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

Abstract

To provide an oxide semiconductor thin film having a low carrier concentration and a high hole mobility, and a thin film semiconductor device using the oxide semiconductor thin film as an active layer, in which a threshold voltage is not negatively shifted even at a high temperature, and to provide a sputtering target capable of forming the oxide semiconductor thin film, and a method for manufacturing the sputtering target.SOLUTION: The oxide semiconductor thin film is composed of an oxide semiconductor containing a prescribed oxide, and when the element ratio of the prescribed oxide is represented by GaXZnYZe, X is 0 to 0.8, Y is 0.2 to 0.8, Z is 0 to 0.3, and X+Y+Z=1.SELECTED DRAWING: Figure 1

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, a sputtering target for forming an oxide semiconductor thin film, and a method for manufacturing a sputtering target for forming an oxide semiconductor thin film. [Background technology]

[0002] Thin-film transistors (TFTs) that use an In-Ga-Zn-O-based oxide semiconductor film (IGZO) as the active layer can achieve higher mobility than TFTs that use a conventional amorphous silicon film as the active layer, and have therefore been widely applied to various displays in recent years (see, for example, Patent Document 1).

[0003] Recently, research into applying IGZO to semiconductor devices other than displays has been intensifying. However, negative shifts in threshold voltages have become an issue in device reliability tests (see Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-31750 [Non-patent literature]

[0005] [Non-Patent Document 1] A. Chasin et al., “Understanding and modeling the PBTI reliability of thin-film IGZO transistors,” vol. 1, pp. 31.1.1-31.1.4, 2022 [Non-patent document 2] J. Guo et al., “Compact Modeling of IGZO-based CAA-FETs with Time-zero-instability and BTI Impact on Device and Capacitor-less DRAM Retention Reliability,” Dig. Tech. Pap. - Symp. VLSI Technol., vol. 2022-June, pp. 300-301, 2022 Summary of the Invention [Problem to be solved by the invention]

[0006] Semiconductor devices require higher process temperatures than display devices, oxide semiconductors are more susceptible to reduction, and higher reliability is required than in display devices. Therefore, oxide semiconductor materials that do not experience a negative shift in threshold voltage even at high temperatures are required.

[0007] In view of the above circumstances, an object of the present invention is to provide an oxide semiconductor thin film that has a low carrier concentration and high hole mobility, and in which a thin film semiconductor device using the oxide semiconductor thin film as an active layer does not experience a negative shift in threshold voltage even at high temperatures, a thin film semiconductor device using the oxide semiconductor thin film, a method for manufacturing the same, and a sputtering target for forming an oxide semiconductor thin film that can form such an oxide semiconductor thin film, and a method for manufacturing the same. [Means for solving the problem]

[0008] As a result of extensive research conducted to achieve the above object, the inventors discovered that an oxide thin film containing gallium, germanium, and zinc maintains a low carrier concentration even after high-temperature processing, and the threshold voltage does not negatively shift, leading to the completion of the present invention. The present invention is as follows.

