Ceramic target for indium hydride film formation, method for manufacturing the same, and method for manufacturing a thin-film transistor using the ceramic target.

Abstract

By using an In(OH)3 target, a thin-film transistor with an indium hydride thin film as the active layer is provided in a safe manner without using hydrogen gas. [Solution] A method for manufacturing a thin-film transistor includes the steps of: preparing a substrate equipped with a gate insulating film; forming an active layer on the gate insulating film, forming an active layer made of an indium hydride oxide film; annealing the active layer; forming a source electrode and a drain electrode on the gate insulating film so as to sandwich the active layer; and forming a protective film on the active layer. The active layer formation step is a step of forming an active layer made of an indium hydride oxide film on the gate insulating film by sputtering or pulsed laser deposition using an In(OH)3 target containing indium hydroxide powder and indium oxide powder.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing thin-film transistors for driving pixels in liquid crystal displays and organic EL displays, and more particularly to a method for manufacturing thin-film transistors in which an active layer is formed using a ceramic target for forming an indium hydride film. [Background technology]

[0002] Thin-film transistors with a transparent oxide semiconductor as the active layer are used as pixel driving elements in displays such as large LCD TVs and OLED TVs. For example, in a thin-film transistor using amorphous InGaZnO4 as the transparent oxide semiconductor, the field-effect mobility is 10 cm. 2 / Vs has been obtained (see Patent Document 1).

[0003] Such displays require even higher resolution and faster motion, and next-generation oxide semiconductor thin-film transistors are expected to be 50cm². 2 A field-effect mobility exceeding / Vs is required. Various thin-film transistors using transparent oxide semiconductors as the active layer have been proposed to date. For example, in a thin-film transistor using an indium hydride thin film as the active layer, the field-effect mobility is 140 cm². 2 It has been reported that it is / Vs (see Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 4620046 [Non-patent literature]

[0005] [Non-Patent Document 1] Yusaku Magari, Taiki Kataoka, Wenchang Yeh & Mamoru Furuta, "High-mobility hydrogenated polycrystalline In2O3 (In2O3:H) thin-film transistors", Nature Communications 13, 1078 (2022) [Non-Patent Document 2] Prashant R. Ghediya, Yusaku Magari, Hikaru Sadahira, Takashi Endo, Mamoru Furuta, Yuqiao Zhang, Yasutaka Matsuo, Hiromichi Ohta, "Reliable operation in high-mobility indium oxide thin film transistors", Small Methods 2400578 (2024) [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, while it was confirmed that thin-film transistors using indium hydride thin films as the active layer could achieve the switching speed required for next-generation displays, the sputtering process used to fabricate the indium hydride thin film for the active layer uses hydrogen gas, which is prone to combustion and explosion, thus necessitating a safer manufacturing method.

[0007] In response to this, the inventors succeeded in forming an indium hydride thin film and fabricating a thin-film transistor using it as the active layer without using hydrogen gas, by using a ceramic target made from indium hydroxide (In(OH)3) as a raw material (hereinafter simply referred to as "In(OH)3 target"), thus completing the present invention.

[0008] That is, an object of the present invention is to provide a thin film transistor having an indium hydroxide film as an active layer by using an In(OH)3 target in a safe method without using hydrogen gas.

Means for Solving the Problems

[0009] One aspect of the present invention is a ceramic target for forming an indium hydroxide film (In(OH)3 target), which is a ceramic target containing indium hydroxide powder and indium oxide powder.

[0010] Another aspect of the present invention is a method for manufacturing a ceramic target for forming an indium hydroxide film, including a step of preparing indium hydroxide powder, a step of molding the indium hydroxide powder, a step of firing the molded indium hydroxide compact at a predetermined firing temperature, and is a method for manufacturing a ceramic target including these steps.

[0011] Still another aspect of the present invention is a step of preparing a substrate provided with a gate insulating film, an active layer forming step of forming an active layer made of an indium hydroxide film on the gate insulating film, an annealing step of annealing the active layer, a step of forming source and drain electrodes on the gate insulating film so as to sandwich the active layer, and a step of forming a protective film on the active layer, and the active layer forming step is a method for manufacturing a thin film transistor, which is a step of forming an active layer made of an indium hydroxide film on the gate insulating film by a sputtering method or a pulsed laser deposition method using the ceramic target of the above aspect.

Advantages of the Invention

[0012] In this invention, a thin-film transistor fabricated using an In(OH)3 target can be obtained with a field-effect mobility sufficient for use as a next-generation oxide semiconductor thin-film transistor.

