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

Abstract

To provide an oxide semiconductor thin film capable of realizing a high mobility active layer thin film transistor and a thin film semiconductor device using the same, as well as a sputtering target capable of forming the above-described oxide semiconductor thin film and a method for manufacturing the same.SOLUTION: An oxide semiconductor thin film comprises an amorphous oxide semiconductor mainly composed of an In-Ga-Ge-Zn-O oxide comprising indium, gallium, germanium, and zinc, with 70≤In≤90at%, 0<Ga≤10at%, 0<Ge≤10at%, 5≤Zn≤30at%.SELECTED DRAWING: None

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) using an In-Ga-Zn-O-based oxide semiconductor film (IGZO) as an active layer can obtain high mobility as compared with a conventional TFT using an amorphous silicon film as an active layer. Therefore, in recent years, it has been widely applied to various displays (see, for example, 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 requirements for higher resolution, lower power consumption, and higher frame rate in various displays, the demand for oxide semiconductors with higher mobility has been increasing. However, in a thin film transistor using IGZO as an active layer, it has been difficult to exceed 10 cm 2 / Vs in mobility. In addition, with the spread of current-driven devices, oxide semiconductors with high mobility are required. However, with the increase in mobility, there are problems such as variations in characteristics due to crystallization of the film, processability problems, and TFT malfunction due to high mobility and high carrier density.

[0005] For example, Patent Document 4 discloses that the electron carrier concentration is 10 18 / cm 3When the above oxide is used for the channel layer of a TFT, it has been found that the on / off ratio cannot be obtained sufficiently and it is not suitable for a normally-off type TFT. An amorphous oxide containing microcrystals and having an electron carrier concentration of less than 10 18 / cm 3 has been proposed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

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 capable of realizing a thin film transistor with a high-mobility active layer, a thin film semiconductor device using the same, and a method for manufacturing the same. Another object is to provide a sputtering target capable of forming the above-described oxide semiconductor thin film and a method for manufacturing the same.

Means for Solving the Problems

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

[0009] A first aspect of the present invention is an amorphous oxide semiconductor composed mainly of an oxide of In-Ga-Ge-Zn-O consisting of indium, gallium, germanium, and zinc, and is an oxide semiconductor thin film with 70 ≦ In ≦ 90 at%, 0 < Ga ≦ 10 at%, 0 < Ge ≦ 10 at%, and 5 ≦ Zn ≦ 30 at%. A second aspect of the present invention is the oxide semiconductor thin film of the first aspect having a hole mobility of 25 cm 2 / V·s or more. A 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 A 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. A fifth aspect of the present invention is the oxide semiconductor thin film of the first aspect with 3 ≦ Ga + Ge ≦ 9.5 at%. A sixth aspect of the present invention is the oxide semiconductor thin film of the first aspect further containing at least one additive element selected from Si, Ti, Ni, Y, Ca, Al, Mg, Nb, Ta, Zr, Ba, Hf, W, and Mo, and having a total content of Ga, Ge, and the additive element of 10 at% or less. A seventh aspect of the present invention is a thin-film semiconductor device including an active layer made of 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 is made of the oxide semiconductor thin film of any one of the first aspect to the sixth aspect. ​The eighth aspect of the present invention is the thin-film semiconductor device according to the seventh aspect, in which 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 of the active layer, and at least one of the upper surface and the lower surface of the active layer may include a semiconductor thin film having a carrier density smaller than that of the active layer. The ninth aspect of the present invention is the thin-film semiconductor device according to the seventh aspect, in which 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 of the active layer, and at least one of the upper surface and the lower surface of the active layer may include a semiconductor thin film having a carrier density smaller than that of the active layer. The tenth aspect of the present invention is the thin-film semiconductor device according to the ninth aspect, in which 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. The eleventh aspect of the present invention is the thin-film semiconductor device according to the seventh aspect, in which the gate insulating film and the gate electrode are provided on both sides of 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 at least one of the upper surface and the lower surface of the active layer may include a semiconductor thin film having a carrier density smaller than that of the active layer. The twelfth aspect of the present invention is a method for manufacturing a thin-film semiconductor device according to the seventh aspect, the method including a step of forming the active layer by a sputtering method, a step of patterning the active layer by etching, and a step of annealing the active layer. The thirteenth aspect of the present invention is a method for manufacturing a thin-film semiconductor device according to any one of the eighth to eleventh aspects, the method including a step of forming the active layer by a sputtering method, 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 thin film according to any one of the 1st to 6th aspects, which is composed of an oxide sintered body mainly composed of an In-Ga-Ge-Zn-O oxide composed of indium, gallium, germanium, and zinc. The 15th aspect of the present invention is the sputtering target according to the 14th aspect, having a density of 98% or more. The 16th aspect of the present invention is the sputtering target according to the 14th aspect, where 70 ≦ In ≦ 90 at%, 0 < Ga ≦ 10 at%, 0 < Ge ≦ 10 at%, 5 ≦ Zn ≦ 30 at%, and the L* value of SCI shown in the L*a*b* color system has a distribution within ±3 in the thickness direction.