[0009] The first aspect of the present invention is an oxide semiconductor including a predetermined oxide, and the element ratio of the predetermined oxide is Ga. XZn Y Ge Z In this case, the oxide semiconductor thin film is in the range where X is 0 to 0.8, Y is 0.2 to 0.8, Z is 0 to 0.3, and X+Y+Z=1. A second aspect of the present invention is the oxide semiconductor thin film according to the first aspect, wherein the mobility is 1 cm 2 / V·s or more in oxide semiconductor thin films. A third aspect of the present invention is the oxide semiconductor thin film according to the first aspect, wherein the carrier concentration is 1×10 18 cm -3 The oxide semiconductor thin film is as follows: A fourth aspect of the present invention is the oxide semiconductor thin film according to the first aspect, further containing at least one element selected from Mg, Al, Zr, Hf, Ta, Y, W, and Ti. A fifth aspect of the present invention is a thin-film semiconductor device having a laminated structure of a gate electrode, a gate insulating film provided adjacent to the gate electrode, and an active layer made of an oxide semiconductor thin film provided adjacent to the gate insulating film, and further comprising a protective layer made of an insulating layer covering a part of the active layer, wherein a source electrode and a drain electrode are provided and connected to the active layer via the protective layer, and the active layer is made of the oxide semiconductor thin film according to any one of the first to fourth aspects. A sixth aspect of the present invention is the thin-film semiconductor device according to the fifth aspect, wherein the laminated structure of the gate electrode, the gate insulating film, and the active layer is provided on a substrate, and the protective layer is provided so as to cover the laminated structure and the gate insulating film. A seventh aspect of the present invention is a method for manufacturing a thin-film semiconductor device according to the fifth aspect, comprising the steps of forming the gate insulating film on the gate electrode, forming an active layer made of an oxide semiconductor thin film on the gate insulating film by a sputtering method, patterning the active layer, forming the insulating layer using the patterned active layer as a base film, patterning the insulating layer, forming a metal layer on the insulating layer, and patterning the metal layer to form the source electrode and the drain electrode. An eighth aspect of the present invention is a sputtering target for forming an oxide semiconductor thin film, which is made of an oxide sintered body containing a predetermined oxide, and the element ratio of the predetermined oxide is Ga. X Zn Y Ge Z In the sputtering target for forming an oxide semiconductor thin film, X is 0 to 0.8, Y is 0.2 to 0.8, Z is 0 to 0.3, and X+Y+Z=1. A ninth aspect of the present invention is the sputtering target for forming an oxide semiconductor thin film according to the eighth aspect, further containing at least one element selected from Mg, Al, Zr, Hf, Ta, Y, W, and Ti. A tenth aspect of the present invention is a sputtering target for forming an oxide semiconductor thin film according to the eighth or ninth aspect, which has a relative density of 95% or more. An eleventh aspect of the present invention is a method for producing a sputtering target for forming an oxide semiconductor thin film, which comprises pulverizing and mixing a gallium oxide powder, a zinc oxide powder, and a germanium oxide powder to obtain a mixed powder, forming a molded body using this mixed powder, and firing the molded body at 1100°C or higher and 1650°C or lower to produce a sputtering target composed of the oxide sintered body according to the eighth aspect. A twelfth aspect of the present invention resides in the method for producing a sputtering target for forming an oxide semiconductor thin film according to the eleventh aspect, wherein the mixed powder is pulverized and mixed so that the particle size distribution D90 of the mixed powder becomes less than 2.0 μm. A thirteenth aspect of the present invention resides in a method for producing a sputtering target for forming an oxide semiconductor thin film, comprising pulverizing and mixing gallium, zinc, and germanium as at least some of their oxides, hydroxides, or carbonates to obtain a mixed powder, pre-firing the mixed powder at 900°C or higher and 1400°C or lower to form a precursor powder, molding the precursor powder into a green body, and firing the green body at 1100°C or higher and 1650°C or lower to produce a sputtering target composed of the oxide sintered body according to claim 8. A fourteenth aspect of the present invention resides in the method for producing a sputtering target for forming an oxide semiconductor thin film according to the thirteenth aspect, wherein the mixed powder is pulverized and mixed so that the particle size distribution D90 of the mixed powder becomes less than 2.0 μm. [Effects of the Invention]

[0010] The present invention provides an oxide sintered body having a predetermined composition of gallium, germanium, and zinc, with a carrier concentration of 1×10 18 cm -3 The hole mobility is as low as 1 cm or less. 2 When this oxide semiconductor thin film is used as the active layer of a thin-film semiconductor device, it is possible to realize a thin-film semiconductor device in which the threshold voltage does not negatively shift even at high temperatures. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a ternary system diagram illustrating the composition of an oxide semiconductor according to the present invention. [Figure 2] This figure shows the range in which the mobility of a ternary composite oxide thin film of Ga, Ge, and Zn is 1 cm2 / V·s or more. [Figure 3] FIG. 1 is a diagram showing the range in which the carrier concentration of a ternary composite oxide thin film of Ga, Ge, and Zn is 1×10 18 cm −3 or less. [Figure 4] FIG. 1 is a diagram showing the range in which the etching rate of a ternary composite oxide thin film of Ga, Ge, and Zn with an oxalic acid-based etchant is 1 nm / sec or more. [Figure 5] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Figure 6] 1A to 1C are cross-sectional views illustrating a manufacturing process of an example of a semiconductor device structure of the present invention. [Figure 7] 1A to 1C are cross-sectional views illustrating a manufacturing process of an example of a semiconductor device structure of the present invention. [Figure 8] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Figure 9] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Figure 10] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Figure 11] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Figure 12] FIG. 10 is a diagram showing the transfer characteristics of the semiconductor device of the present invention. [Figure 13] FIG. 10 is a diagram showing the threshold voltage of a comparative semiconductor device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment 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 oxide semiconductor containing a predetermined oxide, and the element ratio of the predetermined oxide is Ga X Zn Y Ge Z In this case, X is in the range of 0 to 0.8, Y is in the range of 0.2 to 0.8, Z is in the range of 0 to 0.3, and X+Y+Z=1.

[0014] Such an oxide semiconductor thin film is amorphous and has a mobility of 1 cm 2 / V·s or more, carrier concentration is 1×10 18 cm -3 This is the range in which an etching rate of 1 nm / sec or more can be achieved with an oxalic acid etchant. This range is illustrated in FIGS. 1 to 4.

[0015] Figure 2 shows the mobility of a thin film of a ternary composite oxide of Ga, Ge, and Zn, with a mobility of 1 cm 2 Figure 3 shows the range of the carrier concentration of the ternary composite oxide thin film of Ga, Ge, and Zn above 1×10 18 cm -3 4 is a diagram showing the range in which the etching rate of a ternary composite oxide thin film of Ga, Ge and Zn with an oxalic acid-based etchant is 1 nm / sec or more.

