Semiconductor device and method for manufacturing the same

Abstract

To provide a semiconductor device that suppresses a reduction of a pixel aperture ratio.SOLUTION: A semiconductor device includes a first gate electrode, an oxide semiconductor layer having a first oxide semiconductor with a polycrystalline structure on the first gate electrode, a source electrode and a drain electrode electrically connected to the oxide semiconductor layer, and a second gate electrode superimposed on the first gate electrode and oxide semiconductor layer on the source and drain electrodes, and the second gate electrode includes a second oxide semiconductor having a polycrystalline structure, and the second gate electrode is electrically connected to the first gate electrode.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] An embodiment of the present invention relates to a semiconductor device using an oxide semiconductor having a polycrystalline structure. [Background technology]

[0002] In recent years, semiconductor devices using oxide semiconductor films as channels instead of silicon semiconductor films using amorphous silicon, low-temperature polysilicon, single crystal silicon, etc. have been developed (see, for example, Patent Documents 1 to 6). A semiconductor device including such an oxide semiconductor film can be formed with a simple structure and a low-temperature process, similar to a semiconductor device including an amorphous silicon film. In addition, a semiconductor device including an oxide semiconductor film is known to have a higher field-effect mobility than a semiconductor device including an amorphous silicon film. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-141338 A [Patent Document 2] JP 2014-099601 A [Patent Document 3] Patent Publication No. 2021-153196 [Patent Document 4] JP 2018-006730 A [Patent Document 5] JP 2016-184771 A [Patent Document 6] Patent Publication No. 2021-108405 Summary of the Invention [Problem to be solved by the invention]

[0004] The semiconductor device is formed, for example, in a pixel of a display device. As display devices become more highly fine, it is necessary for the semiconductor device to not only have high field effect mobility but also to suppress a decrease in the aperture ratio of the pixel. One object of one embodiment of the present invention is to provide a semiconductor device that suppresses a decrease in the aperture ratio of the pixel. Another object of one embodiment of the present invention is to provide a method for manufacturing a semiconductor device that suppresses a decrease in the aperture ratio of the pixel. [Means for solving the problem]

[0005] A semiconductor device according to one embodiment of the present invention includes a first gate electrode, an oxide semiconductor layer on the first gate electrode, the oxide semiconductor layer including a first oxide semiconductor having a polycrystalline structure, a source electrode and a drain electrode electrically connected to the oxide semiconductor layer, and a second gate electrode on the source electrode and the drain electrode overlapping with the first gate electrode and the oxide semiconductor layer, the second gate electrode including a second oxide semiconductor having a polycrystalline structure, and the second gate electrode electrically connected to the first gate electrode.

[0006] A method for manufacturing a semiconductor device according to one embodiment of the present invention includes forming a first gate electrode, forming an oxide semiconductor layer containing a first oxide semiconductor having a polycrystalline structure on the first gate electrode, forming a source electrode and a drain electrode in contact with the oxide semiconductor layer, forming a first oxide semiconductor film on the source electrode and the drain electrode, performing a heat treatment on the first oxide semiconductor film, forming a second gate electrode containing a second oxide semiconductor having a polycrystalline structure, and forming a nitride layer covering the second gate electrode. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic exploded perspective view showing a configuration of a display device. [Diagram 2] FIG. 2 is a schematic plan view showing a circuit configuration of the display device. [Diagram 3] 1 is a schematic plan view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Figure 4]1 is a schematic cross-sectional view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Diagram 5] 1 is a flowchart illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 6] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 7] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 8] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 9] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 10] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 11] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 12] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 13] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 14] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 15] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 16] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 17] 1 is a flowchart illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 18] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 19] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 20] 1 is a flowchart illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 21] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 22] 1 is a schematic plan view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Figure 23] 1 is a schematic cross-sectional view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Figure 24] 1 is a schematic plan view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Diagram 25] 1 is a schematic cross-sectional view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Figure 26] 1 is a flowchart illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 27] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 28] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 29] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Diagram 30] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Diagram 31] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Diagram 32] 1 is a schematic plan view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Diagram 33] 1 is a schematic cross-sectional view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Diagram 34] 1 is a flowchart illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Diagram 35] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Diagram 36] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 37] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 38] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 39] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following disclosure is merely an example. A configuration that a person skilled in the art can easily come up with by appropriately modifying the configuration of the embodiment while maintaining the gist of the invention is naturally included in the scope of the present invention. In order to make the explanation clearer, the drawings may be schematic in terms of the width, film thickness, shape, etc. of the components compared to the actual embodiment. However, the illustrated shapes are merely examples and do not limit the interpretation of the present invention. In this specification and each figure, components similar to those described above with respect to the previous figures may be given the same reference numerals, and detailed explanations may be omitted as appropriate.

[0009] In this specification, the direction from the substrate toward the oxide semiconductor layer is referred to as "upper" or "upper". Conversely, the direction from the oxide semiconductor layer toward the substrate is referred to as "lower" or "lower". Thus, for convenience of explanation, the terms "upper" and "lower" are used in the explanation, but the vertical relationship between the substrate and the oxide semiconductor layer may be arranged in the opposite direction to that shown in the figure. In addition, the expression "oxide semiconductor layer on the substrate" merely describes the vertical relationship between the substrate and the oxide semiconductor layer, and other members may be arranged between the substrate and the oxide semiconductor layer. "Upper" and "lower" refer to the order of stacking in a structure in which multiple layers are stacked, and when a pixel electrode is expressed as being above a semiconductor device, the semiconductor device and the pixel electrode may not overlap in a planar view. On the other hand, when a pixel electrode is expressed as being vertically above a semiconductor device, the semiconductor device and the pixel electrode may overlap in a planar view. Note that the planar view refers to a view from a direction perpendicular to the surface of the substrate.

[0010] In this specification and the like, unless otherwise specified, expressions such as "α includes A, B, or C," "α includes any one of A, B, and C," and "α includes one selected from the group consisting of A, B, and C" do not exclude cases where α includes multiple combinations of A to C. Furthermore, these expressions do not exclude cases where α includes other components.

[0011] In this specification and the like, the term "semiconductor device" refers to a device in general that can function by utilizing semiconductor characteristics. Transistors and semiconductor circuits are included in one form of semiconductor device. The semiconductor device of the embodiment described below may be, for example, a display device, an integrated circuit (IC) such as a microprocessor (Micro-Processing Unit: MPU), or a transistor used in a memory circuit.

[0012] In this specification, the term "display device" refers to a structure that displays an image using an electro-optical layer. For example, the term display device may refer to a display panel including an electro-optical layer, or may refer to a structure in which other optical members (e.g., a polarizing member, a backlight, a touch panel, etc.) are attached to a display cell. The term "electro-optical layer" may include a liquid crystal layer, an electroluminescent (EL) layer, an electrochromic (EC) layer, and an electrophoretic layer, unless technically inconsistent.

[0013] In this specification and the like, the terms "film" and "layer" may be interchangeable in some cases.

[0014] The following embodiments can be combined with each other as long as no technical contradiction occurs.

[0015] First Embodiment [1. Configuration of display device 1] A display device 1 including a semiconductor device 10 according to an embodiment of the present invention will be described with reference to FIGS.

[0016] Fig. 1 is a schematic exploded perspective view showing the configuration of the display device 1. Fig. 2 is a schematic plan view showing the circuit configuration of the display device 1.

[0017] As shown in FIG. 1, the display device 1 includes a display unit 2 and a light source unit 3. In the display device 1, the light source unit 3 emits light to the display unit 2. The light source unit 3 includes, for example, a light emitting diode (LED). The light source unit 3 may include a plurality of LEDs. When the light source unit 3 includes a plurality of LEDs, LEDs of the same color may be used, or LEDs of different colors may be used. Note that the light source unit 3 is not limited to a configuration including an LED. The light source unit 3 may include an element or device capable of emitting light. The light source unit 3 may also include a light guide plate or an optical sheet. In the display device 1 shown in FIG. 1, the light source unit 3 is disposed below the display unit 2, but the light source unit 3 may be disposed to the side of the display unit 2.

[0018] The display unit 2 includes a first substrate 100 and a second substrate 300. A liquid crystal layer (not shown) is sandwiched between the first substrate 100 and the second substrate 300. As shown in FIG. 2, a display section DP, a scanning line driving circuit GD (the scanning line driving circuit may be called a gate driver), a signal line driving circuit SD (the signal line driving circuit may be called a source driver), and a terminal section TP are provided on the first substrate 100. The display section DP is provided in the center of the first substrate 100. The scanning line driving circuit GD is provided outside the display section DP along the y direction. The signal line driving circuit SD is provided outside the display section DP along the x direction. The terminal section TP is provided at an end of the first substrate 100.