Advantages of the Invention

[0010] Such a present invention is composed of indium, gallium, germanium, and zinc, and by using an oxide semiconductor mainly composed of an In-Ga-Ge-Zn-O oxide with a predetermined composition, an oxide semiconductor film with an electron carrier density of 1 × 10 18 / cm 3 or more and less than 1 × 10 20 / cm 3 and a single-film Hall mobility of 25 cm 2 / V·s or more can be realized, in which the crystallinity is suppressed, the processability is excellent, and the oxide semiconductor film can be stably driven by TFT.

Brief Description of the Drawings

[0011]

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Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments 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-O composed of indium, gallium, germanium, and zinc, and 70 ≦ In ≦ 90 at%, 0 < Ga ≦ 10 at%, 0 < Ge ≦ 10 at%, 5 ≦ Zn ≦ 30 at%. In is the main element that increases mobility, and Zn is an element that increases mobility. Ga and Ge are elements that decrease mobility, but it is difficult to decrease mobility compared to other elements. That is, in the present invention, Ge is added to a typical IGZO (In-Ga-Zn-O)-based composition as a high-mobility oxide semiconductor material to obtain a predetermined composition, so that the electron carrier density is 1 × 10 18 / cm 3 or more and less than 1 × 10 20 / cm 3 and the Hall mobility of the single film is 25 cm 2It becomes an amorphous film with a high mobility film of 0 / V·s or more and the crystallinity suppressed, and has excellent processability and can be stably driven by TFT.

[0014] As described above, the contents of Ga and Ge are 0 < Ga ≦ 10 at% and 0 < Ge ≦ 10 at%, but preferably 3 ≦ Ga + Ge ≦ 9.5 at%, more preferably 3.5 ≦ Ga + Ge ≦ 7.0 at%, and still more preferably 3.5 ≦ Ga + Ge ≦ 6.0 at%. By setting the contents of Ga and Ge as described above, a predetermined mobility and carrier density can be achieved. That is, in the range of 3 ≦ Ga + Ge ≦ 9.5 at%, the hole mobility is 25 cm 2 / V·s or more, and the carrier density is 1×10 18 ~5×10 19 / cm 3 and in the range of 3.5 ≦ Ga + Ge ≦ 7.0 at%, the hole mobility is 30 cm 2 / V·s or more, and the carrier density is 5×10 18 ~5×10 19 / cm 3 and in the range of 3.5 ≦ Ga + Ge ≦ 6.0 at%, the hole mobility is 33 cm 2 / V·s or more, and the carrier density is 7×10 18 ~5×10 19 / cm 3 and it becomes. If the contents of Ga and Ge are more than this, the film will have a small mobility. Such an oxide semiconductor thin film of the present invention has a hole mobility of 25 cm 2 / V·s or more after annealing in air at about 300 °C, preferably 30 cm 2 / V·s or more, and particularly preferably 33 cm 2 / V·s or more.

