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

Abstract

To provide an oxide semiconductor thin film having a low carrier concentration and high hole mobility, in which a thin-film semiconductor device using the oxide semiconductor thin film as an active layer does not exhibit a negative shift in threshold voltage even at high temperatures, a semiconductor device using the oxide semiconductor thin film, a sputtering target capable of forming such an oxide semiconductor thin film, and a method for manufacturing the same.SOLUTION: An oxide semiconductor thin film is composed of an oxide semiconductor mainly composed of an oxide containing indium, gallium, and aluminum in the following composition, and the composition ratios of X, Y, and Z of the oxide semiconductor are the composition ratios of a region surrounded by a line segment connecting points A and B, a line segment connecting points B and C, a line segment connecting points C and D, and a line segment connecting points D and A in a ternary phase diagram of In, Ga, and Al. The composition: InXGaYAlZ. The point A: In10Ga90Al0. The point B: In30Ga30Al40. The point C: In45Ga15Al40. The point D: In45Ga55Al0.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Thin-film transistors (TFTs) that use an In-Ga-Zn-O 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 therefore have 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 become active. However, a negative shift in threshold voltage during device reliability testing has become an issue (see Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-31750 A [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] In semiconductor devices, the process temperature is higher than in display devices, oxide semiconductors are more easily reduced, and higher reliability is required than in display devices. Therefore, oxide semiconductor materials that do not undergo 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 having a low carrier concentration and high hole mobility, which is an active layer of a thin film semiconductor device that does not exhibit a negative shift in threshold voltage even at high temperatures, a semiconductor device using the same, a sputtering target capable of forming 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, it was discovered that an oxide semiconductor thin film containing indium, gallium, and aluminum in a predetermined composition ratio maintains a low carrier concentration even after high-temperature processing and does not experience a negative shift in threshold voltage, thereby completing the present invention. The present invention is as follows.

[0009] A first aspect of the present invention is an oxide semiconductor thin film composed of an oxide semiconductor mainly composed of an oxide containing indium, gallium, and aluminum in the following composition, wherein the oxide semiconductor has a composition ratio in a region surrounded by a line segment connecting points A and B, a line segment connecting points B and C, a line segment connecting points C and D, and a line segment connecting points D and A in a ternary phase diagram of In, Ga, and Al: Composition: In X Ga Y Al Z Point A: In 10 Ga 90 Al0 Point B: In 30 Ga 30 Al 40 Point C: In 45 Ga 15 Al 40 Point D: In 45 Ga 55 Al0 The second aspect of the present invention is a semiconductor device having a carrier concentration of 1×10 18 cm -3 The oxide semiconductor thin film according to a first aspect is as follows. The third aspect of the present invention is a semiconductor device having a Hall mobility of 1 cm 2 / Vs or more. A fourth aspect of the present invention is the oxide semiconductor thin film according to the first aspect, which has an etching rate of 1 nm / sec or more when etched with a phosphoric acid-based etchant. A fifth aspect of the present invention is a semiconductor device comprising an oxide semiconductor thin film, at least a part of which is the oxide semiconductor thin film according to any one of the first to fourth aspects. A sixth aspect of the present invention is a semiconductor device according to the fifth aspect, which has a gate electrode, a gate insulating film, an active layer, a source electrode and a drain electrode, and the oxide semiconductor thin film is the active layer. A seventh aspect of the present invention is a method for manufacturing a semiconductor device including an oxide semiconductor thin film, the method comprising: forming the oxide semiconductor thin film according to any one of the first to fourth aspects as at least a part of the oxide semiconductor thin film; and performing a reduction treatment of an oxide semiconductor in the oxide semiconductor thin film. An eighth aspect of the present invention is a sputtering target composed of an oxide sintered body mainly composed of an oxide containing indium, gallium, and aluminum in the following composition, wherein the oxide semiconductor has a composition ratio in a region surrounded by a line segment connecting points A and B, a line segment connecting points B and C, a line segment connecting points C and D, and a line segment connecting points D and A in a ternary phase diagram of In, Ga, and Al. Composition: In X Ga Y Al Z Point A: In 10 Ga 90 Al0 Point B: In 30 Ga 30 Al 40 Point C: In 45 Ga 15 Al 40 Point D: In 45 Ga 55 Al0 A ninth aspect of the present invention is the sputtering target according to the eighth aspect, wherein the sputtering target has a relative density of 90% or more. A tenth aspect of the present invention is a method for producing a sputtering target having the oxide sintered body according to the eighth or ninth aspect, by mixing indium oxide powder, gallium oxide powder, and aluminum oxide powder to form a molded body, and sintering the molded body at 1100°C or higher and 1650°C or lower. An eleventh aspect of the present invention is a method for producing a sputtering target, comprising mixing oxides, hydroxides or carbonates of indium, gallium, and aluminum and calcining the resulting precursor powder at 1000°C to 1500°C to form a green body, and calcining the green body at 1100°C or higher and 1650°C or lower to produce a sputtering target having the oxide sintered body according to the eighth or ninth aspect. Effect of the Invention