[0019] The scanning line driving circuit GD and the signal line driving circuit SD are electrically connected to the terminal portion TP. A flexible printed circuit board FPC is connected to the terminal portion TP, and signals from the driving elements DRV are input to the terminal portion TP (see FIG. 1). That is, the signals from the driving elements DRV are input to the scanning line driving circuit GD and the signal line driving circuit SD via the terminal portion TP.

[0020] The display unit DP includes a plurality of pixels PX, a plurality of scanning lines GL (the scanning lines may be referred to as gate lines), and a signal line SL (the signal line may be referred to as a source line). Each of the plurality of pixels PX is provided in an area surrounded by the scanning line GL and the signal line SL. The scanning line GL is electrically connected to a scanning line driving circuit GD and extends along the x direction. A first signal generated by the scanning line driving circuit GD is input to the scanning line GL. The signal line SL is electrically connected to a signal line driving circuit SD and extends along the y direction. A second signal generated by the signal line driving circuit SD is input to the signal line SL. Each of the plurality of pixels PX is controlled based on the first signal and the second signal.

[0021] Each of the pixels PX includes a semiconductor device 10 and a liquid crystal element 20. The semiconductor device 10 shown in FIG. 2 is a so-called transistor, but the configuration of the semiconductor device 10 is not limited to a transistor itself as long as it includes a transistor. In each of the pixels PX, the semiconductor device 10 is controlled based on a first signal and a second signal to drive the liquid crystal element. In this embodiment, the semiconductor device 10 included in the pixel PX of the display device 1 is described, but the semiconductor device 10 can also be used in the scanning line driving circuit GD and the signal line driving circuit SD. In addition, the display device 1 is a so-called liquid crystal display device, but may be another display device.

[0022] 2. Configuration of Semiconductor Device 10 A semiconductor device 10 according to an embodiment of the present invention will be described with reference to FIGS.

[0023] Fig. 3 is a schematic plan view showing the configuration of a semiconductor device 10 according to one embodiment of the present invention. Fig. 4 is a schematic cross-sectional view showing the configuration of a semiconductor device 10 according to one embodiment of the present invention. Fig. 4 is a cross-sectional view of the semiconductor device 10 taken along line A1-A2 in Fig. 3.

[0024] As shown in FIG. 4, the semiconductor device 10 includes a first substrate 100, a first gate electrode 110, a scanning line 120, a first insulating layer 130, an oxide semiconductor layer 140, a source electrode 150, a drain electrode 160, a connection electrode 170, a second insulating layer 180, a second gate electrode 190, and a nitride layer 200. The first gate electrode 110 and the scanning line 120 are provided on the first substrate 100. The first insulating layer 130 covers the upper surfaces and end surfaces of the first gate electrode 110 and the scanning line 120, and is provided on the first gate electrode 110 and the scanning line 120. The first insulating layer 130 has a first opening OP1 through which a part of the upper surface of the scanning line 120 is exposed. The oxide semiconductor layer 140 is provided on the first insulating layer 130, overlapping the first gate electrode 110. Each of the source electrode 150 and the drain electrode 160 covers a part of the upper surface and a part of the end surface of the oxide semiconductor layer 140, and is provided on the first insulating layer 130. The connection electrode 170 is provided on the first insulating layer 130 and contacts the scanning line 120 through a first opening OP1. The second insulating layer 180 covers the upper surface of the oxide semiconductor layer 140, the upper surface and end surface of the source electrode 150, the upper surface and end surface of the drain electrode 160, and the upper surface and end surface of the connection electrode 170, and is provided on the first insulating layer 130. The second insulating layer 180 has a second opening OP2 through which a part of the connection electrode 170 is exposed. The second gate electrode 190 is provided on the second insulating layer 180, overlapping the oxide semiconductor layer 140 and the connection electrode 170. The second gate electrode 190 contacts the connection electrode 170 through the second opening OP2. The nitride layer 200 covers the top and end surfaces of the second gate electrode 190 and is disposed on the second insulating layer 180 .

[0025] 3, the first gate electrode 110 is provided so as to protrude in the y direction from the scanning line extending in the x direction, and is formed continuously with the scanning line 120. In other words, the first gate electrode is formed in the same layer as the scanning line 120. In addition, the source electrode 150, the drain electrode 160, and the connection electrode 170 are provided spaced apart from each other, but the source electrode 150, the drain electrode 160, and the connection electrode 170 are formed in the same layer.

[0026] The first gate electrode 110 is formed continuously with the scanning line 120, and it can be said that the first gate electrode 110 is electrically connected to the scanning line. The second gate electrode 190 is electrically connected to the first gate electrode 110 via the connection electrode 170. Therefore, the voltage included in the signal input to the scanning line 120 is applied to both the first gate electrode 110 and the second gate electrode 190.

[0027] The source electrode 150 is electrically connected to a signal line (the signal line here corresponds to the signal line SL in FIG. 2 and is not shown in FIGS. 3 and 4). The drain electrode 160 is electrically connected to a pixel electrode (not shown) provided in the pixel PX. A liquid crystal layer provided between the first substrate 100 and the second substrate 300 is driven by an electric field generated between the pixel electrode provided on the first substrate 100 and a counter electrode (not shown) provided on the second substrate 300. By driving the liquid crystal layer in each of the multiple pixels PX, the transmission of light emitted from the light source unit 3 in each of the multiple pixels PX is controlled. In the pixel PX, some of the components of the semiconductor device 10 block the light emitted from the light source unit 3.

[0028] Depending on the configuration of the semiconductor device, the aperture ratio of the pixel PX may decrease. In particular, when the size of the pixel PX becomes smaller, the proportion of the semiconductor device increases, and the decrease in the aperture ratio of the pixel PX becomes noticeable. However, in the semiconductor device 10, since the second gate electrode 190 has light-transmitting properties, the decrease in the aperture ratio of the pixel PX can be suppressed.

[0029] In plan view, the second gate electrode 190 includes a region overlapping any one of the first gate electrode 110, the scanning line 120, the source electrode 150, and the drain electrode 160 (hereinafter referred to as an "overlapping region"), while also including a region not overlapping the first gate electrode 110, the scanning line 120, the source electrode 150, and the drain electrode 160 (hereinafter referred to as a "non-overlapping region"). Since the non-overlapping region is a region through which light emitted from the light source unit 3 passes, if the non-overlapping region has a light-shielding property, the aperture ratio of the pixel PX decreases. However, in the semiconductor device 10, since the non-overlapping region of the second gate electrode 190 has a light-transmitting property, it is possible to suppress a decrease in the aperture ratio of the pixel PX while ensuring the degree of freedom in arranging the second gate electrode 190.

[0030] Here, a more detailed description will be given of each of the above-mentioned components of the semiconductor device 10. The detailed configurations of the oxide semiconductor layer 140 and the second gate electrode 190 will be described later.

[0031] The first substrate 100 can support each layer constituting the semiconductor device 10. For example, the first substrate 100 can be a rigid substrate having light-transmitting properties, such as a glass substrate, a quartz substrate, or a sapphire substrate. The first substrate 100 can also be a rigid substrate having no light-transmitting properties, such as a silicon substrate. The first substrate 100 can also be a flexible substrate having light-transmitting properties, such as a polyimide resin substrate, an acrylic resin substrate, a siloxane resin substrate, or a fluorine resin substrate. In order to improve the heat resistance of the first substrate 100, impurities may be introduced into the flexible substrate. The second substrate 300 can be a substrate similar to the first substrate 100.

[0032] Each of the first insulating layer 130 and the second insulating layer 180 can function as a gate insulating layer. For example, silicon oxide (SiO x ), silicon oxynitride (SiO x N y ), aluminum oxide (AlO x), or aluminum oxide nitride (AlO x N y ), or silicon nitride (SiN x ), silicon oxynitride (SiN x O y ), Aluminum Nitride (AlN x ), or aluminum oxide nitride (AlN x O y Each of the first insulating layer 130 and the second insulating layer 180 may have a single-layer structure or a multilayer structure.

[0033] Here, silicon oxynitride (SiO x N y ) and aluminum oxide nitride (AlO x N y ) are oxides that contain a smaller ratio (x>y) of nitrogen (N) than oxygen (O). Silicon oxynitride (SiN x O y ) and aluminum oxide nitride (AlN x O y ) is a nitride containing a smaller ratio of oxygen than nitrogen (x>y). For convenience of explanation, silicon oxide (SiO x ) and silicon oxynitride (SiO x N y ) is simply called "silicon oxide" and silicon nitride (SiN x ) and silicon oxynitride (SiN x O y ) is sometimes simply called "silicon nitride". Similarly, aluminum oxide (AlO x ) and aluminum oxide nitride (AlO x N y ) is simply called "aluminum oxide" and aluminum nitride (AlN x ) and aluminum oxide nitride (AlN x O y ) is sometimes simply called "aluminum nitride."