[0015] In addition, the carrier density after annealing in air 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 5.0×10 19 / cm3 is less than. The oxide semiconductor thin film of the present invention has a band gap Eg of 2.4 eV or more and 2.8 eV or less. The oxide semiconductor thin film of the present invention can be etched at an etching rate of 1 nm / sec or more with any one of, for example, ITO06N·07N (manufactured by Kanto Chemical Co., Inc.) which is an oxalic acid-based etchant, a mixed acid-based etchant such as sulfuric acid·nitric acid, or other etchants. The oxide semiconductor thin film of the present invention may contain other elements as long as it does not inhibit the characteristics of the oxide of In-Ga-Ge-Zn-O described above. Examples of such additive elements include at least one element selected from Si, Ti, Ni, Y, Ca, Al, Mg, Nb, Ta, Zr, Ba, Hf, W, and Mo, and can be contained within a range that does not inhibit the above-described characteristics. These additive elements have the property that although the degree of reducing the mobility is large compared to Ga and Ge, it is difficult to reduce the mobility compared to other elements. That is, even when these additive elements are added at 10 at% or less, for example, they have the property of not significantly reducing the mobility. 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. Although Sb and Sn also have the property of being difficult to reduce the mobility similar to Ga and Ge, they are preferably not contained in the present invention because good characteristics cannot be obtained with respect to processability, crystallinity, and stability of TFT characteristics.

[0016] The method for forming the oxide semiconductor thin film of the present invention is not particularly limited. For example, it may be formed by sputtering using a sputtering target having the same composition as the composition to be formed, or may 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] Further, the oxide semiconductor thin film of the present invention can be used as an active layer of a thin film semiconductor device (device) such as a thin film semiconductor transistor such as a TFT. The thin-film semiconductor device including the oxide semiconductor thin film of the present invention includes an active layer made of an amorphous oxide semiconductor thin film with high mobility, 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, and is a thin-film semiconductor device in which the active layer is made of the oxide semiconductor thin film of the present invention described above. That is, the oxide semiconductor thin film is used, for example, as an active layer with high mobility in a thin-film transistor such as a so-called top-gate type field-effect transistor, and may be a type of semiconductor device including a semiconductor thin film having a carrier density smaller than that of the active layer on at least one of the upper and lower portions of the active layer. Further, it can also be applied as an active layer of a field-effect transistor having an etching stop layer (ESL) structure, a back-channel etching (BCE) structure, or a dual gate (DoubleGate) structure.

[0018] A specific example of the thin-film semiconductor device may have a structure in which the gate insulating film and the gate electrode are provided on the upper surface of the active layer, and the source electrode and the drain electrode are provided on the upper surface side of the active layer. FIG. 1 shows the structure of an example of such a thin-film semiconductor device.

[0019] FIG. 1 shows a schematic configuration of an example of the thin-film transistor according to 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 drawn 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 with a buffer layer formed thereon. 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, for example, by sputtering. In this 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, for example, by sputtering, ALD method, vacuum evaporation method, etc.

[0021] The active layer 11 functions 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, for example, by 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 laminated film thereof. The film forming method is not particularly limited, and may 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 laminated film thereof. The film forming method is not particularly limited, and may 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 metal film such as aluminum, molybdenum, copper, titanium, or a multilayer film of these metals. As will be described later, the source electrode 15S and the drain electrode 15D can be formed simultaneously by patterning a 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, a sputtering method, a vacuum evaporation method, or the like.

[0025] 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 and lower surfaces of the active layer 11 of the thin film transistor 100. An example of such a thin film transistor is shown in FIG. 2. The thin film transistor 100A in FIG. 2 has semiconductor thin films 11A and 11B having a small carrier density on both the lower and upper surfaces of the active layer 11. As the semiconductor thin films 11A and 11B, for example, In-Ga-Zn-based materials can be used, and the carrier density is 1.0×10 15 / cm 3 ~1.0×10 18 / cm 3 The thin films can be mentioned, but it is not limited to the In-Ga-Zn system. Further, the semiconductor thin films 11A and 11B are formed by, for example, a sputtering method, an ALD method, a vacuum evaporation method, or the like, in the same manner as the active layer 11.