[0016] FIG. 1 shows the combined range of FIGS. 2 to 4. X Ge Y Zn Z When X is 0 to 0.8, Y is 0.2 to 0.8, Z is 0 to 0.3, and X + Y + Z = 1, the mobility is 1 cm 2 / V·s or more, and the carrier concentration is 1×10 18 cm -3 This is a diagram showing the range below, and it was found that an etching rate of 1 nm / sec or more can be achieved with an oxalic acid-based etchant.

[0017] The oxide semiconductor thin film formed using such an oxide semiconductor has the above-mentioned carrier concentration and hole mobility. Therefore, in a semiconductor device using the oxide semiconductor thin film of the present invention as an active layer, that is, a semiconductor device having a gate electrode, a gate insulating film, an active layer, a source electrode, and a drain electrode such as a TFT, a reduction treatment is required to increase the carrier concentration. However, even after the reduction treatment, the carrier concentration is not more than 1×10 18 cm -3 It was also found that the following could be maintained:

[0018] Such reduction treatment does not need to be carried out specially for the purpose of reduction. After the oxide semiconductor thin film is formed, the reduction treatment of the oxide semiconductor thin film can be carried out simultaneously with a process at about 300°C or above 300°C, such as a CVD SiO film formation process.

[0019] The oxide semiconductor thin film of the present invention can be patterned by wet etching, and for example, when etched with an oxalic acid-based etchant, the etching rate is 1 nm / sec or more. Here, an example of the oxalic acid-based etchant is an etching solution containing 1 to 10% oxalic acid and 90% or more water. Of course, the oxide semiconductor thin film of the present invention may also be patterned by dry etching.

[0020] As mentioned above, the element ratio of the oxide in the oxide semiconductor thin film is Ga XZn Y Ge Z The present invention was completed based on the finding that, when X is 0 to 0.8, Y is 0.2 to 0.8, Z is 0 to 0.3, and X+Y+Z=1, a low carrier concentration is maintained even after a high-temperature process, and the threshold voltage does not negatively shift.

[0021] In particular, when X is in the range of 0.45 to 0.8, Y is in the range of 0.2 to 0.54, Z is in the range of 0 to 0.3, and X+Y+Z=1, the mobility and carrier concentration are in more preferable ranges.

[0022] The oxide semiconductor thin film of the present invention may further contain at least one element selected from Mg, Al, Zr, Hf, Ta, Y, W, and Ti. Ga X Zn Y Ge Z When the above-mentioned additive element is added to an oxide in which X is 0 to 0.8, Y is 0.2 to 0.8, Z is 0 to 0.3, preferably X is 0.45 to 0.8, Y is 0.2 to 0.54, Z is 0 to 0.3, and X+Y+Z=1, the mobility is 1 cm 2 / V·s or more, carrier concentration is 1×10 18 cm -3 The results of determining whether an etching rate of 1 nm / sec or more for an oxalic acid etchant can be achieved are shown in Table 1. In the table, those that can be achieved are marked with an O, and those that are outside the range are marked with an X.

[0023] As a result, the amounts of these additive elements are 15 at% or less for Mg and Al, 11 at% or less for Zr, 9 at% or less for Hf, 7 at% or less for Ta and Y, 6 at% or less for W, and 5 at% or less for Ti. Multiple types of these additive elements may be added as long as they are within the above-mentioned ranges, but if the mobility is less than 1 cm 2 / V·s or more, carrier concentration is 1×10 18 cm -3 It is necessary to add it in a range that can realize an etching rate of 1 nm / sec or more with respect to an oxalic acid-based etchant.

[0024] [Table 1]

[0025] The method for forming the oxide semiconductor thin film of the present invention is not particularly limited. For example, the film may be formed by sputtering using a sputtering target having the same composition as the film to be formed, or by atomic layer deposition (ALD) or vacuum evaporation.

[0026] The oxide semiconductor thin film of the present invention can also be used as an active layer of a thin film semiconductor device (also referred to as a thin film semiconductor device, or simply as a semiconductor device), which is a thin film semiconductor transistor such as a TFT.

[0027] A thin-film semiconductor device including the oxide semiconductor thin film of the present invention is a thin-film semiconductor device including an active layer made of an amorphous oxide semiconductor thin film, a gate electrode provided on one surface of the active layer via a gate insulating film, an insulating layer formed on the active layer, and a source electrode and a drain electrode provided via the insulating layer, wherein the active layer is made of the above-mentioned oxide semiconductor thin film of the present invention.

[0028] Specific thin-film semiconductor devices are not particularly limited to back-channel etch (BCE) types, etch-stop layer (ESL) types, etc., and examples include those having semiconductor thin films with low carrier concentrations on both the upper and lower surfaces of an active layer.

[0029] 5 shows a schematic configuration of a bottom-contact type thin-film semiconductor device as an example of the thin-film semiconductor device according to the present invention. Hereinafter, an etch-stop layer type (ESL) thin-film semiconductor device will be described as an example.