[0034] The oxide semiconductor layer 140 is preferably in contact with an oxide. When the oxide semiconductor layer 140 is in contact with an oxide, oxygen can be supplied from the oxide to the oxide semiconductor layer 140 by heat treatment. Therefore, when the first insulating layer 130 and the second insulating layer 180 each have a single-layer structure, it is preferable that silicon oxide is used for each of the first insulating layer 130 and the second insulating layer 180. In addition, when the first insulating layer 130 has a stacked structure, it is preferable that the first insulating layer 130 has a structure in which silicon oxide is stacked on silicon nitride so that the silicon oxide is in contact with the oxide semiconductor layer 140. Similarly, when the second insulating layer 180 has a stacked structure, it is preferable that the second insulating layer 180 has a structure in which silicon nitride is stacked on silicon oxide so that the silicon oxide is in contact with the oxide semiconductor layer 140.

[0035] The first gate electrode 110 preferably has not only electrical conductivity but also a function of reflecting or absorbing light emitted from the light source unit 3. That is, the first gate electrode 110 preferably has a light-shielding function. In a plan view, the first gate electrode 110 overlaps with the entire oxide semiconductor layer 140 (see FIG. 3). Therefore, when the first gate electrode 110 has a light-shielding function, it is possible to block light incident on the oxide semiconductor layer 140. As described above, the first gate electrode 110 is formed in the same layer as the scanning line 120. That is, the first gate electrode 110 is formed of the same material as the scanning line 120. For example, the first gate electrode 110 and the scanning line 120 can be made of metals such as aluminum (Al), copper (Cu), titanium (Ti), molybdenum (Mo), or tungsten (W), or alloys or compounds thereof. The first gate electrode 110 and the scanning line 120 may have a single-layer structure or a laminated structure.

[0036] The source electrode 150, the drain electrode 160, and the connection electrode 170 are conductive. As described above, the source electrode 150, the drain electrode 160, and the connection electrode 170 are formed in the same layer. That is, the source electrode 150, the drain electrode 160, and the connection electrode 170 are formed of the same material. The source electrode 150, the drain electrode 160, and the connection electrode 170 are formed of the same material as the first gate electrode 110 and the scanning line 120. can be used.

[0037] The nitride layer 200 can function as an interlayer insulating layer. In addition, the nitride layer 200 can also function as a hydrogen supply layer to the second gate electrode 190, which will be described in detail later. For example, the nitride layer 200 can be made of silicon nitride (SiN x ), silicon oxynitride (SiN x O y ), Aluminum Nitride (AlN x ), or aluminum oxide nitride (AlN x O y ) can be used.

[0038] [3. Configuration of Oxide Semiconductor Layer 140] [3-1. Composition of the oxide semiconductor layer 140] An oxide semiconductor containing two or more metal elements including indium (In) is used as the oxide semiconductor layer 140. As the metal elements other than indium, gallium (Ga), zinc (Zn), aluminum (Al), hafnium (Hf), yttrium (Y), zirconium (Zr), and lanthanoids are used.

[0039] The oxide semiconductor layer 140 has a light-transmitting property and a polycrystalline structure including a plurality of crystal grains. In order for the oxide semiconductor layer 140 to have a polycrystalline structure, it is preferable to use an oxide semiconductor in which the ratio of indium to all metal elements is 50% or more in atomic ratio. When the ratio of indium is large, the oxide semiconductor layer 140 is more likely to crystallize. In addition, it is preferable to contain gallium as a metal element other than indium. Gallium belongs to the same Group 13 element as indium. Therefore, the crystallinity of the oxide semiconductor layer 140 is hardly impaired by gallium.

[0040] Although the details will be described later, the oxide semiconductor layer 140 has properties different from those of conventional oxide semiconductors having a polycrystalline structure. Therefore, in order to distinguish the oxide semiconductor contained in the oxide semiconductor layer 140 from conventional oxide semiconductors having a polycrystalline structure, the oxide semiconductor contained in the oxide semiconductor layer 140 will be referred to as Poly-OS (Poly-crystalline Oxide Semiconductor) in the following description.

[0041] The Poly-OS included in the oxide semiconductor layer 140 can be formed by sputtering and heat treatment. Here, a method for forming the oxide semiconductor layer 140 will be described.

[0042] First, an oxide semiconductor film is formed by sputtering. The formed oxide semiconductor film has an amorphous structure. Here, the amorphous structure refers to a structure in which a long-range ordered structure does not exist and a periodic crystal lattice arrangement is not observed. For example, when an oxide semiconductor film having an amorphous structure is observed by X-ray diffraction (XRD), a specific peak based on a crystal structure is not obtained in the diffraction pattern. Note that an oxide semiconductor film having an amorphous structure may have a short-range ordered structure in a micro domain. However, such an oxide semiconductor film does not exhibit the characteristics of Poly-OS, and therefore can be classified as an oxide semiconductor film having an amorphous structure.

[0043] An oxide semiconductor film having an amorphous structure is formed at a low temperature. For example, the temperature of the substrate on which the oxide semiconductor film is formed is 150° C. or lower, preferably 100° C. or lower, and more preferably 50° C. or lower. When the substrate temperature is high, microcrystals are likely to be generated in the oxide semiconductor film to be formed. In addition, the oxygen partial pressure in the chamber during film formation is 1% to 10%, preferably 1% to 5%, and more preferably 2% to 4%. When the oxygen partial pressure is high, microcrystals are generated in the oxide semiconductor film due to excess oxygen contained in the oxide semiconductor. On the other hand, under conditions where the oxygen partial pressure is less than 1%, the oxygen composition in the oxide semiconductor film becomes nonuniform, and an oxide semiconductor film containing many microcrystals or an oxide semiconductor film that does not crystallize even when heat treatment is performed is formed.

[0044] Next, the oxide semiconductor film formed by sputtering is subjected to heat treatment. The heat treatment is performed in air, but the atmosphere is not limited thereto. The heat treatment temperature is 300° C. to 500° C., and preferably 350° C. to 450° C. The heat treatment time is 15 minutes to 120 minutes, and preferably 30 minutes to 60 minutes. By performing the heat treatment, the oxide semiconductor film having an amorphous structure is crystallized, and an oxide semiconductor layer 140 containing Poly-OS is formed.

[0045] The composition of the oxide semiconductor layer 140 is approximately equal to the composition of the sputtering target. Therefore, the composition of the metal elements of the oxide semiconductor layer 140 can be specified based on the composition of the metal elements of the sputtering target. The composition of the oxide semiconductor layer 140 may be specified by using an XRD method. Specifically, the composition of the metal elements of the oxide semiconductor layer 140 can be specified based on the crystal structure and lattice constant of the oxide semiconductor layer 140 obtained by the XRD method. Furthermore, the composition of the metal elements of the oxide semiconductor layer 140 can also be specified by using an X-ray fluorescence analysis or an Electron Probe Micro Analyzer (EPMA) analysis. Note that the oxygen contained in the oxide semiconductor layer 140 is not limited to this because it changes depending on the process conditions of the sputtering.

[0046] [3-2. Characteristics of the oxide semiconductor layer 140] Next, characteristics of the oxide semiconductor layer 140 containing Poly-OS will be described.

[0047] The oxide semiconductor layer 140 has excellent etching resistance. Specifically, the etching rate of the oxide semiconductor layer 140 is very small when the oxide semiconductor layer 140 is etched using an etching solution for wet etching. This means that the oxide semiconductor layer 140 is hardly etched by the etching solution. The etching rate of the oxide semiconductor layer 140 when the oxide semiconductor layer 140 is etched using an etching solution containing phosphoric acid as a main component at 40° C. (hereinafter, referred to as a mixed acid etching solution) is less than 3 nm / min, less than 2 nm / min, or less than 1 nm / min. The ratio of phosphoric acid in the mixed acid etching solution is 50% or more, 60% or more, or 70% or more. The mixed acid etching solution may contain acetic acid and nitric acid in addition to phosphoric acid. Note that, in an oxide semiconductor film not containing Poly-OS, for example, an oxide semiconductor film having an amorphous structure before heat treatment, the etching rate of the oxide semiconductor film when the oxide semiconductor film is etched using a mixed acid etching solution at 40° C. is 100 nm / min or more. Furthermore, the etching rate when the oxide semiconductor layer 140 is etched using a 0.5% hydrofluoric acid solution at room temperature is less than 5 nm / min, less than 4 nm / min, or less than 3 nm / min. Note that, in the case of an oxide semiconductor film not including Poly-OS, the etching rate when the oxide semiconductor film is etched using a 0.5% hydrofluoric acid solution at room temperature is 15 nm / min or more. Here, "40°C" includes a range of 40±5°C and may be the temperature of the etching solution or the set temperature of the etching solution. "Room temperature" refers to 25±5°C.