[0013] Furthermore, the active layer can be prepared safely and inexpensively without using flammable and explosive hydrogen gas. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing an overview of the In(OH)3 target fabrication and In2O3 TFT fabrication according to an embodiment of the present invention. [Figure 2] This is a photograph of an In(OH)3 target according to an embodiment of the present invention, with the upper row showing the firing temperature and the lower row showing the density. [Figure 3] These are the results of powder X-ray diffraction (XRD) measurements of an In(OH)3 target according to an embodiment of the present invention. [Figure 4] This is the SIMS analysis result of the hydrogen concentration of an indium hydride oxide (In2O3:H) thin film prepared by the method according to an embodiment of the present invention. [Figure 5] This shows the electron beam backscatter diffraction (EBSD) results for an indium hydride oxide (In2O3:H) thin film fabricated by the method according to an embodiment of the present invention. [Figure 6] Figure 5 shows EBSD images of each thin film. [Figure 7] These are the X-ray diffraction (XRD) measurement results of an indium hydride oxide (In2O3:H) thin film fabricated using an In(OH)3 target according to an embodiment of the present invention. [Figure 8] This is a plan view of a thin-film transistor according to an embodiment of the present invention. [Figure 9] Figure 8 is a cross-sectional view taken in the IX-IX direction. [Figure 10] This is the transistor characteristic of a thin-film transistor according to an embodiment of the present invention. [Modes for carrying out the invention]

[0015] Figure 1 is a schematic diagram showing an overview of the manufacturing process from the fabrication of a ceramic target (In(OH)3 target) for indium hydride film formation according to an embodiment of the present invention to the fabrication of an In2O3 TFT. In the embodiment of the present invention, as shown in Figure 1, (1) an In(OH)3 target is fabricated, (2) an indium hydride film is fabricated using this target as the active layer of a thin-film transistor, (3) solid-phase crystallization annealing is performed, and then (4) a thin-film transistor is fabricated and its characteristics are evaluated. Steps (1) to (4) are described in detail below.

[0016] (1) Fabrication of In(OH)3 target As shown in Figure 1, "(1) In(OH)3 Target Preparation," commercially available In(OH)3 powder was prepared, molded into a molded body using the cold isostatic pressing (CIP) method, and then fired in an electric furnace. The firing temperature was set to near the thermal decomposition temperature of In(OH)3 (150°C, 180°C, 200°C, 250°C), and firing was carried out in air for 24 hours. The In(OH)3 target was prepared using the above process.

[0017] Figure 2 shows a photograph of an In(OH)3 target after firing, with the upper row showing the firing temperature and the lower row showing the target density. The target is disc-shaped with a diameter of approximately 15-25 mm and a thickness of approximately 4-8 mm, and the target density increases to 2.01 g / cm³ as the firing temperature increases. 3 From 1.71 g / cm³ 3 It decreased to 1.7-4.4 g / cm³. The density after firing was 1.7-4.4 g / cm³. 3 A certain degree is desirable.

[0018] Figure 3 shows the results of powder X-ray diffraction (XRD) measurements of the fabricated In(OH)3 target. The horizontal axis represents the diffraction angle 2θ, and the vertical axis represents the intensity. * indicates a peak originating from In(OH)3, ▲ indicates a peak originating from InOOH, and ■ indicates a peak originating from In2O3. In the unsintered sample (w / o) and the samples sintered at 150°C and 180°C, strong diffraction patterns originating from In(OH)3 (2θ=22.4°, 45.6°, 52.9°) and diffraction patterns originating from InOOH (2θ=19.0°, 25.2°, 33.8°) were observed. In samples fired at 200°C, the diffraction patterns originating from In(OH)3 and InOOH were significantly reduced, and instead, diffraction patterns originating from In2O3 (2θ = 21.2, 30.3°, 35.2°, 37.4°, 41.6°, 45.4°, 50.8°, 55.8°, 60.5°) appeared. Furthermore, in samples fired at 250°C, the diffraction pattern originating from In(OH)3 completely disappeared. Thus, it can be seen that by firing at a temperature of 200°C or lower, a ceramic target for creating indium hydride oxide (In2O3:H) films can be obtained. Thus, the ceramic target for creating indium hydride oxide (In2O3:H) films contains indium hydroxide powder and indium oxide powder, and consists of, for example, indium hydroxide powder, indium oxide powder, and unavoidable impurities. In terms of volume fraction, for example, the indium hydroxide powder is between 0.5 percent and 100 percent.

[0019] In this example, cold hydrostatic pressing (CIP) was used to mold the In(OH)3 powder, but other molding methods such as hot hydrostatic pressing (HIP) or hot pressing may also be used.

