expressed by the L*a*b* color system were measured, and the results are shown in Table 3. In addition, the results of confirming the compositional deviation of the mixed particle powder and the oxide sintered body before and after sintering by EDX are also shown.

[0071] In Examples 1 to 5, using indium oxide, gallium oxide, germanium oxide, and zinc oxide as raw materials, sintering was performed in the air to obtain a sintered body having a relative density of 90% or more. When this sintered body was sintered particularly at 1350 °C or higher and 1600 °C or lower, it had a relative density of 98% or more, and the difference in the L value between the surface and the cross section was within ±3.

[0072] In Comparative Example 1, when firing was performed at 1650 °C or higher, due to the sublimation of zinc oxide, the weight decreased by about 7% before and after sintering, and a compositional deviation occurred.

[0073] In Comparative Examples 2 and 3, when sintering was performed at 1350 °C in an oxygen atmosphere, although the density was 98% or more, the difference in the L value between the surface and the center of the cross section was > 3. The L value is affected by the density and the oxygen deficiency of the oxide. The higher the density and the more the amount of oxygen deficiency, the lower the L value. Comparative Example 3 is a densified sintered body, so it can be confirmed from the L value that there is a difference in the amount of oxygen deficiency in the thickness direction. It should be noted that the relationship between the firing temperature, atmosphere, and chromaticity varies depending on the device and composition used. Therefore, even if the target is not produced under the conditions of the examples, as long as a target with uniform chromaticity can be obtained.

[0074] [Table 3]

[0075] Symbol Explanation 10 Substrate 11 Active Layer 11A Semiconductor Thin Film 11B Semiconductor Thin Film 12 Gate Insulating Film 12A Gate Insulating Layer 12B Gate Insulating Layer 13 Gate Electrode 13A Bottom Gate Electrode 13B Top Gate Electrode 14 Interlayer Insulating Film 15D Drain Electrode 15S Source Electrode 16 Etching Stop Layer 100, 100A to 100D Thin Film Transistors.

Claims

1. An oxide semiconductor thin film composed of an amorphous oxide semiconductor having In-Ga-Ge-Zn-O oxide containing indium, gallium, germanium and zinc as a main component, in, 70≤In≤90at%, 0<Ga≤10at%, 0<Ge≤10at%, 5≤Zn≤30at%.

2. The oxide semiconductor film according to claim 1, wherein the Hall mobility is 25 cm 2 / V·s or above.

3. The oxide semiconductor film according to claim 1, wherein the carrier density is 1.0×10 18 / cm 3 More than and less than 1.0×10 20 / cm 3 . 4 . The oxide semiconductor thin film according to claim 1 , wherein the etching rate of the oxide semiconductor thin film when etched with an oxalic acid-based etchant or a sulfuric acid / nitric acid-based etchant is 1 nm / sec or more.

5. The oxide semiconductor thin film according to claim 1, wherein 3≤Ga+Ge≤9.5at%.

6. The oxide semiconductor film according to claim 1 further contains at least one additional element selected from Si, Ti, Ni, Y, Ca, Al, Mg, Nb, Ta, Zr, Ba, Hf, W and Mo, and the total content of Ga, Ge and the additional elements is less than 10at%.

7. A thin film semiconductor device comprising: An active layer containing a high-mobility amorphous oxide semiconductor thin film, a gate electrode provided on at least one surface of the active layer via a gate insulating film, and a source electrode and a drain electrode connected to the active layer, in, The active layer includes the oxide semiconductor thin film according to any one of claims 1 to 6.

8. The thin film semiconductor device according to claim 7, wherein: The gate insulating film and the gate electrode are arranged on the upper surface of the active layer, the source electrode and the drain electrode are arranged on the upper surface side of the active layer, and a semiconductor thin film with a carrier density smaller than that of the active layer is sometimes provided on at least one of the upper and lower surfaces of the active layer.

9. The thin film semiconductor device according to claim 7, wherein: The gate insulating film and the gate electrode are arranged on the lower surface of the active layer, the source electrode and the drain electrode are arranged on the upper surface side of the active layer, and a semiconductor thin film with a carrier density smaller than that of the active layer is sometimes provided on at least one of the upper and lower surfaces of the active layer.

10. The thin film semiconductor device according to claim 9, wherein: An etching stop layer is provided on the upper surface of the active layer, and the source electrode and the drain electrode are provided on the etching stop layer on the upper surface side of the active layer.

11. The thin film semiconductor device according to claim 7, wherein: The gate insulating film and the gate electrode are arranged on both sides of the upper surface and the lower surface of the active layer, the source electrode and the drain electrode are arranged on the upper surface side of the active layer, and at least one side of the upper surface and the lower surface of the active layer sometimes has a semiconductor thin film with a carrier density smaller than that of the active layer.

12. The method for manufacturing a thin film semiconductor device according to claim 7, comprising: The step of forming the active layer by sputtering, The step of patterning the active layer by etching, and A step of annealing the active layer.

13. The method for manufacturing a thin film semiconductor device according to claim 8, comprising: The step of forming the active layer by sputtering, The step of patterning the active layer by etching, and A step of annealing the active layer.

14. A sputtering target for forming an oxide semiconductor thin film according to any one of claims 1 to 6, comprising an oxide sintered body mainly composed of an oxide In-Ga-Ge-Zn-O containing indium, gallium, germanium and zinc, in, 70≤In≤90at%、0<Ga≤10at%、0<Ge≤10at%、5≤Zn≤30at% The L* value of SCI expressed by the L*a*b* colorimetric system is distributed within ±3 in the thickness direction.

15. The sputtering target according to claim 14, which has a density of 98% or more.

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