[0048] An example of the oxide semiconductor layer 140 is shown in Table 1. Table 1 shows the etching rates of each prepared sample with respect to a mixed acid etching solution (mixed acid AT-2F manufactured by Rasa Kogyo Co., Ltd.) and a 0.5% hydrofluoric acid solution. When each sample was etched, the temperature of the mixed acid etching solution was 40° C., and the temperature of the 0.5% hydrofluoric acid solution was room temperature (22° C.). In Table 1, Sample 1 is an oxide semiconductor layer 140 containing Poly-OS, Sample 2 is an oxide semiconductor film having an amorphous structure before heat treatment, and Sample 3 is an oxide semiconductor film containing indium gallium zinc oxide (IGZO) with an indium ratio of less than 50%.

[0049] [Table 1]

[0050] As shown in Table 1, Sample 1 (oxide semiconductor layer 140 containing Poly-OS) is hardly etched using a mixed acid etching solution, and is etched at only 2 nm / min at most using a 0.5% hydrofluoric acid solution. Sample 1 has an etching rate of 1 / 100 or less with a mixed acid etching solution and approximately 1 / 10 or less with a 0.5% hydrofluoric acid solution than Sample 2 (oxide semiconductor film having an amorphous structure before heat treatment). Sample 1 also has an etching rate of 1 / 100 or less with a mixed acid etching solution than Sample 3 (oxide semiconductor film containing IGZO with an indium ratio of less than 50%). That is, Sample 1 is significantly more etch-resistant than Samples 2 and 3.

[0051] Such excellent etching resistance of the oxide semiconductor layer 140 containing Poly-OS is a property that cannot be obtained from a conventional oxide semiconductor having a polycrystalline structure that is fabricated by a process at or below 500° C. Although the detailed mechanism of the excellent etching resistance of the oxide semiconductor layer 140 containing Poly-OS is unclear, it is believed that Poly-OS has a polycrystalline structure different from the conventional one.

[0052] As described above, the oxide semiconductor layer 140 containing Poly-OS has a very low etching rate with respect to an etching solution. Therefore, it is very difficult to pattern the oxide semiconductor layer 140. Therefore, when forming the island-shaped oxide semiconductor layer 140, an oxide semiconductor film having an amorphous structure before heat treatment is patterned into islands, and then the oxide semiconductor film is crystallized by heat treatment. In this way, the island-shaped oxide semiconductor layer 140 containing Poly-OS can be formed.

[0053] [4. Configuration of second gate electrode 190] When the Poly-OS contains many oxygen defects, carriers are generated. Also, when hydrogen is trapped in the oxygen defects, carriers are generated. Thus, the Poly-OS containing oxygen defects and hydrogen has electrical conductivity. Also, the conductive Poly-OS has light-transmitting properties. Therefore, the conductive Poly-OS can be used as a transparent conductive material. In this embodiment, the second gate electrode 190 is made of a conductive Poly-OS. The second gate electrode 190 can be made of a material similar to that of the oxide semiconductor layer 140. That is, the second gate electrode 190 is made of an oxide semiconductor containing two or more metal elements including indium (In). Also, the second gate electrode 190 has a polycrystalline structure.

[0054] Although the details will be described later, the second gate electrode 190 including the conductive Poly-OS can be formed by generating oxygen defects and supplying hydrogen. The sheet resistance of the second gate electrode 190 is 1000Ω / sq. or less, preferably 500Ω / sq. or less, and more preferably 250Ω / sq. or less. The film thickness of the second gate electrode 190 is, for example, 30 nm to 200 nm, preferably 50 nm to 180 nm, and more preferably 100 nm to 150 nm. If the film thickness of the second gate electrode 190 is less than 30 nm, the resistance of the second gate electrode 190 is not sufficiently reduced. If the film thickness of the second gate electrode 190 is more than 200 nm, the second gate electrode 190 may include a region where no oxygen defects are generated, and the resistance of the second gate electrode 190 may not be sufficiently reduced. Therefore, the film thickness of the second gate electrode 190 is preferably within the above range.

[0055] [4. Method for Manufacturing Semiconductor Device 10] A method for manufacturing the semiconductor device 10 will be described with reference to FIGS.

[0056] Fig. 5 is a flowchart for explaining a method for manufacturing the semiconductor device 10 according to one embodiment of the present invention. Fig. 6 to Fig. 16 are schematic cross-sectional views for explaining a method for manufacturing the semiconductor device 10 according to one embodiment of the present invention. Each step of the flowchart shown in Fig. 5 will be described in order below.

[0057] In step S100, a first conductive film CF1 is formed on a first substrate 100 by sputtering (see FIG. 6).

[0058] In step S110, the first conductive film CF1 is patterned by photolithography to form the first gate electrodes 110 and the scanning lines 120 (see FIG. 7).

[0059] In step S120, the first insulating layer 130 is formed by CVD to cover the first gate electrode 110 and the scanning line 120 (see FIG. 8).

[0060] In step S130, the oxide semiconductor film OS1 is formed on the first insulating layer 130 by sputtering. The conditions for forming the oxide semiconductor film OS1 are as described above. Since the oxide semiconductor film OS1 has an amorphous structure, it is easy to etch the oxide semiconductor film OS1. Therefore, the oxide semiconductor film OS1 is patterned by photolithography (see FIG. 9).

[0061] In step S140, the oxide semiconductor film OS1 is subjected to a first heat treatment under the conditions described above. The first heat treatment crystallizes the oxide semiconductor film OS1, and an oxide semiconductor layer 140 including Poly-OS is formed (see FIG. 10).

[0062] In step S150, a first opening OP1 is formed in the first insulating layer 130 by photolithography (see FIG. 11). In the first opening OP1, a part of the scanning line 120 is exposed.

[0063] In step S160, a second conductive film CF2 that covers the oxide semiconductor layer 140 and the first opening OP1 is formed by sputtering (see FIG. 12). For example, the second conductive film CF2 is a laminated film containing titanium and aluminum (Ti / Al / Ti film).

[0064] In step S170, the second conductive film CF2 is patterned by photolithography to form the source electrode 150, the drain electrode 160, and the connection electrode 170 (see FIG. 13). The source electrode 150 and the drain electrode 160 are in contact with the oxide semiconductor layer 140, and the connection electrode 170 is in contact with the scanning line 120 through the first opening OP1. The second conductive film CF2 is preferably etched by wet etching using an etching solution. As described above, the oxide semiconductor layer 140 containing Poly-OS has excellent etching resistance. Therefore, when the second conductive film CF2 is etched using an etching solution, the oxide semiconductor layer 140 is hardly etched. Therefore, in the oxide semiconductor layer 140, the difference between the film thickness of the first region in contact with one of the source electrode 150 and the drain electrode and the film thickness of the second region not in contact with the source electrode 150 and the drain electrode is 3 nm or less. By adjusting the etching conditions, it is possible to set the difference in film thickness between the first region and the second region to 2 nm or less, preferably 1 nm or less, and more preferably 0.5 nm or less.

[0065] In step S180, the second insulating layer 180 is formed by CVD. Furthermore, the second opening OP2 is formed in the second insulating layer 180 by photolithography. In the second opening OP2, a part of the connection electrode 170 is exposed.

[0066] In step S190, the oxide semiconductor film OS2 is formed on the second insulating layer 180 by sputtering. The conditions for forming the oxide semiconductor film OS2 are as described above. Since the oxide semiconductor film OS2 has an amorphous structure, it is easy to etch the oxide semiconductor film OS2. Therefore, the oxide semiconductor film OS2 is patterned by photolithography (see FIG. 15).

[0067] In step S200, a second heat treatment is performed on the oxide semiconductor layer 140 and the oxide semiconductor film OS2. Oxygen defects may be generated in the oxide semiconductor layer 140 due to a process after the formation of the oxide semiconductor layer 140. However, by performing the second heat treatment, oxygen is supplied from the first insulating layer 130 and the second insulating layer 180 to the oxide semiconductor layer 140, and the oxygen defects are repaired. In particular, in the second heat treatment, since the oxide semiconductor film OS2 is formed on the second insulating layer 180 so as to overlap with the oxide semiconductor layer 140, the oxide semiconductor film OS2 suppresses the oxygen in the second insulating layer 180 from being released to the outside, and oxygen can be efficiently supplied to the oxide semiconductor layer 140. Meanwhile, the oxide semiconductor film OS2 is crystallized by the second heat treatment, and a second gate electrode 190 including Poly-OS is formed (see FIG. 16). However, the second gate electrode 190 formed in step S200 may not have a sufficiently low resistance. Therefore, in order to reduce the resistance of the second gate electrode 190, step S210 is performed.