[0020] (2) Deposition of In2O3:H thin film As shown in “(2) In2O3:H thin film formation” of FIG. 1, using the In(OH)3 target (firing temperatures: 150 °C, 180 °C, 200 °C, 250 °C) fabricated in (1), an amorphous hydrogenated indium oxide (In2O3:H) thin film was formed on a non-alkali glass substrate by pulsed laser deposition (PLD). By using the In(OH)3 target, it is not necessary to introduce hydrogen gas, hydrogen radicals, etc. to introduce hydrogen into the indium oxide film.

[0021] FIG. 4 shows the SIMS analysis results of the hydrogen concentration of the fabricated hydrogenated indium oxide (In2O3:H) thin film, where the horizontal axis represents the depth from the surface of the thin film and the vertical axis represents the hydrogen concentration. For the sample (In2O3) using the conventional indium oxide target and the samples (firing temperatures: 150 °C, 200 °C) using the In(OH)3 target according to the embodiment of the present invention, the hydrogen concentration up to a depth of 50 nm was examined.

[0022] As can be seen from FIG. 4, in the sample (In2O3) using the conventional indium oxide target, the hydrogen concentration is about 3 to 4×10 20 cm -3 whereas in the samples using the In(OH)3 target according to the embodiment of the present invention, the hydrogen concentrations are about 1×10 22 cm -3 (firing temperature: 150 °C) and about 5×10 21 cm -3 (firing temperature: 200 °C).

[0023] [[ID=二十三]] Thus, by using the In(OH)3 target according to the embodiment of the present invention, it can be seen that, without introducing hydrogen gas, it has a hydrogen concentration more than 10 times that of the hydrogenated indium oxide thin film fabricated using the conventional indium oxide target.

[0024] (3) Solid-phase crystallization As shown in "(3) Solid-phase crystallization (~300°C)" in Figure 1, amorphous indium hydride oxide (In2O3:H) thin films (fired at 150°C, 180°C, 200°C, and 250°C) prepared in (2) were crystallized by annealing in air at 300°C for 30 minutes to form polycrystalline indium oxide films. For comparison, indium oxide thin films (In2O3) prepared using a conventional indium oxide target were also subjected to the same annealing process.

[0025] Figure 5 shows the crystallinity of the indium oxide film after annealing, evaluated using electron beam backscatter diffraction (EBSD). The horizontal axis represents grain size (lateral grain size), and the vertical axis represents area fraction.

[0026] Compared to indium oxide thin films (In2O3) fabricated using conventional indium oxide targets, the indium hydride oxide (In2O3:H) thin films fabricated using the In(OH)3 target according to the embodiment of the present invention exhibit larger particle size and area ratios. In particular, when using an In(OH)3 target fired at a firing temperature of 200°C, both particle size and area ratio are maximized.

[0027] Figure 6 shows EBSD images of each of the thin films in Figure 5. (a) is an indium oxide thin film fabricated using a conventional indium oxide target, and (b) to (e) are indium hydride oxide (In2O3:H) thin films fabricated using an In(OH)3 target according to an embodiment of the present invention. The firing temperatures were (b) 150°C, (c) 180°C, (d) 200°C, and (e) 250°C.

[0028] The indium hydride thin film (as-depo film) (not shown) immediately after deposition (before annealing) was an amorphous thin film. This is thought to be because hydrogen is supplied from the In(OH)3 target during the deposition process, inhibiting the crystallization of the film.

[0029] Next, by annealing the indium hydride thin film (as-depo film) in air at 300°C for 30 minutes, the hydrogen concentration in the indium hydride thin film changed, and consequently, crystal growth occurred, changing the structure from amorphous to polycrystalline.

[0030] In particular, the particle size of the indium oxide (In2O3:H) thin film prepared using an In(OH)3 target fired at 200°C (d) increased significantly (>2 μm). This is because the hydrogen concentration in the indium oxide (In2O3:H) prepared using those In(OH)3 targets differs depending on the firing temperature of the In(OH)3 target.

[0031] Furthermore, (a) in indium oxide thin films (In2O3) fabricated using conventional indium oxide targets, aggregates of fine particles (~200 nm) were observed in the film immediately after deposition (as-depo), and crystallization hardly occurred even after similar annealing.

[0032] Figure 7 shows the X-ray diffraction (XRD) measurement results of indium hydride oxide (In2O3:H) thin films fabricated using an In(OH)3 target. (a) shows the measurement results for the thin film in the as-depo state, and (b) shows the measurement results for the thin film after annealing (300°C, 30 minutes). The horizontal axis represents the diffraction angle 2θ, and the vertical axis represents the intensity.