[0010] In the present invention, an oxide sintered body having a predetermined composition of indium, gallium, and aluminum has a carrier concentration of 1×10 18 cm -3 The hole mobility is as low as 1 cm 2 By using this as the active layer of a semiconductor device, a semiconductor device can be realized in which the threshold voltage does not negatively shift even at high temperatures. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a ternary diagram showing the composition of an oxide semiconductor of the present invention. [Diagram 2] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Diagram 3] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Figure 4] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Diagram 5] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Figure 6] 1 is a cross-sectional view showing an example of the structure of a semiconductor device of the present invention. [Figure 7] 13 is a diagram showing the transfer characteristics of a semiconductor device 8. FIG. [Figure 8] FIG. 13 is a diagram showing the threshold voltage of a comparative semiconductor device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 mainly composed of an oxide containing indium, gallium, and aluminum in the following composition, and the oxide semiconductor has a composition ratio in a region surrounded by a line segment connecting points A and B, a line segment connecting points B and C, a line segment connecting points C and D, and a line segment connecting points D and A in a ternary phase diagram of In, Ga, and Al. Composition: In X Ga Y Al Z Point A: In 10 Ga 90 Al0 Point B: In 30 Ga 30 Al 40 Point C: In 45 Ga 15 Al 40 Point D: In 45 Ga 55 Al0

[0014] This composition range is shown in FIG. In-containing oxides are prone to oxygen vacancies, and if In exceeds 45%, the carrier concentration becomes too high at high temperatures, making it unusable. On the other hand, Ga and Al suppress the occurrence of oxygen vacancies, but if Al exceeds 40%, the carrier concentration is too low and electrical conductivity cannot be obtained, making it unusable. Also, in regions with high concentrations of both Ga and Al, electrical conductivity is difficult to obtain, making it unusable.

[0015] In the composition range enclosed by the lines connecting points A, B, C, and D, the carrier concentration is 1×10 18 cm -3 The hole mobility is as low as 1 cm 2 It was found that the oxide semiconductor thin film had a capacitance of 1000 Ω / Vs or higher.

[0016] 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 having the oxide semiconductor thin film of the present invention as an active layer, i.e., 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 less than 1×10 18 cm -3 It was also found that the following could be maintained:

[0017] Such a 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 by a process at about 300° C. or above 300° C., such as a SiO film formation process by CVD.

[0018] The oxide semiconductor thin film of the present invention can be patterned by wet etching, and has an etching rate of 1 nm / sec or more when etched with, for example, a phosphoric acid-based etchant, such as a PAN-based etching solution containing 70-80% phosphoric acid, 1-9% nitric acid, and 1-10% acetic acid.