[0068] In step S210, the nitride layer 200 is formed by using a CVD method, a sputtering method, or an ALD method. Silicon nitride is preferably used as the nitride layer 200. Silicon nitride is formed by using a CVD method, but oxygen defects are generated in the second gate electrode 190 by reactive gases present in the chamber. In addition, many gases used in the CVD method contain hydrogen, and a lot of hydrogen is present in the chamber during film formation. Furthermore, the first substrate 100 is heated in the CVD method. Therefore, when silicon nitride is formed on the second gate electrode 190 in step S210, oxygen defects are generated in the second gate electrode 190, and hydrogen is diffused into the second gate electrode 190 and trapped in the oxygen defects. This sufficiently reduces the resistance of the second gate electrode 190. Note that when the second gate electrode 190 is not sufficiently reduced in resistance by only forming the nitride layer 200, a heat treatment may be performed after step S210. Since the second gate electrode 190 is in contact with the nitride layer 200, oxygen in the second gate electrode 190 is extracted by the nitride layer 200 by the heat treatment, and oxygen defects are generated in the second gate electrode 190. Furthermore, hydrogen contained in the nitride layer 200 is diffused into the second gate electrode 190 by the heat treatment. This further reduces the resistance of the second gate electrode 190.

[0069] Through the above steps, the semiconductor device 10 shown in Figures 3 and 4 is manufactured. The semiconductor device 10 thus manufactured has a size of 30 cm 2 / Vs or higher.

[0070] According to the semiconductor device 10, since the second gate electrode 190 has light-transmitting properties, it is possible to suppress a decrease in the aperture ratio of the pixel PX. Furthermore, according to the manufacturing method of the semiconductor device 10, it is possible to repair oxygen defects in the oxide semiconductor layer 140 including Poly-OS and reduce the resistance of the second gate electrode 190 including Poly-OS by a single heat treatment. This makes it possible to suppress the manufacturing cost of the semiconductor device 10. Furthermore, as can be understood from the fact that the oxide semiconductor layer 140 includes Poly-OS and has excellent etching resistance, it has stable properties not only during the manufacturing of the semiconductor device 10 but also after the manufacturing. Therefore, the semiconductor device 10 has high reliability.

[0071] <Modification 1 of the First Embodiment> 17 to 19, a modified method for manufacturing the semiconductor device 10 will be described. Note that in the following, description of configurations similar to those of the semiconductor device 10 may be omitted.

[0072] Fig. 17 is a flow chart for explaining a method for manufacturing a semiconductor device 10 according to an embodiment of the present invention. Fig. 18 and Fig. 19 are schematic cross-sectional views for explaining a method for manufacturing a semiconductor device 10 according to an embodiment of the present invention. Each step of the flow chart shown in Fig. 17 will be explained in order below.

[0073] Steps S100 to S190 are similar to those described with reference to Fig. 5, and therefore description thereof will be omitted here. In this modification, step S210 is carried out after step S190.

[0074] In step S210, the nitride layer 200 is formed by using a CVD method, a sputtering method, or an ALD method (see FIG. 18). In step S210 of this modification, the nitride layer 200 is formed on the oxide semiconductor film OS2 having an amorphous structure. By forming the nitride layer 200, oxygen defects are generated in the oxide semiconductor film OS2, and hydrogen is trapped in the generated oxygen defects. After step S210, step S200 is performed.

[0075] In step S200, a second heat treatment is performed on the oxide semiconductor layer 140 and the oxide semiconductor film OS2. In the second heat treatment, since the oxide semiconductor film OS2 is formed on the second insulating layer 180 so as to overlap with the oxide semiconductor layer 140, the oxide semiconductor film OS2 suppresses oxygen in the second insulating layer 180 from being released to the outside, and oxygen can be efficiently supplied to the oxide semiconductor layer 140. Meanwhile, the oxide semiconductor film OS2 is crystallized by the second heat treatment, and the second gate electrode 190 including the Poly-OS is formed (see FIG. 19). In step S200 of this modification, hydrogen is trapped in the oxygen defects of the oxide semiconductor film OS2, so that the oxygen defects are difficult to repair. Therefore, the second gate electrode 190 has a low resistance.

[0076] Through the above steps, the semiconductor device 10 shown in Figures 3 and 4 is manufactured. The semiconductor device 10 thus manufactured is also a 30 cm 2 / Vs or higher.

[0077] In the semiconductor device 10 manufactured in this modification, the second gate electrode 190 has light-transmitting properties, so that the aperture ratio of the pixel PX can be prevented from decreasing. According to the manufacturing method of the semiconductor device 10 in this modification, oxygen defects in the oxide semiconductor layer 140 including Poly-OS can be repaired and the resistance of the second gate electrode 190 including Poly-OS can be reduced by a single heat treatment. This reduces the manufacturing cost of the semiconductor device 10. Furthermore, as can be understood from the fact that the oxide semiconductor layer 140 includes Poly-OS and has excellent etching resistance, the oxide semiconductor layer 140 has stable properties not only during the manufacturing of the semiconductor device 10 but also after the manufacturing. Therefore, the semiconductor device 10 has high reliability.

[0078] <Modification 2 of the First Embodiment> 20 and 21, another modified example of the method for manufacturing the semiconductor device 10 will be described. Note that in the following, description of configurations similar to those of the semiconductor device 10 may be omitted.

[0079] Fig. 20 is a flowchart for explaining a method for manufacturing the semiconductor device 10 according to one embodiment of the present invention. Fig. 21 is a schematic cross-sectional view for explaining a method for manufacturing the semiconductor device 10 according to one embodiment of the present invention. Each step of the flowchart shown in Fig. 20 will be described in order below.

[0080] Steps S100 to S190 and step S210 are similar to the steps explained with reference to Fig. 17, and therefore explanations will be omitted here. In this modification, step S220 is carried out after step S210.

[0081] In step S220, an impurity element is added to the oxide semiconductor film OS2 by using an ion implantation method to form an oxide semiconductor film OS3 containing the impurity element and having an amorphous structure (see FIG. 21). The impurity element is added to the oxide semiconductor film OS2 via the nitride layer 200. For example, the impurity element is boron (B) or phosphorus (P), but is not limited thereto. Oxygen defects are generated in the oxide semiconductor film OS3 to which the impurity element is added. After step S220, step S200 is performed.

[0082] In step S200, a second heat treatment is performed on the oxide semiconductor layer 140 and the oxide semiconductor film OS3. The second heat treatment crystallizes the oxide semiconductor film OS2 to form a second gate electrode 190 including Poly-OS. The second gate electrode 190 includes an impurity element. Oxygen defects are generated, and in the Poly-OS including the impurity element, the oxygen defects are not easily repaired by the impurity element. In addition, hydrogen is trapped in the oxygen defects, so that the oxygen defects in the Poly-OS are stabilized. Therefore, the conductivity of the second gate electrode 190 including the Poly-OS including the impurity element is stable.

[0083] Through the above steps, the semiconductor device 10 shown in Figures 3 and 4 is manufactured. The semiconductor device 10 thus manufactured is also a 30 cm 2 / Vs or higher.

[0084] In the semiconductor device 10 manufactured in this modification, the second gate electrode 190 has light-transmitting properties, so that the aperture ratio of the pixel PX can be suppressed from decreasing. According to the manufacturing method of the semiconductor device 10 in this modification, oxygen defects in the oxide semiconductor layer 140 including Poly-OS can be repaired and the resistance of the second gate electrode 190 including Poly-OS can be reduced by a single heat treatment. This reduces the manufacturing cost of the semiconductor device 10. As can be understood from the fact that the oxide semiconductor layer 140 includes Poly-OS and has excellent etching resistance, the properties of the oxide semiconductor layer 140 are stable not only during the manufacturing of the semiconductor device 10 but also after the manufacturing. Furthermore, the conductivity of the second gate electrode 190 is stable. Therefore, the semiconductor device 10 has high reliability.

[0085] <Modification 3 of the First Embodiment> 22 and 23, a semiconductor device 10A that is a modified example of the semiconductor device 10 will be described. Note that in the following, description of configurations similar to those of the semiconductor device 10 may be omitted.