[0026] The thin film transistor of the present invention is not limited to such a structure, and a thin film transistor having a structure as shown in FIGS. 3 to 5 may also be used. The thin film transistor 100B in FIG. 3 has a structure in which the gate electrode 13 is provided on the lower surface of 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 drawn out from above the gate insulating film 12 and the active layer 11. The thin film transistor 100C in FIG. 4 has a structure in which an etching stop layer 16 is provided on the gate insulating film 12 and the active layer 11 of the thin film transistor 100B in FIG. 3. The etching stop layer 16 is formed of, for example, a silicon oxide film (SiOx), and the film formation method is not particularly limited, and may be a CVD method, a sputtering method, an evaporation method, or the like. The film thickness of the etching stop layer 16 is not particularly limited, and is, for example, 50 nm to 300 nm.

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

[0028] Also in the structures of FIGS. 3 to 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 and lower surfaces of the active layer 11. Note that the above-described specific examples illustrate horizontal transistors, but the present invention is not limited thereto, and it goes without saying that vertical transistors may also be used.

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

[0030] The sputtering target may be a planar target or a cylindrical rotary target. The sputtering target is made of an oxide sintered body containing In, Ga, Ge, and Zn, and the composition ratio is the same as that of the oxide semiconductor thin film described above, and the preferred composition ratio is also the same, so redundant description will be 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 an oxide containing 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 can 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 so that the L* value of SCI shown in the L*a*b* color system has a distribution within ±3 in the thickness direction. Such a color distribution indicates whether sintering has been performed evenly. The oxide of the element composition of the present invention is likely to have uneven sintering, and it is necessary to average the sintering by adjusting the composition and flow rate of the atmosphere gas, etc. The average property of the color distribution is required both in the in-plane direction and in the thickness direction. However, since unevenness is likely to occur particularly in the thickness direction distribution, the L* value of SCI in the thickness direction is defined. The L* value of SCI in the in-plane direction also has a distribution within ±3. However, since this varies depending on the situation of the sintering apparatus, it is necessary to adjust appropriately, but the point is to finally evaluate with the L* value of SCI shown in the L*a*b* color system.

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

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

[0036] (Method for manufacturing sputtering target) The method for manufacturing the sputtering target of the present invention is not particularly limited as long as it is a method for obtaining 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 1100°C or higher and 1650°C or lower. The weight ratio of the raw material powders is determined so as to be the element ratio of the above-described oxide sintered body as the target.

[0038] Further, the second method is a method for manufacturing a sputtering target having an oxide sintered body by mixing indium, zinc, gallium, and germanium as at least a part of oxides, hydroxides, or carbonates, molding a precursor powder calcined at 900°C to 1400°C into a molded body, and firing the molded body at 1100°C or higher and 1650°C or lower. Here, at least a part of indium, zinc, gallium, and germanium means that a part may be calcined as an element and the remaining elements may be blended as oxides or the like. Note that the weight ratio of the raw material powders is determined so as to be the element ratio of the above-described oxide sintered body as the target.

[0039] Hereinafter, the second method will be further exemplified to explain the manufacturing method in detail. In this embodiment, the raw material powder is granulated by a spray drying method capable of performing drying and granulation at once. By adding a binder, the need for a pulverization operation with poor pulverizability is eliminated, and spherical powders with good fluidity can be used, etc., making it easier for the composition distribution of the sputtering target to become uniform.

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

[0041] As a method for pulverizing and mixing the raw material powder, a ball mill may be used, but in addition to the ball mill, other medium stirring mills such as a bead mill and a rod mill can also be used. A resin coat or the like may be applied to the surface of the balls or beads serving as the stirring medium. Thereby, the incorporation of impurities into the powder is effectively suppressed.

[0042] The mixed granular powder is calcined at a temperature of 900°C or higher and 1400°C or lower. When the calcination temperature is less than 900°C, the calcination is insufficient and the composite oxide is not completely formed. When it exceeds 1400°C, sintering progresses during the calcination and the grain shape of the primary particles becomes large, so the sintering density does not increase in the subsequent full sintering. The calcined powder is wet pulverized again with a dispersant, a binder, etc. using a ball mill or the like, and granulated by spray drying.