[0030] The thin film transistor 100 of this embodiment uses the oxide semiconductor thin film of the present invention as the active layer 11, and the active layer 11 is provided on a substrate 10 as a laminated structure of a gate insulating film 12 and a gate electrode 13, with the active layer 11 facing up. Specifically, the active layer 11, which is formed by patterning an oxide semiconductor thin film, is provided on a gate insulating film 12 provided so as to cover a gate electrode 13 formed by patterning a metal layer provided on the substrate 10. An insulating film 14 is provided to cover the active layer 11, and a source electrode 15S and a drain electrode 15D are provided, which are connected to the active layer 11 via the insulating film 14. A protective layer 16 is also provided to protect the source electrode 15S and the drain electrode 15D.

[0031] An example of a manufacturing process for the thin film transistor 100 will now be described with reference to FIGS. The substrate 10 is typically a Si substrate or a glass substrate, and a metal layer 13a that will become the gate electrode 13 is provided on the substrate 10 (FIG. 6(a)). The metal layer 13a is typically made of a metal single layer or multilayer film such as molybdenum (Mo), titanium (Ti), aluminum (Al), or copper (Cu), or a common gate electrode material used in semiconductor devices such as TiN, W, or WSi, and is formed by, for example, a sputtering method. In this embodiment, the gate electrode 13 is made of molybdenum. The thickness of the gate electrode 13 is not particularly limited and is, for example, 200 nm. The gate electrode 13 is formed by, for example, a sputtering method, an ALD method, or a vacuum deposition method. The metal layer 13a is patterned by etching to form the gate electrode 13 (FIG. 6(b)).

[0032] Thereafter, a gate insulating film 12 is provided so as to cover the gate electrode 13 (FIG. 6(c)). The gate insulating film 12 is formed between the gate electrode 13 and the active layer 11. The gate insulating film 12 is made of, for example, a silicon oxide film (SiOx), a silicon nitride film (SiNx), or a laminated film thereof. There are no particular limitations on the film formation method, and it may be a CVD method, a sputtering method, a vapor deposition method, or the like. There are no particular limitations on the film thickness of the gate insulating film 12, and it is, for example, 200 nm to 400 nm.

[0033] An oxide semiconductor thin film 11a that will become the active layer 11 is provided on the gate insulating film 12 (6(d)). The oxide semiconductor thin film 11a is made of the oxide semiconductor thin film of the present invention described above, and is formed by, for example, a sputtering method, an ALD method, a vacuum deposition method, or the like. In particular, it is preferably formed by a sputtering method.

[0034] The oxide semiconductor thin film 11a is patterned by wet etching or dry etching to form the active layer 11 (FIG. 7(a)). The oxide semiconductor thin film 11a of the present invention can achieve an etching rate of 1 nm / sec or more with an oxalic acid-based etchant, so it is particularly preferable to use wet etching, but of course dry etching can also be used without any problems.

[0035] The active layer 11 functions as a channel layer of the thin film transistor 100. The film thickness of the active layer 11 is, for example, 5 nm to 200 nm.

[0036] Next, an insulating film 14 is provided so as to cover the active layer 11 (FIG. 7(b)). The insulating film 14 is, for example, a silicon oxide (SiOx) film, and the method for forming the insulating film 14 is not particularly limited, and it may be formed using the same method as that for forming the gate insulating film 12.

[0037] The insulating film 14 is patterned to expose a part of the active layer 11, and then a source electrode 15S and a drain electrode 15D are provided thereon to complete the thin film transistor 100 (FIG. 7(c)).

[0038] The source electrode 15S and the drain electrode 15D are formed on the insulating film 14 and spaced apart from each other. The source electrode 15S and the drain electrode 15D can be formed of a single metal layer such as aluminum, molybdenum, copper, or titanium, or a multilayer film of these metals. As will be described later, the source electrode 15S and the drain electrode 15D can be simultaneously formed by patterning a metal film. The thickness of the metal film is, for example, 100 nm to 200 nm. The source electrode 15S and the drain electrode 15D are formed by, for example, sputtering, vacuum deposition, or the like.

[0039] At least one of the upper and lower surfaces of the active layer 11 of the thin film transistor 100 may be provided with a semiconductor thin film having a lower carrier concentration than the active layer 11 . An example of such a thin film transistor is shown in FIG.

[0040] 8 has semiconductor thin films 111 and 112 with low carrier concentrations on both the upper and lower surfaces of an active layer 11. Like the active layer 11, the semiconductor thin films 111 and 112 are formed by, for example, a sputtering method, an ALD method, or a vacuum deposition method.

[0041] The thin film transistor of the present invention is not limited to such a structure, and may have a structure as shown in FIGS.