[0086] Fig. 22 is a schematic plan view showing the configuration of a semiconductor device 10A according to one embodiment of the present invention. Fig. 23 is a schematic plan view showing the configuration of a semiconductor device 10A according to one embodiment of the present invention.

[0087] In a plan view, the second gate electrode 190A is located between the source electrode 150 and the drain electrode 160. The second gate electrode 190A is spaced from the source electrode 150 by a gap g. s and a gap g from the drain electrode 160 d Here, the gap g s is the distance from one end face of the second gate electrode 190 to the end face of the source electrode 150, and the gap g d is the distance from the other end face of the second gate electrode 190 to the end face of the drain electrode 160. s is the gap g d may be the same as the gap g d The gap g may be different froms and gap g d Each of the gaps g is 0.1 μm or more and 2.0 μm or less, preferably 0.3 μm or more and 1.5 μm or less, and more preferably 0.5 μm or more and 1.0 μm or less. s and gap g d By providing the second gate electrode 190A with the source electrode 150 or the drain electrode 160, it is possible to suppress the occurrence of an inter-electrode short circuit between the second gate electrode 190A and the source electrode 150 or the drain electrode 160. In the semiconductor device 10A, the first gate electrode 110 is disposed between the gap g s and gap g d However, the gap g s and gap g d If each of the gaps g is smaller than 0.1 μm, a short circuit between the second gate electrode 190A and the source electrode 150 or the drain electrode 160 is likely to occur. s and gap g d If each of the gaps g is greater than 2.0 μm, the current flowing through the channel decreases, and the field effect mobility decreases. s and gap g d The range is preferably within the above range.

[0088] As described above, in order to suppress the occurrence of inter-electrode short circuit between the second gate electrode 190A and the source electrode 150 or the drain electrode 160, the second gate electrode 190A does not overlap with the source electrode 150 and the drain electrode 160 in a plan view. As shown in FIG. 22, the second gate electrode 190A extends so as to surround an end of the drain electrode 160. Note that the second gate electrode 190A only needs to extend so as to surround one end of the source electrode 150 and the drain electrode 160 and be electrically connected to the scanning line 120.

[0089] According to the semiconductor device 10A, even if the second gate electrode 190A surrounds the end of the source electrode 150 or the drain electrode 160 in a plan view and the area of ​​the non-overlapping region is large, the second gate electrode 190A has light transmission, so that the decrease in the aperture ratio of the pixel PX can be suppressed. In addition, the second gate electrode 190A is arranged with a gap between the source electrode 150 and the drain electrode 160 without overlapping with them in a plan view, so that the occurrence of short circuits between the electrodes can be suppressed. Therefore, the semiconductor device 10B has high reliability.

[0090] <Fourth Modification of the First Embodiment> 24, a semiconductor device 10B that is another modified example of the semiconductor device 10 will be described. Note that in the following, description of configurations similar to those of the semiconductor device 10 may be omitted.

[0091] FIG. 24 is a schematic plan view showing the configuration of a semiconductor device 10B according to one embodiment of the present invention.

[0092] The semiconductor device 10B includes a plurality of oxide semiconductor layers 140 (a first oxide semiconductor layer 140-1, a second oxide semiconductor layer 140-2, and a third oxide semiconductor layer 140-3). Each of the first oxide semiconductor layer 140-1 to the third oxide semiconductor layer 140-3 is formed in an island shape. That is, the first oxide semiconductor layer 140-1 to the third oxide semiconductor layer 140-3 are arranged separately from each other. In the semiconductor device 10B having high field effect mobility, a large current flows through a channel formed in the oxide semiconductor layer 140, so that the oxide semiconductor layer 140 may generate heat. In particular, the heat generation of the oxide semiconductor layer 140 becomes more noticeable as the area of ​​the oxide semiconductor layer 140 becomes larger. Therefore, by reducing the area of ​​one oxide semiconductor layer 140 and arranging a plurality of oxide semiconductor layers 140, it is possible to suppress the heat generation from the oxide semiconductor layer 140 while maintaining the amount of current flowing through the channel.

[0093] According to the semiconductor device 10B, since the second gate electrode 190 has light transmitting properties, it is possible to suppress a decrease in the aperture ratio of the pixel PX. Furthermore, in the semiconductor device 10B, it is possible to suppress heat generation in the oxide semiconductor layer 140. Therefore, the semiconductor device 10B has high reliability.

[0094] <Second embodiment> The crystallinity of the Poly-OS can be controlled by using a buffer layer. In this embodiment, a semiconductor device 11 including a buffer layer will be described. In the following description, the description of the same configuration as that of the semiconductor device 10 may be omitted.

[0095] [1. Configuration of semiconductor device 11] With reference to FIG. 25, a semiconductor device 11 according to an embodiment of the present invention will be described.

[0096] FIG. 25 is a schematic cross-sectional view showing the configuration of a semiconductor device 11 according to one embodiment of the present invention.

[0097] As shown in FIG. 25, the semiconductor device 11 includes a first substrate 100, a first gate electrode 110, a scanning line 120, a first insulating layer 130, an oxide semiconductor layer 140, a source electrode 150, a drain electrode 160, a connection electrode 170, a second insulating layer 180, a metal oxide layer 210, a second gate electrode 190, and a nitride layer 200. The metal oxide layer 210 is provided on the second insulating layer 180, overlapping with the oxide semiconductor layer 140. The second insulating layer 180 and the metal oxide layer 210 have a second opening OP2 through which a part of the upper surface of the connection electrode 170 is exposed. The second gate electrode 190 is provided on the metal oxide layer 210 and in contact with the metal oxide layer 210. The second gate electrode 190 has approximately the same planar shape as the metal oxide layer 210. That is, the end face of the second gate electrode 190 approximately coincides with the end face of the metal oxide layer 210. The second gate electrode 190 is in contact with the connection electrode 170 through the second opening OP2. The nitride layer 200 covers an end face of the metal oxide layer 210 and an upper surface and an end face of the second gate electrode 190, and is provided on the second insulating layer 180.

[0098] The metal oxide layer 210 can function as a buffer layer that improves the crystallinity of the Poly-OS included in the second gate electrode 190. The second gate electrode 190 including the Poly-OS with improved crystallinity has a further reduced resistance.

[0099] For example, a metal oxide containing aluminum as a main component is used as the metal oxide layer 210. The ratio of aluminum contained in the metal oxide layer 210 may be 5% to 70%, 10% to 60%, or 30% to 50% of the entire metal oxide layer 210. The above ratio may be a mass ratio or a weight ratio.

[0100] The thickness of the metal oxide layer 210 is 1 nm or more and 10 nm or less, preferably 1 nm or more and 5 nm or less. Aluminum oxide is preferably used as the metal oxide layer 210. Aluminum oxide has high barrier properties against gases such as oxygen and hydrogen. Here, the barrier properties refer to the function of suppressing the permeation of gases such as oxygen and hydrogen.

[0101] Note that a metal oxide containing a metal other than aluminum as a main component may be used as the metal oxide layer 210. For example, indium tin oxide (ITO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), or the like may be used as the metal oxide layer 210.

[0102] [2. Method for Manufacturing Semiconductor Device 11] A method for manufacturing the semiconductor device 11 will be described with reference to FIGS.

[0103] Fig. 26 is a flowchart for explaining a method for manufacturing the semiconductor device 11 according to one embodiment of the present invention. Fig. 27 to Fig. 31 are schematic cross-sectional views for explaining a method for manufacturing the semiconductor device 11 according to one embodiment of the present invention. Each step of the flowchart shown in Fig. 26 will be described in order below.

[0104] Steps S100 to S170 are similar to those described in the first embodiment with reference to Fig. 5, and therefore will not be described here. In the manufacture of the semiconductor device 11, step S181 is carried out after step S170.

[0105] In step S181, the second insulating layer 180 and the metal oxide film MO are formed in this order (see FIG. 27). The second insulating layer 180 is formed by using a CVD method. The metal oxide film MO is formed by using a sputtering method or an atomic layer deposition method (ALD method). For example, the second insulating layer 180 includes silicon oxide, and the silicon oxide is in contact with the oxide semiconductor layer 140. Also, for example, aluminum oxide is used as the metal oxide film MO. After step S181, step S182 is performed.

[0106] In step S182, a second opening OP2 is formed in the second insulating layer 180 and the metal oxide film MO by photolithography (see FIG. 28). A part of the connection electrode 170 is exposed in the second opening OP2. After step S182, step S190 is performed.