[0019] A preferred range of the oxide semiconductor of the present invention is shown in the ternary diagram of FIG. As shown in this ternary diagram, the oxide semiconductor in the area surrounded by points P, Q, R, and S below has a hole mobility of 2 cm 2 / Vs or more, and the carrier concentration is 5×10 16 cm -3 This is a more preferable composition range in which a relatively high mobility can be maintained. Point P: In 15 Ga 85 Al0 Q point:In 30 Ga 45 Al 25 R point: In 45 Ga 35 Al 25 S point: In40 Ga 60 Al0

[0020] 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 composition of the film to be formed, or by atomic layer deposition (ALD) or vacuum deposition, and the film formation method is not particularly limited as long as an amorphous oxide semiconductor thin film can be formed.

[0021] The oxide semiconductor thin film of the present invention can also be used as an active layer of a thin film semiconductor device (also simply called a semiconductor device), which is a thin film semiconductor transistor such as a TFT.

[0022] 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, 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 the present invention described above.

[0023] A specific example of a semiconductor device has 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. An example of the structure of such a thin film semiconductor device is shown in FIG.

[0024] FIG. 2 shows a schematic configuration of one example of a thin film transistor according to the present invention. The thin film transistor 110 of this embodiment comprises an active layer 11, a gate insulating film 12, a gate electrode 13, and a protective film (passivation) 14 on a substrate 10, and has a source electrode 15S and a drain electrode 15D extended from the active layer 11 via the protective film 14.

[0025] The substrate 10 is typically a Si substrate or a glass substrate. The gate electrode 13 is typically made of a metal single layer or multilayer film such as molybdenum (Mo), titanium (Ti), aluminum (Al), copper (Cu), or a general 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, a vacuum deposition method, or the like.

[0026] The active layer 11 functions as a channel layer of the thin film transistor 110. The active layer 11 has a thickness of, for example, 5 nm to 200 nm. The active layer 11 is made of the oxide semiconductor thin film of the present invention described above. The active layer 11 is formed by, for example, a sputtering method, an ALD method, a vacuum deposition method, or the like.

[0027] 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 of these. The film formation method is not particularly limited, and may be a CVD method, a sputtering method, a vapor deposition method, or the like. The thickness of the gate insulating film 12 is not particularly limited, and is, for example, 200 nm to 400 nm.

[0028] The source electrode 15S and the drain electrode 15D are formed on the protective film 14 and the cap layer 13, spaced apart from each other. The source electrode 15S and the drain electrode 15D can be made of a single metal layer such as aluminum, molybdenum, copper, titanium, or a multi-layer film of these metals. As 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, a sputtering method, a vacuum deposition method, or the like.

[0029] At least one of the upper and lower surfaces of the active layer 11 of the thin film transistor 110 may be provided with a semiconductor thin film having a lower carrier density than the active layer 11 .

[0030] An example of such a thin film transistor is shown in FIG. A thin film transistor 110A in FIG. 3 has semiconductor thin films 11A and 11B, each having a low carrier density, on both the upper and lower surfaces of an active layer 11. The semiconductor thin films 11A and 11B may be, for example, InGaAl oxide (IGA) films having a high carrier concentration. Similarly to the active layer 11, the semiconductor thin films 11A and 11B are formed by, for example, a sputtering method, an ALD method, a vacuum deposition method, or the like.

[0031] The thin film transistor of the present invention is not limited to such a structure, and may have a structure as shown in FIGS.

[0032] The thin-film transistor 110B in FIG. 4 has a structure in which a gate electrode 13 is provided on the lower surface of an active layer 11, and has a structure in which the gate electrode 13, a gate insulating film 12, and an active layer 11 are laminated 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 the active layer 11.

[0033] The thin-film transistor 110C in FIG. 5 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 110B in FIG.

[0034] The thin-film transistor 110D in FIG. 6 is a dual-gate type TFT, and has a bottom gate electrode 13A on the lower surface side of the active layer 11 via a gate insulating layer 12A, and a top gate electrode 13B on the upper surface side via a gate insulating layer 12B. 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.