[0043] The average particle size of the granulated powder is set to 500 μm or less. When the average particle size of the granulated powder exceeds 500 μm, cracks and fractures in the molded body become prominent, and granular spots appear on the surface of the fired body. Using such a fired body as a sputtering target may cause abnormal discharge or particle generation.

[0044] The more preferable average particle diameter of the granulated powder is 20 μm or more and 100 μm or less. Thereby, the change in volume (compression ratio) before and after CIP (Cold Isostatic Press) molding is small, crack generation in the molded body is suppressed, and a long molded body is stably produced. When the average particle diameter is less than 20 μm, the powder is likely to fly up and handling becomes difficult.

[0045] Here, the "average particle diameter" means the value at which the cumulative percentage of the particle size distribution measured by a sieve classification type particle size distribution measuring instrument is 50%. As the value of the average particle diameter, the measured value by "Robot Sifter RPS-105M" manufactured by Seishin Enterprise Co., Ltd. is used.

[0046] The granulated powder is molded at 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 molding pressure is less than 100 MPa, the molded body is likely to break, handling is difficult, and the relative density of the sintered body decreases.

[0047] As the molding method, the CIP method is adopted. The form of CIP may be a typical vertical load type vertical method, and preferably, a horizontal load type horizontal method is desirable. This is because when a long plate-shaped molded body is manufactured by vertical CIP, variations in thickness occur due to displacement of the powder in the mold, or it breaks under its own weight during handling.

[0048] Further, the molded body is fired at 1100 °C to 1650 °C to be made into a sintered body. When the firing temperature is less than 1100 °C, the conductivity and relative density become low, and it becomes unsuitable for the target application. On the other hand, when the firing temperature exceeds 1650 °C, evaporation of some components occurs, composition deviation of the fired body occurs, or the strength of the fired body decreases due to coarsening of crystal grains.

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

[0050] For the production of granulated powder, powders with an average particle diameter of primary particles of 0.3 μm or more and 1.5 μm or less are used respectively. This enables shortening of the mixing and pulverization time and improves the dispersibility of the raw material powder in the granulated powder.

[0051] The angle of repose of the granulated powder is preferably 32° or less. This enhances the fluidity of the granulated powder and improves the formability and sinterability.

[0052] (Processing step) The fired body produced as described above is machined into a plate shape with a desired shape, size, and thickness to produce a sputtering target made of an In-Ga-Ge-Zn-O-based sintered body. The sputtering target is brazed to a backing plate.

[0053] According to this embodiment, a long sputtering target with a length in the longitudinal direction exceeding 1000 mm can be produced. As a result, a large sputtering target without a divided structure can be produced, preventing deterioration of film characteristics that may occur due to sputtering of the bonding material (brazing material) that has entered the gap (joint) of the divided part, and enabling stable film formation. In addition, it becomes difficult for particles caused by reattachment (redeposition) of sputtered particles deposited in the above gap to occur.

[0054] [Evaluation of sputtering target] (L* value of SCI shown in the L*a*b* color system) The L* value was measured using a Konica Minolta spectrophotometer CM-700d in the SCI value (measurement method including regular reflection light). The measurement was performed at the center of the Target surface and cross-section. The L value is affected by density and oxygen deficiency of the oxide. The higher the density and the larger 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 from the difference in the L value. In the sputtering of a high-mobility oxide semiconductor film, the margin of the film-forming process conditions for obtaining a high-mobility film is narrow, and outside the appropriate conditions, the mobility is likely to decrease due to crystallization. Therefore, if there is a distribution of oxygen deficiencies in the plane of the target, it will affect the distribution of the mobility characteristics of the formed film. Also, if there is a distribution of the amount of oxygen deficiencies in the thickness direction, there is a problem that production cannot be carried out while maintaining certain film-forming process conditions during mass production, and it is necessary that the L* value be uniform as the quality of the target for mass production.

[0055] (Relative density) The density of the sintered body was determined by the mercury Archimedes method or directly calculated from the dimensions and weight.