[0042] The thin film transistor 110B in FIG. 9 has a structure in which a gate electrode 13 is provided on the underside of the active layer 11, and has a structure in which the gate electrode 13, gate insulating film 12, and active layer 11 are stacked on a substrate 10, and a source electrode 15S and a drain electrode 15D are drawn out from above the gate insulating film 12 and active layer 11.

[0043] The thin film transistor 110C in FIG. 10 has a structure in which an etching stop layer 17 is provided on the gate insulating film 12 and the active layer 11 of the thin film transistor 110B in FIG.

[0044] The thin film transistor 110D in FIG. 11 is a dual-gate type TFT, which 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 via an n-layer 11A provided continuously with the active layer 11, i.e., an N-type layer with a low concentration of N-type impurities.

[0045] Although the specific examples described above are lateral transistors, the present invention is not limited to these, and it goes without saying that vertical transistors may also be used.

[0046] In the above-described thin film semiconductor device, the oxide semiconductor thin film of the present invention having a predetermined composition of gallium, germanium, and zinc is used as the active layer, and therefore, the carrier concentration is 1×10 18 cm -3 The hole mobility is as low as 1 cm or less. 2 This has the effect of realizing an active layer with a threshold voltage of 1 / V·s or higher, thereby realizing a semiconductor device in which the threshold voltage does not negatively shift even at high temperatures.

[0047] [Sputtering target] Next, the sputtering target of this embodiment will be described.

[0048] The sputtering target may be a planar target or a cylindrical rotary target. The sputtering target has the same composition as that of the oxide semiconductor thin film of the present invention, and the element ratio of the oxide is Ga. X Zn Y Ge Z In this case, X is in the range of 0 to 0.8, Y is in the range of 0.2 to 0.8, Z is in the range of 0 to 0.3, and X+Y+Z=1, and preferably X is in the range of 0.45 to 0.8, Y is in the range of 0.2 to 0.54, Z is in the range of 0 to 0.3, and X+Y+Z=1.

[0049] Furthermore, the sintered body of the sputtering target of the present invention can further contain at least one element selected from Mg, Al, Zr, Hf, Ta, Y, W, and Ti, similarly to the oxide semiconductor thin film, for the reasons described above.

[0050] Since the sputtering target of the present invention contains an oxide whose powder particles are difficult to pulverize, such as gallium oxide, depending on the pulverization and mixing processes, the uniformity of the composition of the oxide sintered body may not be ensured, resulting in a low density and the possibility of uneven composition when formed into an oxide semiconductor thin film. Therefore, the manufacturing process, particularly the pulverization and mixing processes, must be carefully controlled. The relative density of the oxide sintered body of the sputtering target of the present invention must be 95% or more, and there must be no unevenness in composition or density. Since compositional variations and density variations are observed as minute spots on the sintered body, it is necessary to carefully inspect the sintered body to ensure that there are no spots compared to a normal sintered body.

[0051] (Method for manufacturing sputtering targets) The method for producing the sputtering target of the present invention is not particularly limited as long as it is a method that can produce an oxide sintered body having the above composition, and the following two production methods can be exemplified.

[0052] The first method is a method of producing a sputtering target having an oxide sintered body by mixing gallium oxide powder, zinc oxide powder, and germanium oxide powder to form a molded body, and then 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 achieve the element ratio of the target oxide sintered body described above.

[0053] The second method is a method for producing a sputtering target having an oxide sintered body by mixing at least a portion of gallium, zinc, and germanium as oxides, hydroxides, or carbonates, calcining the resulting precursor powder at 900° C. to 1400° C., molding the resulting precursor powder into a compact, and then calcining the compact at 1100° C. to 1650° C. Here, the phrase "at least a portion of gallium, zinc, and germanium" means that some of the elements may be calcined as elements, and the remaining elements may be blended as oxides, etc. The weight ratio of the raw material powders is determined so as to achieve the element ratio of the target oxide sintered body described above.

[0054] The second method will be further exemplified below to explain the production method in detail. In this embodiment, the raw material powder is granulated by a spray drying method, which can perform drying and granulation at the same time. The addition of a binder eliminates the need for a pulverization process, which is difficult to pulverize, and allows the use of spherical powder with good flowability, making it easier to achieve a uniform composition distribution in the sputtering target.

[0055] In particular, compositions with a high Ga2O3 content tend to be non-uniform during pulverization and mixing, making it difficult for the powder particles to be pulverized. Simply checking the average particle size is insufficient to determine whether pulverization and mixing are sufficient; this can result in a low-density sintered body and concerns about uneven composition and density. Therefore, to ensure that pulverization and mixing are sufficient, it is preferable to measure the particle size distribution and manage it using the D90 value, as described below. Details will be given later, but by controlling the particle size distribution at D90, it is possible to produce a sintered body without spots.

[0056] The raw material powder contains at least oxides, hydroxides, or carbonates of gallium, zinc, and germanium. In addition, one or more powders selected from the oxides of the above-mentioned additive elements may be mixed. Furthermore, a dispersant or the like may be added to the raw material powder mixture.