[0035] 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.

[0036] [Semiconductor Devices 1-16] Using various oxide semiconductor thin films having the compositions shown in the table below, ESL-type thin film transistors having an etching stop layer (ESL) as shown in Figure 6 were manufactured. The oxide semiconductor thin films were used as active layers.

[0037] The oxide semiconductor thin films with the compositions shown in the table below were formed using In2O3, Ga2O3, and Al2O3 sputtering targets, and In-Ga-Al-O thin films of various compositions were deposited using a multi-cathode.

[0038] The ESL type semiconductor device of FIG. 5 was manufactured by the following procedure. First, a Mo layer was formed as a gate electrode metal on the substrate 10 and patterned to form the gate electrode 13 .

[0039] Next, as the gate insulating film 13, a laminated film of SiO (upper) / SiN (lower) was formed.

[0040] Next, as described above, active layers 11 made of oxide semiconductor thin films of various compositions (samples 1-16 in Table 1) were formed, annealed at 400° C., and patterned by wet etching using a phosphoric acid-based etchant.

[0041] Next, SiOx was deposited by CVD as an ESL to serve as an etching stop layer 16. In this CVD deposition process, the substrate was heated to about 300° C., and the oxide semiconductor forming the active layer 11 was reduced by this process.

[0042] After that, the etching stop layer 16 was patterned, a Ti film was formed as a metal film for the source and drain and patterned, then a protective film (passivation) 14 was formed and annealed, and then the protective film 14 was patterned, and finally a source electrode 15S and a drain electrode 15D were formed.

[0043] (Sample 1-17) For Sample 1-17 having the composition in Table 1, the hole mobility and carrier concentration were measured after the SiOx film was formed by CVD.

[0044] Specifically, a 100 nm thick SiO film was formed by CVD on a 50 nm thick oxide semiconductor 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.

[0045] 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 density and mobility were measured. The results are shown in Table 1.

[0046] As a result, the oxide semiconductor thin films of Samples 1, 2, 5 to 11, and 15 had a carrier concentration of 1×10 18 cm -3 The hole mobility is as low as 1 cm 2 / Vs or more. In particular, the oxide semiconductor thin films of Samples 1, 5, and 7 to 11 were found to be particularly preferable. On the other hand, samples 3 and 4 are insulators, and samples 12 and 14 have a Hall mobility of 1 cm 2 / Vs, and sample 13 has a carrier concentration of 1×10 18 cm -3 were larger and less favorable.

[0047] [Table 1]

[0048] (Semiconductor Device 8) The transfer characteristics showing the relationship between the gate voltage and the drain current were measured for the semiconductor device 8 having the structure of FIG. 6 in which the oxide semiconductor thin film of sample 8 is used as the active layer. The temperature at which the gate insulating layer 12B made of SiO was formed on the active layer 11 by CVD was set to 300°C. The threshold voltage (gate voltage when the drain current becomes 1 nA) was measured at four points, A to D. As shown in Fig. 7, the threshold voltage was -0.5 to 3 V in all cases, and it was confirmed that there was no negative shift.

[0049] (Comparative semiconductor device) A similar device was created and the threshold voltage was measured, except that the active layer was IGZO111 (In:Ga:Zn=33.3:33.3:33.3) and the CVD film formation temperature was lowered to 270°C. As a result, as shown in Figure 8, the device was in a normally-on state with no switching operation, and the threshold voltage could not be measured.

[0050] From the results of FIGS. 7 and 8, it was found that the semiconductor device using the oxide semiconductor of the present invention did not experience a negative shift in threshold voltage even when subjected to high-temperature treatment, and had excellent heat resistance.

[0051] (Sputtering target) Indium oxide, gallium oxide, and aluminum oxide were weighed and mixed using a ball mill to obtain the composition of Sample 8 in Table 1. The mixed powder was sintered by holding it at 1000°C for 10 hours in air to obtain a sintered body.