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

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

[0058] (Presence or absence of composition deviation) The presence or absence of composition 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 the composition analysis is as follows. SEM-EDX: TM3030 manufactured by 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: Auto / Manual Quantitative analysis: Standardless method

Example

[0060] (Sample 1 - 31) Argon gas and oxygen gas were introduced into a magnetron sputtering apparatus, and an oxide semiconductor thin film having the composition shown in Table 1 below was manufactured using one sputtering target or a plurality of sputtering targets. Hall mobility, carrier concentration, etching rate with respect to a predetermined 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. For the measurement of the film composition, a film formed on a silicon wafer was used. In addition, the target composition and the film composition were confirmed by a fluorescent X-ray analyzer (ZSX Primus; manufactured by Rigaku). The absolute values and compositional differences between the target composition and the film composition may cause slight differences due to film formation conditions, film formation apparatus configuration, measurement errors of the measuring instrument, etc. In addition, it was confirmed whether it was amorphous by an X-ray diffractometer (SmartLab; manufactured by Rigaku, 2θ / θ method). Measurements were performed on three types of samples: a sample not annealed after film formation, a sample annealed in air at 300 °C, and a sample annealed in air at 400 °C. When a broad pattern with no significant peaks (only a halo pattern) was observed, it was regarded as amorphous, and when a sharp and significant peak was observed, it was regarded as having partially expressed crystallinity. The results are shown in Table 1. The results of confirming whether it was amorphous by the X-ray diffractometer were regarded as crystallinity, with amorphous marked as ○ and those with partially expressed crystallinity marked as △. The measurement results of Samples 1 to 4 in Table 1 are shown in Fig. 6. In addition, measurement examples of Samples 23 and 24 with partially expressed crystallinity are shown in Fig. 7.

[0061] Also, for the etching rate, samples that were not annealed after film formation were used, and ITO06 was used as the etchant. When the etching rate was 1.5 nm / s or more, it was marked as ◎; when it was 1 nm / s or more, it was marked as ○; and when it was less than 1 nm / s, it was marked as △.

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

[0063]

Table 1

[0064] [Thin film semiconductor device 1-4] Using the oxide semiconductor thin film formed with the composition of Samples 1-4 in Table 1, the thin film transistor shown in FIG. 1 was manufactured. A silicon oxide film (SiOx) with a thickness of 200 nm was formed as a buffer layer on the substrate 10, and then an oxide semiconductor thin film with a thickness of 25 nm was formed as the active layer 11. After formation, it was patterned by etching with ITO06 and subjected to air annealing at 300°C. The gate insulating film 12 was formed with a silicon oxide film (SiOx) having a thickness of 100 nm. After formation, it was subjected to air annealing at 300°C, and a molybdenum film with a thickness of 200 nm was formed as the gate electrode 13. The gate electrode 13 and the gate insulating film 12 were patterned by etching, and after patterning, plasma treatment was performed to impart conductivity to the oxide semiconductor layer. An insulating film 14 with a thickness of 500 nm of silicon oxide film (SiOx) was formed. After formation, annealing was performed at 250 °C in air, and patterning was carried out by etching. Then, as the source electrode 15S and the drain electrode 15D, a molybdenum film with a thickness of 300 nm was formed and patterned by etching.

[0065] Transistors were fabricated in the above process, and transistor characteristics (mobility, Vth, PBTS, NBTS) were evaluated. The results are shown in Table 2 and Figures 8 to 11. (a) in each figure shows the initial characteristics, (b) shows PBTS, and (c) shows NBTS. With Vd at 5 V, Vg was varied in the range of -15 to +20 V to measure the mobility and Vth. Vth is the threshold voltage and is a value obtained from transistor characteristics. PBTS (ΔVth) was defined as 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) was defined as 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 thin film semiconductor devices 5 and 6 with oxide semiconductor thin films having the compositions of Samples 23 and 24 in Table 1 as the active layer were evaluated. The results are shown in Figure 12. As a result of the evaluation of thin film semiconductor device 5, the mobility was 15.8 cm 2 / V·s and Vth was +0.3 V. As a result of the evaluation of thin film semiconductor device 6, the mobility was 23.9 cm 2 / V·s and Vth was +1.8 V.