[0057] A ball mill can be used to grind and mix the raw material powders, but other media-agitating mills, such as bead mills and rod mills, can also be used. The surfaces of the balls or beads that serve as the agitating media may be coated with a resin, which effectively prevents impurities from being mixed into the powder. In particular, the preferred pulverization and mixing method is wet ball mill pulverization, which can pulverize and mix the powder particles uniformly.

[0058] The mixed powder is pre-fired at a temperature between 900°C and 1400°C. If the firing temperature is below 900°C, the pre-fire is insufficient and the composite oxide is not fully formed, while if the temperature exceeds 1400°C, sintering proceeds during pre-fire and the particle size of the primary particles increases, preventing the sintered density from increasing in the subsequent firing. The calcined powder is again wet-pulverized in a ball mill or the like together with a dispersant, a binder, etc., and granulated by spray drying.

[0059] The average particle size of the granulated powder is set to 500 μm or less. If the average particle size of the granulated powder exceeds 500 μm, cracks and breakages in the compact become prominent, and granular dots appear on the surface of the sintered body. If such a sintered body is used as a sputtering target, it may cause abnormal discharge or particle generation.

[0060] The average particle size of the granulated powder is more preferably 20 μm or more and 100 μm or less. This reduces the volume change (compressibility) before and after CIP (Cold Isostatic Press) molding, suppresses cracking in the molded body, and enables stable production of long molded bodies. However, if the average particle size is less than 20 μm, the powder tends to fly up, making handling difficult.

[0061] Here, the term "average particle size" refers to the cumulative percentage of particle size distribution measured using a sieving particle size distribution analyzer at 50%. The average particle size is measured using a "Robot Sifter RPS-105M" manufactured by Seishin Enterprise Co., Ltd.

[0062] The granulated powder is 100 MPa / cm 2 The molding is performed at a pressure of 100 MPa or more. This allows for the production of a sintered body with a relative density of 95% or more. If the molding pressure is less than 100 MPa, the molded body will be fragile and difficult to handle, and the relative density of the sintered body will decrease.

[0063] The molding method used is the CIP method. The CIP form can be a typical vertical loading type vertical method, but a horizontal loading type horizontal method is preferable. This is because if a long plate-shaped compact is produced using a vertical CIP, the thickness will vary due to the powder shifting in the mold, and the compact may break under its own weight during handling.

[0064] The compact is then fired at a temperature of 1100°C or higher and 1650°C or lower to form a sintered body. If the firing temperature is below 1100°C, the conductivity and relative density will be low, making it unsuitable for use as a target. On the other hand, if the firing temperature exceeds 1650°C, some components will evaporate, causing compositional deviation and a decrease in relative density in the fired body, and the strength of the fired body will decrease due to coarsening of the crystal grains.

[0065] The compact is fired in air or an oxidizing atmosphere, which allows the desired oxide sintered body to be produced stably.

[0066] To produce granulated powder, powders with an average primary particle size of 0.3 μm or more and 1.5 μm or less are used. This shortens the mixing and grinding time and improves the dispersion of the raw material powders within the granulated powder.

[0067] The angle of repose of the granulated powder is preferably 32° or less, which increases the fluidity of the granulated powder and improves the moldability and sinterability.

[0068] (Processing process) The sintered body produced as described above is machined into a plate shape of desired shape, size, and thickness to produce a sputtering target made of a Ga-Ge-Zn-O based sintered body. The sputtering target is brazed to a backing plate.

[0069] According to this embodiment, it is possible to produce a long sputtering target with a longitudinal length exceeding 1000 mm. This allows the production of a large sputtering target without a divided structure, which prevents deterioration of film properties that can occur when bonding material (soldering agent) penetrates into the gaps (seams) between the divided parts and is sputtered, enabling stable film formation. In addition, it is less likely that particles will be generated due to redeposition (re-deposition) of sputtered particles that have accumulated in the gaps.

[0070] [Sputtering target evaluation] (relative density) The density of the sintered body was determined by the mercury Archimedes method or by direct calculation from the dimensions and weight.

[0071] (crystal structure) The generation of composite oxides in the calcined powder or sintered oxide sintered body was confirmed by XRD (X-ray diffraction).

[0072] An example of the apparatus and measurement conditions used for X-ray diffraction is as follows: X-ray diffraction equipment: Rigaku Corporation RINT Scanning method: 2θ / θ method Target: Cu Tube voltage: 40kV Tube current: 20mA Scan speed: 2,000° / min Sampling width: 0.050° Divergence slit: 1° Scattering slit: 1° Receiving slit: 0.3 mm

[0073] (crystal structure) The generation of the composite oxide in the oxide sintered body and whether the oxide semiconductor thin film was amorphous were confirmed by XRD (X-ray diffraction).