[0033] Similar to Figures 5 and 6, measurements were performed on indium oxide thin films (In2O3) prepared using a conventional indium oxide target, and indium hydride oxide (In2O3:H) thin films (firing temperatures: 150°C, 180°C, 200°C, 250°C) prepared using an In(OH)3 target according to an embodiment of the present invention.

[0034] As can be seen from Figure 7(a), in the as-depo state, the indium oxide thin film (In2O3) fabricated using an indium oxide target shows a diffraction pattern indicating polycrystalline structure, but the indium hydride oxide (In2O3:H) thin film fabricated using an In(OH)3 target does not show this diffraction pattern, indicating that it is in an amorphous state.

[0035] On the other hand, after annealing, a diffraction pattern indicating polycrystalline properties can be observed even in the indium hydride oxide (In2O3:H) thin film fabricated using an In(OH)3 target. Thus, this measurement result also shows that polycrystalline properties occur in the indium hydride oxide (In2O3:H) thin film fabricated using an In(OH)3 target according to the embodiment of the present invention when annealed.

[0036] (4) Fabrication of In2O3 TFTs As shown in "(4) In2O3 TFT Fabrication" in Figure 1, thin-film transistors were actually fabricated using indium oxide (In2O3:H) thin films (firing temperatures: 150°C, 180°C, 200°C, 250°C) prepared using an In(OH)3 target according to an embodiment of the present invention, and the transistor characteristics were evaluated.

[0037] Figure 8 is a top view of a thin-film transistor according to an embodiment of the present invention, where the entire structure is represented by 100, and Figure 9 is a cross-sectional view of Figure 8 as seen in the IX-IX direction.

[0038] As shown in Figures 8 and 9, first, an alkali-free glass substrate 10 with a commercially available ITO (Indium Tin Oxide) film (gate electrode) 20 attached was prepared.

[0039] Next, a gate insulating film 30 made of aluminum oxide with a thickness of 100 nm was deposited on top of it by atomic layer deposition.

[0040] Next, an amorphous In2O3:H thin film (5 nm) was deposited via a metal mask using pulsed laser deposition (PLD) with an In(OH)3 target to form the active layer 40. The hydrogen concentration in the active layer 40 has an upper limit of 2 / 3 / 3 in terms of the atomic ratio of In / O / H, and a lower limit of 0.1 atm% relative to the indium concentration. Since this process does not use flammable and explosive hydrogen gas, it can be a safe manufacturing process, and inexpensive manufacturing equipment can be used.

[0041] Next, the material was annealed in air at 300°C for 30 minutes to induce amorphous crystallization, forming a polycrystalline In2O3:H thin film active layer 40.

[0042] Next, an ITO thin film (100 nm) was deposited as the source electrode 50 and drain electrode 60 via another metal mask.

[0043] Next, a yttrium oxide film (50 nm) was deposited on the surface of the polycrystalline In2O3:H thin film as a protective film 70. Finally, a post-annealing treatment was performed in air at 350°C for 30 minutes.

[0044] As a comparative example, a thin-film transistor 200 was fabricated by depositing an amorphous In2O3:H thin film (5 nm) via a metal mask using a conventional pulsed laser deposition method with an In2O3 target. The configuration other than the amorphous In2O3:H thin film (5 nm) is the same as that of the thin-film transistor 100 according to the embodiment of the present invention.

[0045] The transistor characteristics of thin-film transistors 100 and 200 were measured at room temperature in air using a semiconductor device analyzer (B1500A). The channel length of thin-film transistors 100 and 200 is 200 μm, and the channel width is 400 μm. The capacitance of the gate insulator is 70 nF / cm². 2 That is the case.

[0046] Figure 10 shows the measured transistor characteristics, with the horizontal axis representing the gate voltage, and the vertical axis showing the drain voltage on the left and the field-effect mobility on the right. The transistor characteristics were measured with a drain voltage of 5V (constant) and drain current (I D ) and field effect mobility (μ FE ) gate voltage (V g The dependence (transfer characteristics) was measured. In Figure 10, (a) shows the measurement results of a thin-film transistor 200 fabricated using an In2O3 target as a comparative example, and (b) to (e) show the measurement results of a thin-film transistor 100 fabricated using an In(OH)3 target according to an embodiment of the present invention (firing temperature: 150°C, 180°C, 200°C, 250°C).

[0047] As shown in (a), in the comparative example thin-film transistor 200, the gate voltage (V g Even if ) is set to -10V, the drain current (I D ) is 10 -5 ~10 -6 The gate voltage was around A, and it did not completely turn off, so switching characteristics could not be obtained. On the other hand, as shown in (b) to (e), in the thin-film transistor 100 according to the embodiment of the present invention, the gate voltage (V g ) is -10V and drain current (I D ) is 10 -12 The result was approximately level A, indicating good switching characteristics.