[0107] In step S190, the oxide semiconductor film OS2 is formed on the metal oxide film MO by sputtering. The conditions for forming the oxide semiconductor film OS2 are as described above. Since the oxide semiconductor film OS2 has an amorphous structure, it is easy to etch the oxide semiconductor film OS2. Therefore, the oxide semiconductor film OS2 is patterned by photolithography (see FIG. 29). The oxide semiconductor film OS2 is in contact with the connection electrode through the second opening OP2. After step S190, step S200 is performed.

[0108] In step S200, a second heat treatment is performed on the oxide semiconductor layer 140 and the oxide semiconductor film OS2. In the second heat treatment, since the metal oxide film MO covering the second insulating layer 180 is formed, the metal oxide film MO suppresses oxygen in the second insulating layer 180 from being released to the outside, and oxygen can be efficiently supplied to the oxide semiconductor layer 140. In addition, the oxide semiconductor film OS2 is crystallized by the second heat treatment, and the second gate electrode 190 including Poly-OS is formed (see FIG. 30). The metal oxide film MO functions as a buffer layer, and the crystallinity of the second gate electrode 190 is controlled. Specifically, the size of the crystal grains included in the second gate electrode 190 increases, and the crystallinity of the second gate electrode 190 increases. After step S200, step S230 is performed.

[0109] In step S230, the metal oxide film MO is patterned using the second gate electrode 190 as a mask to form the metal oxide layer 210 (see FIG. 31). The second gate electrode 190 including Poly-OS has excellent etching resistance. Therefore, even when the metal oxide film MO is etched in the patterning of the metal oxide film MO, the second gate electrode 190 used as a mask is not etched. In the semiconductor device 11, the second gate electrode 190 can be used as a mask in the formation of the metal oxide layer 210, so that a photolithography process can be omitted. After step S230, step S210 is performed.

[0110] In step S210, the nitride layer 200 is formed by CVD, sputtering, or ALD. Oxygen defects are generated in the second gate electrode 190, and hydrogen is diffused into the second gate electrode 190 and trapped in the oxygen defects. This allows the second gate electrode 190 to have a sufficiently low resistance.

[0111] Through the above steps, the semiconductor device 11 shown in FIG. 25 is manufactured. The semiconductor device 11 manufactured in this manner has a size of 30 cm 2 / Vs or higher.

[0112] In the semiconductor device 11, since the second gate electrode 190 has light-transmitting properties, it is possible to suppress a decrease in the aperture ratio of the pixel PX. Furthermore, in the manufacturing method of the semiconductor device 11, it is possible to repair oxygen defects in the oxide semiconductor layer 140 including Poly-OS and reduce the resistance of the second gate electrode 190 including Poly-OS in a single heat treatment. This makes it possible to suppress the manufacturing cost of the semiconductor device 10. Furthermore, the crystallinity of the second gate electrode 190 is increased and stabilized by the metal oxide layer 210. Therefore, the semiconductor device 11 has high reliability.

[0113] <Modification of the second embodiment> 32 to 39, a semiconductor device 11C which is a modified example of the semiconductor device 11 will be described. Note that, in the following, description of configurations similar to those of the semiconductor device 10 may be omitted. In addition, in the following, for convenience of description, the connection electrode 170 described in the first embodiment will be described as the first connection electrode 170.

[0114] [1. Configuration of semiconductor device 11C] Fig. 32 is a schematic plan view showing the configuration of a semiconductor device 11C according to one embodiment of the present invention. Fig. 33 is a schematic cross-sectional view showing the configuration of a semiconductor device 11C according to one embodiment of the present invention. Fig. 33 is a cross-sectional view of the semiconductor device 11C taken along line B1-B2 in Fig. 32.

[0115] As shown in FIG. 33, the semiconductor device 11C includes a first substrate 100, a first gate electrode 110, a scanning line 120, a first insulating layer 130, an oxide semiconductor layer 140, a source electrode 150, a drain electrode 160, a first connection electrode 170, a second insulating layer 180, a metal oxide layer 210C, a second gate electrode 190C, a nitride layer 200, a third insulating layer 220, and a second connection electrode 230. The metal oxide layer 210C is provided on the second insulating layer 180, overlapping with the oxide semiconductor layer 140. The second gate electrode 190C is provided on the metal oxide layer 210C in contact with the metal oxide layer 210C. The second gate electrode 190C has approximately the same planar shape as the metal oxide layer 210C. That is, the end face of the second gate electrode 190C approximately coincides with the end face of the metal oxide layer 210C. In a plan view, the metal oxide layer 210C and the second gate electrode 190C do not overlap with the first connection electrode 170. The nitride layer 200 covers the end face of the metal oxide layer 210C and the upper face and end face of the second gate electrode 190C, and is provided on the second insulating layer 180. The third insulating layer 220 is provided on the nitride layer 200. The second insulating layer 180, the nitride layer 200, and the third insulating layer 220 have a second opening OP2 through which a part of the upper face of the first connection electrode 170 is exposed. In addition, the nitride layer 200 and the third insulating layer 220 have a third opening OP3 through which a part of the upper face of the second gate electrode 190 is exposed. The second connection electrode 230 is provided on the third insulating layer 220. The second connection electrode 230 is in contact with the first connection electrode 170 through the second opening OP2, and is in contact with the second gate electrode 190C through the third opening OP3.

[0116] As shown in FIG. 32, the second gate electrode 190C is provided apart from the first connection electrode 170. However, as described above, the second connection electrode 230 is in contact with the first connection electrode 170 and the second gate electrode 190C. Therefore, the second gate electrode 190C is electrically connected to the first gate electrode 110 via the first connection electrode 170 and the second connection electrode 230. Therefore, the voltage included in the signal input to the scanning line 120 is applied to both the first gate electrode 110 and the second gate electrode 190C.

[0117] The third insulating layer 220 can function as an interlayer insulating layer. For example, the same material as the first insulating layer 130 and the second insulating layer 180 can be used as the third insulating layer 220. The third insulating layer 220 can also function as a planarizing layer. In this case, for example, a resin such as polyimide or acrylic can be used as the third insulating layer 220. The resin may be a photosensitive resin. When a photosensitive resin is used as the third insulating layer 220, etching can be performed by directly exposing the photosensitive resin to light without applying a resist, so that the process using the photolithography method is simplified. The third insulating layer 220 may have a single layer structure or a laminated structure. When the third insulating layer 220 has a laminated structure, the third insulating layer 220 may have a structure in which a resin is laminated on an oxide or a nitride.

[0118] The second connection electrode 230 has electrical conductivity. The second connection electrode 230 can be made of the same material as the first connection electrode 170. The second connection electrode 230 can also be made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). The second connection electrode 230 is provided so as to overlap not only the source electrode 150 or the drain electrode 160 but also the scanning line 120, so that the aperture ratio of the pixel PX is hardly decreased. Therefore, the second connection electrode 230 can be made of not only a material having light-transmitting properties but also a material having no light-transmitting properties.

[0119] [2. Method for Manufacturing Semiconductor Device 11C] A method for manufacturing the semiconductor device 11C will be described with reference to FIGS.

[0120] Fig. 34 is a flowchart for explaining a method for manufacturing a semiconductor device 11C according to one embodiment of the present invention. Figs. 35 to 39 are schematic cross-sectional views for explaining a method for manufacturing a semiconductor device 11C according to one embodiment of the present invention. Each step of the flowchart shown in Fig. 34 will be described in order below.

[0121] Steps S100 to S170 and step S181 are similar to the steps explained with reference to Fig. 26, and therefore explanations will be omitted here. In the manufacture of the semiconductor device 11C, step S190 is carried out after step S170.

[0122] In step S190, the oxide semiconductor film OS2 is formed on the metal oxide film MO by sputtering. The conditions for forming the oxide semiconductor film OS2 are as described above. Since the oxide semiconductor film OS2 has an amorphous structure, it is easy to etch the oxide semiconductor film OS2. Therefore, the oxide semiconductor film OS2 is patterned by photolithography (see FIG. 35). After step S190, step S200 is performed.

[0123] In step S200, a second heat treatment is performed on the oxide semiconductor layer 140 and the oxide semiconductor film OS2. In the second heat treatment, since the metal oxide film MO covering the second insulating layer 180 is formed, the metal oxide film MO suppresses the oxygen in the second insulating layer 180 from being released to the outside, and oxygen can be efficiently supplied to the oxide semiconductor layer 140. In addition, the oxide semiconductor film OS2 is crystallized by the second heat treatment, and the second gate electrode 190C including Poly-OS is formed (see FIG. 36). The metal oxide film MO functions as a buffer layer, and the crystallinity of the second gate electrode 190C is controlled. Specifically, the size of the crystal grains included in the second gate electrode 190C increases, and the crystallinity of the second gate electrode 190C increases. After step S200, step S230 is performed.