[0074] An example of the apparatus and measurement conditions used for X-ray diffraction is as follows: X-ray diffraction equipment: Rigaku Corporation RINT Scanning method: 2θ / θ method Target: Cu Tube voltage: 40kV Tube current: 20mA Scan speed: 2,000° / min Sampling width: 0.050° Divergence slit: 1° Scattering slit: 1° Receiving slit: 0.3 mm

[0075] (composition) The composition of the oxide sintered body was confirmed by SEM-EDX: energy dispersive X-ray spectroscopy.

[0076] An example of the apparatus and measurement conditions used in the composition analysis is as follows: SEM-EDX: TM3030 Hitachi High-Technologies Corporation Accelerating voltage: 15 kV Detector type: Silicon drift detector Element area: 30mm 2 Energy resolution: 154 eV (Cu-Kα) Detectable elements: B5~Am 95 Qualitative analysis: Auto / Manual Quantitative analysis: standardless method

[0077] Regarding the particle size distribution measurement during ball mill pulverization, D90 was measured using a particle size distribution analyzer. An example of the apparatus and measurement conditions used in measuring particle size distribution is as follows. Particle size distribution analyzer: MT3300EXII Microtrac Bell Co., Ltd. Measurement principle: Laser diffraction and scattering method Measurement range: 0.02 to 2000 μm Light source: 3 x 780nm 3mW Class 1 semiconductor lasers Required sample size: 0.05 to 2 g Ultrasonic output: 30W Ultrasonic time: 180s Organic solvents: Available Optical axis adjustment, focus adjustment: Auto [Example]

[0078] (target) (Examples 1-5) Gallium oxide, zinc oxide, and germanium oxide were weighed out so as to have the compositions of Examples 1 to 5 in Table 2 below, and sintered in the air to obtain sintered bodies. The relative density and resistivity of the sintered body were measured, and the results are shown in Table 2.

[0079] In the examples, gallium oxide, germanium oxide, and zinc oxide were used as raw materials, and powder particles were obtained by pulverizing them to a particle size distribution D90≦1.2 μm. By sintering them in air, sintered bodies with a relative density of 95% or more were obtained.

[0080] (Comparative Examples 1-9) In Comparative Example 1, the composition had a high Ga content and a high content of gallium oxide, which is difficult to pulverize, and the particle size distribution D90 of the powder was ≧2.0 μm, so the relative density was less than 95% and spots were observed. In Comparative Examples 2 and 3, the content of GeO2, which has a low melting point, was high, and during sintering, it melted before the density increased, so the relative density was less than 95%. In Comparative Example 4, the content of ZnO, which is easily sublimated, was high, and the relative density decreased due to sublimation during sintering, resulting in a relative density of less than 95%. In Comparative Examples 5 to 8, when the sintering temperature was less than 1000°C, sintering did not proceed sufficiently and the relative density was less than 95%. When fired at a temperature exceeding 1650°C, the relative density decreased due to sublimation, and the relative density was less than 95%. Comparative Example 9 was obtained by sintering a material with the same composition as Examples 2 and 4, but with a particle size distribution D90 of 2.0 μm or greater. The relative density was 97.2%, but fine spots were observed in the sintered body. These spots were due to compositional and density variations, and were found to affect the distribution of properties of the sputtered oxide semiconductor thin film.

[0081] [Table 2]

[0082] (oxide semiconductor thin film) Examples 11-15 Using targets manufactured in the same manner as in the above-described Examples with the compositions shown in Table 3, oxide semiconductor thin films of Examples 11-15 and Comparative Examples 11-13 were formed by sputtering, and the hole mobility and carrier concentration after the SiOx film formation by CVD were measured.

[0083] Specifically, a 100 nm SiO film was formed by CVD on a 50 nm oxide semiconductor thin film formed on a glass substrate, and then the substrate was cut into a 7 mm square and the four corners were etched using a dry etching device to prepare a sample for measuring the Hall effect.

[0084] The sample for Hall effect measurement was set in a resistivity / Hall measurement system (ResiTest8400AC; manufactured by Toyo Corporation), and the Hall effect was evaluated at room temperature, and the carrier concentration and mobility were measured. The results are shown in Table 3.

[0085] (Comparative Examples 11-13) In Comparative Example 11, a ZnGeO (27:73) target was used, in Comparative Example 12 a GaZnO (40:60) target was used, and in Comparative Example 13 a GaZnGeO (87:10:3) target was used to produce oxide thin films by sputtering.

[0086] The oxide semiconductor thin films of Examples 11 to 15 were amorphous and had a mobility of 1 cm 2 / V·s or more, carrier concentration is 1×10 18cm -3 The etching rate for the oxalic acid etchant was 1 nm / sec or more.

[0087] In contrast, in Comparative Examples 11 and 13, the thin film was an insulator, and the mobility and carrier concentration could not be measured. 2 / V·s or more, but the carrier concentration was 1×10 18 cm -3 It was neither less nor amorphous.