[0052] In the examples, indium oxide, gallium oxide, and aluminum oxide were used as raw materials, and a sintered body with a relative density of 96.4% was obtained by sintering in air. Although this sintered body is an insulator, it is possible to form the oxide semiconductor thin film of the present invention by RF sputtering. [Explanation of symbols]

[0053] 10 Substrate 11 Active layer 11A,B Semiconductor thin film 12 Gate insulating film 12A Gate Insulation Layer 12B Gate insulation layer 13 Gate electrode 13A Bottom gate electrode 13B Top gate electrode 14 Protective film 15D Drain electrode 15S Source Electrode 16 Etching stop layer 110 Thin-film transistor

Claims

1. The oxide semiconductor includes an oxide containing indium, gallium, and aluminum in the following composition as a main component, The composition ratios of X, Y, and Z of the oxide semiconductor are the composition ratios of a region surrounded by a line segment connecting points A and B, a line segment connecting points B and C, a line segment connecting points C and D, and a line segment connecting points D and A in a ternary phase diagram of In, Ga, and Al. Oxide semiconductor thin film. Composition: In Ｘ G Ｙ A Ｚ Point A: In １０ Ga ９0 Al ０ Point B: In ３０ Ga ３０ Al ４０ Point C: In ４５ Ga １５ Al ４０ Point D: In ４５ Ga ５５ Al ０

2. Carrier concentration is 1×10 １８ cm －３ Is less than or equal to The oxide semiconductor thin film according to claim 1 .

3. Hall mobility is 1 cm ２ / Vs or more The oxide semiconductor thin film according to claim 1 .

4. The etching rate when etched with a phosphoric acid-based etchant is 1 nm / sec or more. The oxide semiconductor thin film according to claim 1 .

5. A semiconductor device comprising an oxide semiconductor thin film, At least a part of the oxide semiconductor thin film is the oxide semiconductor thin film according to any one of claims 1 to 4. Semiconductor device.

6. 6. The semiconductor device according to claim 5, comprising a gate electrode, a gate insulating film, an active layer, a source electrode and a drain electrode, and the oxide semiconductor thin film is the active layer.

7. 1. A method for manufacturing a semiconductor device having an oxide semiconductor thin film, comprising the steps of: forming an oxide semiconductor thin film according to any one of claims 1 to 4 as at least a part of the oxide semiconductor thin film; A process including a reduction treatment of the oxide semiconductor of the oxide semiconductor thin film. A method for manufacturing a semiconductor device.

8. It is composed of an oxide sintered body mainly composed of an oxide containing indium, gallium, and aluminum in the following composition, The composition ratios of X, Y, and Z of the oxide semiconductor are the composition ratios of a region surrounded by a line segment connecting points A and B, a line segment connecting points B and C, a line segment connecting points C and D, and a line segment connecting points D and A in a ternary phase diagram of In, Ga, and Al. Sputtering target. Composition: In Ｘ G Ｙ A Ｚ Point A: In １０ Ga ９０ Al ０ Point B: In ３０ Ga ３０ Al ４０ Point C: In ４５ Ga １５ Al ４０ Point D: In ４５ Ga ５５ Al ０

9. In the sputtering target, Relative density is 90% or more The sputtering target of claim 8.

10. A sputtering target having the oxide sintered body according to claim 8 or 9 is manufactured by mixing indium oxide powder, gallium oxide powder, and aluminum oxide powder to form a molded body, and firing the molded body at 1100°C or higher and 1650°C or lower. A method for producing a sputtering target.

11. A sputtering target having the oxide sintered body according to claim 8 or 9 is manufactured by mixing oxides, hydroxides or carbonates of indium, gallium and aluminum and calcining the precursor powder at 1000°C to 1500°C to form a molded body, and calcining the molded body at 1100°C to 1650°C. A method for producing a sputtering target.

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