[0124] In step S230, the metal oxide film MO is patterned using the second gate electrode 190C as a mask to form a metal oxide layer 210C (see FIG. 37). The second gate electrode 190C including Poly-OS has excellent etching resistance. Therefore, even when the metal oxide film MO is etched in the patterning of the metal oxide film MO, the second gate electrode 190C used as a mask is not etched. In the semiconductor device 11C, the second gate electrode 190C can be used as a mask in the formation of the metal oxide layer 210C, so that a photolithography process can be omitted. After step S230, step S210 is performed.

[0125] In step S210, a nitride layer 200 is formed by CVD, sputtering, or ALD (see FIG. 38). Oxygen defects are generated in the second gate electrode 190C, and hydrogen is diffused into the second gate electrode 190C and trapped in the oxygen defects. This allows the second gate electrode 190C to have a sufficiently low resistance. After step S210, step S240 is performed.

[0126] In step S240, the third insulating layer 220 is formed on the second insulating layer 180 by using a coating method. In addition, a second opening OP2 penetrating the second insulating layer 180, the nitride layer 200, and the third insulating layer 220 and a third opening OP3 penetrating the nitride layer 200 and the third insulating layer 220 are formed by using a photolithography method (see FIG. 39). When the third insulating layer 220 has photosensitivity, the second opening OP2 and the third opening OP3 can be formed without using a photoresist. In the second opening OP2, a part of the first connection electrode 170 is exposed. In the third opening OP3, a part of the second gate electrode 190C is exposed. After step S240, step S250 is performed.

[0127] In step S250, a fourth conductive film is formed on the third insulating layer 220 by sputtering, and the fourth conductive film is patterned by photolithography to form the second connection electrode 230. The second connection electrode 230 is in contact with the first connection electrode 170 through the second opening OP2, and in contact with the second gate electrode 190C through the third opening OP3.

[0128] Through the above steps, the semiconductor device 11C shown in Figures 32 and 33 is manufactured. The semiconductor device 11C manufactured in this manner has a size of 30 cm 2 / Vs or higher.

[0129] In the semiconductor device 11C, since the second gate electrode 190 has light-transmitting properties, it is possible to suppress a decrease in the aperture ratio of the pixel PX. In addition, in the manufacturing method of the semiconductor device 11C, it is possible to repair oxygen defects in the oxide semiconductor layer 140 including Poly-OS and reduce the resistance of the second gate electrode 190 including Poly-OS in a single heat treatment. This makes it possible to suppress the manufacturing cost of the semiconductor device 10. Furthermore, the crystallinity of the second gate electrode 190 is increased and stabilized by the metal oxide layer 210. Therefore, the semiconductor device 11C has high reliability.

[0130] The above-described embodiments of the present invention may be combined as appropriate as long as they are not mutually inconsistent. Furthermore, those in which a person skilled in the art appropriately adds or removes components or modifies designs, or adds or omits steps or modifies conditions based on the embodiments, are also included in the scope of the present invention as long as they include the gist of the present invention.

[0131] Even if there are other effects and advantages different from those brought about by the aspects of each of the above-mentioned embodiments, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention. [Explanation of symbols]

[0132] 1: display device, 2: display unit, 3: light source unit, DP: display section, DRV: driving element, FPC: flexible wiring board, GD: scanning line driving circuit, GL: scanning line, PX: pixel, SD: signal line driving circuit, SL: signal line, TP: terminal section, 10, 10A, 10B, 11, 11C: semiconductor device, 20: liquid crystal element, 100: first substrate, 110: first gate electrode, 120: scanning line, 130: first insulating layer, 140: oxide semiconductor layer, 140-1: first oxide semiconductor layer, 140-2: second oxide semiconductor layer, 140-3: third oxide semiconductor layer, 150: source electrode, 160: drain electrode, 170: connection electrode (first connection electrode), 180: second insulating layer, 190, 190A, 190C: second gate electrode, 200: nitride layer, 210, 210C: metal oxide layer, 220: third insulating layer, 230: second connection electrode, 300: second substrate, CF1: first conductive film, CF2: second conductive film, MO: metal oxide film, OP1: first opening, OP2: second opening, OP3: third opening, OS1, OS2, OS3: oxide semiconductor film

Claims

1. A first gate electrode; an oxide semiconductor layer including a first oxide semiconductor having a polycrystalline structure on the first gate electrode; a source electrode and a drain electrode electrically connected to the oxide semiconductor layer; a second gate electrode on the source electrode and the drain electrode, the second gate electrode overlapping with the first gate electrode and the oxide semiconductor layer; the second gate electrode includes a second oxide semiconductor having a polycrystalline structure; the second gate electrode is electrically connected to the first gate electrode.

2. 2. The semiconductor device according to claim 1, wherein the sheet resistance of the second gate electrode is 1000 Ω / sq. or less.

3. The semiconductor device according to claim 1 , wherein the second gate electrode overlaps with at least one of the source electrode and the drain electrode in a plan view.

4. 2 . The semiconductor device according to claim 1 , wherein said second gate electrode is disposed with a gap from each of said source electrode and said drain electrode in a plan view.

5. The semiconductor device according to claim 4 , wherein, in the plan view, the second gate electrode extends so as to surround one end of each of the source electrode and the drain electrode.

6. 2. The semiconductor device according to claim 1, further comprising a metal oxide layer below said second gate electrode and in contact with said second gate electrode.

7. a connection electrode on the second gate electrode and in contact with the second gate electrode; 7. The semiconductor device according to claim 6, wherein said second gate electrode is electrically connected to said first gate electrode via said connection electrode.

8. The oxide semiconductor layer is a first region in contact with one of the source electrode and the drain electrode; a second region overlapping the second gate electrode between the source electrode and the drain electrode; 2. The semiconductor device according to claim 1, wherein a difference between a film thickness of said first region and a film thickness of said second region is 3 nm or less.

9. 2 . The semiconductor device according to claim 1 , wherein an etching rate of the oxide semiconductor layer when the oxide semiconductor layer is etched at 40° C. with an etching solution containing phosphoric acid as a main component is less than 3 nm / min.

10. The semiconductor device according to claim 9 , wherein the etching solution contains nitric acid and acetic acid.

11. the oxide semiconductor layer is formed by performing a heat treatment on an oxide semiconductor film having an amorphous structure; The semiconductor device according to claim 9 , wherein an etching rate when the oxide semiconductor film is etched using the etching solution at 40° C. is 100 nm / min or more.

12. 2 . The semiconductor device according to claim 1 , wherein the oxide semiconductor layer is etched at a rate of less than 5 nm / min using a 0.5% hydrofluoric acid solution at room temperature.

13. each of the oxide semiconductor layer and the second gate electrode contains a plurality of metal elements; one of the metal elements is indium; The semiconductor device according to claim 1 , wherein an atomic ratio of said indium to said plurality of metal elements is 50% or more.

14. forming a first gate electrode; forming an oxide semiconductor layer including a first oxide semiconductor having a polycrystalline structure on the first gate electrode; forming a source electrode and a drain electrode in contact with the oxide semiconductor layer; forming a first oxide semiconductor film on the source electrode and the drain electrode; performing a heat treatment on the first oxide semiconductor film to form a second gate electrode including a second oxide semiconductor having a polycrystalline structure; forming a nitride layer covering the second gate electrode.

15. The oxide semiconductor layer is a first region in contact with one of the source electrode and the drain electrode; a second region overlapping the second gate electrode between the source electrode and the drain electrode; 15. The method of claim 14, wherein a difference between a film thickness of the first region and a film thickness of the second region is 3 nm or less.

16. 15. The method for manufacturing a semiconductor device according to claim 14, wherein an etching rate when the oxide semiconductor layer is etched at 40° C. using an etching solution containing phosphoric acid as a main component is less than 3 nm / min.

17. The method for manufacturing a semiconductor device according to claim 16, wherein the etching solution contains nitric acid and acetic acid.

18. the oxide semiconductor layer is formed by performing a heat treatment on an oxide semiconductor film having an amorphous structure; The method for manufacturing a semiconductor device according to claim 16 , wherein an etching rate when the oxide semiconductor film is etched using the etching solution at 40° C. is 100 nm / min or more.

19. 15. The method for manufacturing a semiconductor device according to claim 14, wherein an etching rate when the oxide semiconductor layer is etched with a 0.5% hydrofluoric acid solution at room temperature is less than 5 nm / min.

20. each of the oxide semiconductor layer and the second gate electrode contains a plurality of metal elements; one of the metal elements is indium; The method for manufacturing a semiconductor device according to claim 14 , wherein an atomic ratio of said indium to said plurality of metal elements is 50% or more.

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