[0088] [Table 3]

[0089] (thin film transistor) 12 and 13 show a comparison of the characteristics of a TFT using the oxide semiconductor thin film of the present invention as the active layer (having the structure of FIG. 5) and the characteristics of a TFT using IGZO as the active layer. 12 shows the characteristics of a TFT in which the active layer is the oxide semiconductor thin film of GaZnGe (61:36:3) of Example 13. On the other hand, FIG. 13 shows the characteristics of a TFT in which the active layer is IGZO. As a result, it was found that in a TFT using IGZO, Vth shifts negatively, but in a TFT using the GaZnGe oxide semiconductor thin film of the present invention as the active layer, Vth does not shift negatively. [Explanation of symbols]

[0090] 10 Substrate 11 Active layer 12 Gate insulating film 12A, 12B Gate insulating layer 13 Gate electrode 13A Bottom gate electrode 13B Top gate electrode 14 insulating film 15D Drain electrode 15S Source Electrode 16 Protective film 17 Etching stop layer 100, 110A-110D Thin-film transistors 111, 112 Semiconductor thin films

Claims

1. composed of an oxide semiconductor containing a predetermined oxide, The element ratio of the predetermined oxide is Ga Ｘ Zn Ｙ Ge Ｚ where X is 0 to 0.8, Y is 0.2 to 0.8, Z is 0 to 0.3, and X+Y+Z=1. Oxide semiconductor thin film.

2. The oxide semiconductor thin film according to claim 1 , Mobility is 1 cm ２ / V·s or more Oxide semiconductor thin film.

3. The oxide semiconductor thin film according to claim 1 , Carrier concentration is 1×10 １８ cm －３ is Oxide semiconductor thin film.

4. The oxide semiconductor thin film according to claim 1 , Further containing at least one element selected from Mg, Al, Zr, Hf, Ta, Y, W and Ti. Oxide semiconductor thin film.

5. a gate electrode, a gate insulating film provided adjacent to the gate electrode, and an active layer made of an oxide semiconductor thin film provided adjacent to the gate insulating film; and a protective layer made of an insulating layer covering a part of the active layer; and a source electrode and a drain electrode connected to the active layer via the protective layer; The active layer is made of the oxide semiconductor thin film according to any one of claims 1 to 4. Thin film semiconductor devices.

6. 6. The thin-film semiconductor device according to claim 5, the laminated structure of the gate electrode, the gate insulating film, and the active layer is provided on a substrate, and the protective layer is provided so as to cover the laminated structure and the gate insulating film; Thin film semiconductor devices.

7. 6. The method for manufacturing a thin-film semiconductor device according to claim 5, forming the gate insulating film on the gate electrode; forming an active layer made of an oxide semiconductor thin film on the gate insulating film by a sputtering method; patterning the active layer; The insulating layer is formed using the patterned active layer as a base film, and after patterning the insulating layer, a metal layer is formed on the insulating layer, and the source electrode and the drain electrode are formed by patterning the metal layer. A method for manufacturing a thin film semiconductor device.

8. A sputtering target for forming an oxide semiconductor thin film, comprising: It is composed of an oxide sintered body containing a predetermined oxide, The element ratio of the predetermined oxide is Ga Ｘ Zn Ｙ Ge Ｚ where X is 0 to 0.8, Y is 0.2 to 0.8, Z is 0 to 0.3, and X+Y+Z=1. Sputtering target for forming oxide semiconductor thin films.

9. The sputtering target for forming an oxide semiconductor thin film according to claim 8, Further containing at least one element selected from Mg, Al, Zr, Hf, Ta, Y, W and Ti. Sputtering target for forming oxide semiconductor thin films.

10. The sputtering target for forming an oxide semiconductor thin film according to claim 8 or 9, Relative density is 95% or more Sputtering target for forming oxide semiconductor thin films.

11. A sputtering target comprising the oxide sintered body according to claim 8 is manufactured by crushing and mixing gallium oxide powder, zinc oxide powder, and germanium oxide powder to obtain a mixed powder, forming a compact using this mixed powder, and firing the compact at 1100°C or higher and 1650°C or lower. A method for producing a sputtering target for forming an oxide semiconductor thin film.

12. The mixed powder is pulverized and mixed so that the particle size distribution D90 is less than 2.0 μm. A method for producing the sputtering target for forming an oxide semiconductor thin film according to claim 11.

13. A sputtering target comprising the oxide sintered body according to claim 8 is manufactured by crushing and mixing at least a portion of gallium, zinc, and germanium as oxides, hydroxides, or carbonates to obtain a mixed powder, calcining the mixed powder at 900°C or higher and 1400°C or lower to form a precursor powder, molding the precursor powder into a compact, and calcining the compact at 1100°C or higher and 1650°C or lower. A method for producing a sputtering target for forming an oxide semiconductor thin film.

14. The mixed powder is pulverized and mixed so that the particle size distribution D90 is less than 2.0 μm. A method for producing the sputtering target for forming an oxide semiconductor thin film according to claim 13.

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