[0068] From the above results, in the transistor characteristics of thin film semiconductor devices 1 to 4, the mobility was 25 cm 2It was confirmed that a high mobility of 1 / V·s or more was obtained. Also, for both the PBTS characteristics and the NBTS characteristics, which are indicators of the reliability of the switching operation, it was confirmed that ΔVth ≤ 1 V, which is a good value. On the other hand, in the composition where some crystallinity was observed, the mobility became 25 cm 2 / Vs or less.

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

[0070] Table 3 shows the results of measuring the relative density and the SCI shown in the L*a*b* color system for the sintered body. Furthermore, the results of confirming the presence or absence of compositional deviation before and after sintering between the mixed granular powder and the oxide sintered body by EDX are also shown.

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

[0072] In Comparative Example 1, when fired at 1650 °C or more, there was a weight loss of about 7% before and after sintering due to the sublimation of zinc oxide, and a compositional deviation occurred.

[0073] In Comparative Examples 2 and 3, when sintered at 1350 °C in an oxygen atmosphere, the density was 98% or more, but 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 oxygen deficiency amount, the lower the L value. Since Comparative Example 3 is a densified sintered body, it can be confirmed from the L value that there is a difference in the oxygen deficiency amount in the thickness direction. Note that since the relationship among the firing temperature, atmosphere, and chromaticity varies depending on the devices and compositions used, it is not always necessary to fabricate the Target under the conditions of the examples, as long as a Target with uniform chromaticity can be obtained.

[0074]

Table 3

Explanation of Symbols

[0075] 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~100D Thin film transistor

Claims

1. An amorphous oxide semiconductor composed mainly of an oxide of In—Ga—Ge—Zn—O composed of indium, gallium, germanium, and zinc, An oxide semiconductor thin film having 70≦In≦90 at%, 0<Ga≦10 at%, 0<Ge≦10 at%, and 5≦Zn≦30 at%.

2. The hole mobility is 25 cm ２ / V·s or more The oxide semiconductor thin film according to Claim 1.

3. The carrier density is 1.0×10 １８ / cm ３ or more and less than 1.0×10 ２０ / cm ３ ​ The oxide semiconductor thin film according to Claim 1.

4. The etching rate when etched with an oxalic acid-based etchant or a sulfuric acid / nitric acid-based etchant is 1 nm / sec or more The oxide semiconductor thin film according to Claim 1.

5. Ga + Ge is 3≦Ga + Ge≦9.5 at% The oxide semiconductor thin film according to Claim 1.

6. Further containing 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, The oxide semiconductor thin film according to Claim 1.

7. An active layer composed of 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, A thin film semiconductor device including a source electrode and a drain electrode connected to the active layer, wherein The active layer is made of the oxide semiconductor thin film according to any one of Claims 1 to 6 Thin film semiconductor device.

8. 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 of the active layer, and at least one of the upper and lower surfaces of the active layer may be provided with a semiconductor thin film having a carrier density smaller than that of the active layer, The thin film semiconductor device according to Claim 7.

9. 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 of the active layer, and at least one of the upper and lower surfaces of the active layer may be provided with a semiconductor thin film having a carrier density smaller than that of the active layer, The thin film semiconductor device according to Claim 7.

10. 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 The thin film semiconductor device according to Claim 9.

11. The gate insulating film and the gate electrode are provided on both sides of the upper and lower surfaces of the active layer, the source electrode and the drain electrode are provided on the upper surface side of the active layer, and at least one of the upper and lower surfaces of the active layer may include a semiconductor thin film having a carrier density smaller than that of the active layer. The thin film semiconductor device according to claim 7.

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

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

14. A sputtering target for forming an oxide semiconductor thin film according to any one of claims 1 to 6, which is composed of an oxide sintered body mainly composed of an oxide of In—Ga—Ge—Zn—O composed of indium, gallium, germanium, and zinc. A sputtering target.

15. having a density of 98% or more, the sputtering target according to claim 14.

16. where 70≦In≦90 at%, 0<Ga≦10 at%, 0<Ge≦10 at%, 5≦Zn≦30 at%, and the L* value of SCI shown in the L*a*b* color system has a distribution within ±3 in the thickness direction. the sputtering target according to claim 14.

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