[0048] Furthermore, in the thin-film transistors 100 of (b) to (e), the field-effect mobility is 70 to 90 cm. 2 / Vs) becomes 50cm 2 Good values ​​exceeding / Vs were obtained. In particular, for thin-film transistor 100 fired at a firing temperature of 200°C, the value was approximately 90 (cm²). 2 The result was ( / Vs), and a sufficiently high field-effect mobility was obtained.

[0049] As shown in Table 1, to obtain good transistor threshold voltage and field-effect mobility, the hydroxyl group concentration (=hydrogen concentration) on the surface of the active layer, which is made of an indium hydride film, should be, for example, 1 × 10⁻⁶ 13 ~1 × 10 16 pieces / cm 2Preferably 1 × 10 14 ~1 × 10 15 pieces / cm 2 That is the case.

[0050] Table 1 TIFF2026046240000002.tif83145

[0051] The thin-film transistor 100 fabricated here is just one example; the protective film 70 may also be made of other rare-earth oxides such as erbium oxide, gadolium oxide, or ytterbium oxide (Ln2O3, where Ln is a rare-earth element). Furthermore, the gate electrode 20, gate insulating film 30, source electrode 50, and drain electrode 60 may be made of other common materials. Moreover, the thickness of each layer is not limited to these examples.

[0052] As described above, the thin-film transistor fabricated using the In(OH)3 target according to the embodiment of the present invention achieves a field-effect mobility sufficient for use as a next-generation oxide semiconductor thin-film transistor. Furthermore, since flammable and explosive hydrogen gas is not used in the fabrication of the active layer, the manufacturing method can be made safer and less expensive. [Industrial applicability]

[0053] The present invention can be used for pixel driving devices for displays, particularly for next-generation displays that require high resolution and high speed. [Explanation of symbols]

[0054] 10 Glass substrate 20 gates 30 Gate insulating film 40 Active layer (In2O3:H thin film) 50 source electrodes 60 Drain electrodes 70 Protective film 100, 200 thin-film transistors

Claims

1. A ceramic target for forming indium hydride oxide films, A ceramic target containing indium hydroxide powder and indium oxide powder.

2. The ceramic target according to claim 1, comprising indium hydroxide powder, indium oxide powder, and unavoidable impurities.

3. The ceramic target according to claim 1, wherein the volume fraction of the indium hydroxide powder and the indium oxide powder is 0.5 percent or more and 100 percent or less for the indium hydroxide powder.

4. The density of the ceramic target is 1.7 to 4.4 g / cm³. ３ The target according to claim 1.

5. The ceramic target according to claim 1, wherein the method for forming the indium hydride film is sputtering or pulsed laser deposition.

6. A method for manufacturing a ceramic target for forming an indium hydride oxide film, The process of preparing indium hydroxide powder, The process of molding the indium hydroxide powder, A step of firing the molded indium hydroxide molded body at a predetermined firing temperature, A method for manufacturing a ceramic target containing [a specific component].

7. The manufacturing method according to claim 6, wherein the firing temperature is 150°C to 250°C.

8. A step of preparing a substrate equipped with a gate insulating film, The process involves forming an active layer consisting of an indium hydride film on the gate insulating film, An annealing step for annealing the active layer, A step of forming a source electrode and a drain electrode on the gate insulating film such that the active layer is sandwiched between them, The step includes forming a protective film on the active layer, A method for manufacturing a thin-film transistor, wherein the active layer formation step is a step of forming an active layer made of an indium hydride film on the gate insulating film by a sputtering method or pulsed laser deposition method using a target according to any one of claims 1 to 5.

9. The manufacturing method according to claim 8, wherein the activated layer formation step is carried out without introducing hydrogen gas.

10. The manufacturing method according to claim 8, wherein the annealing step is performed at 150 to 450°C.

11. The hydroxyl group concentration on the surface of the active layer after the annealing process is 1 × 10⁻⁶ １３ ~1 x 10 １５ pieces / cm ２ The manufacturing method according to claim 8.

12. The manufacturing method according to claim 8, wherein the crystal grain size of the active layer after the annealing step is 50 nm or more.

13. The manufacturing method according to claim 8, wherein a post-annealing step is performed after the formation of the protective film.

14. The manufacturing method according to claim 8, wherein the active layer is an indium hydride film in which the upper limit of the hydrogen concentration is 2 / 3 / 3 in terms of the atomic ratio of In / O / H, and the lower limit of the hydrogen concentration is 0.1 atm% relative to the indium concentration.

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