Semiconductor device

Abstract

To provide a semiconductor device in which light deterioration is suppressed.SOLUTION: A semiconductor device includes a light-blocking layer, a first silicon nitride insulating layer having a first interface and being in contact with the light-blocking layer, a first silicon oxide insulating layer having a second interface and being in contact with the first silicon nitride insulating layer, an oxide semiconductor layer on the first silicon oxide insulating layer, a second silicon oxide insulating layer on the oxide semiconductor layer, a gate electrode on the second silicon oxide insulating layer, and a second silicon nitride insulating layer on the gate electrode. In a plan view, the entire channel region of the oxide semiconductor layer overlaps with the light-blocking layer. The first silicon oxide insulating layer is in contact with the second silicon oxide insulating layer. The film thickness t (nm) of the first silicon nitride insulating layer satisfies the condition that when the light with a wavelength of 450 nm enters the first silicon nitride insulating layer at an angle of 60 degrees from a normal direction of the second interface, the light reflected on the first interface and the light reflected on the second interface weaken each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a semiconductor device that uses an oxide semiconductor film as a channel. [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] Since an oxide semiconductor film transmits light in the visible light region, a semiconductor device including the oxide semiconductor film is less susceptible to photodegradation than a semiconductor device including a silicon semiconductor film. However, it is desired to further suppress photodegradation in a semiconductor device including an oxide semiconductor film.

[0005] An object of one embodiment of the present invention is to provide a semiconductor device in which photodegradation is suppressed. [Means for solving the problem]

[0006] A semiconductor device according to one embodiment of the present invention includes a light-shielding layer, a first silicon nitride insulating layer on the light-shielding layer and having a first interface in contact with the light-shielding layer, a first silicon oxide insulating layer on the first silicon nitride insulating layer and having a second interface in contact with the first silicon nitride insulating layer, an oxide semiconductor layer on the first silicon oxide insulating layer including a channel region, a source region, and a drain region, a second silicon oxide insulating layer on the oxide semiconductor layer, a gate electrode on the second silicon oxide insulating layer, and the second silicon nitride insulating layer on the gate electrode, wherein in a plan view, the entire channel region overlaps with the light-shielding layer, the first silicon oxide insulating layer is in contact with the second silicon oxide insulating layer, and a thickness t (nm) of the first silicon nitride insulating layer satisfies a condition for the light reflected at the first interface and the light reflected at the second interface to weaken each other when light having a wavelength of 450 nm is incident on the first silicon nitride insulating layer at an angle of 60 degrees from a normal to the second interface. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Diagram 2] 1 is a schematic plan view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Diagram 3] 1 is a flowchart showing a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 4]1A to 1C are schematic cross-sectional views showing a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Diagram 5] 1A to 1C are schematic cross-sectional views showing 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 showing 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 showing 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 showing 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 showing 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 showing a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 11] 1 is a schematic cross-sectional view showing a configuration of a semiconductor device according to an embodiment of the present invention; [Figure 12] 1A to 1C are schematic cross-sectional views showing 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 showing 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 showing 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 showing 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 showing a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 17] 1 is a graph showing the variation of threshold voltage in an NBTIS test with respect to the thickness of the first silicon nitride insulating layer and the thickness of the first silicon oxide insulating layer 120. [Figure 18] 11 is a simulation result of reflectance showing the incidence angle dependence of a first silicon nitride insulating layer. 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, 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 "electro-optical layer" may include a liquid crystal layer, an electroluminescent (EL) layer, an electrochromic (EC) layer, and an electrophoretic layer, unless technically inconsistent. Therefore, in the embodiment, a liquid crystal display device including a liquid crystal layer and an organic EL display device including an organic EL layer are exemplified as the display device. However, the structure described in the embodiment can be applied to the display device including the other electro-optical layers described above.

[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 A semiconductor device 10 according to one embodiment of the present invention will be described with reference to FIGS.

[0016] [1. Configuration of Semiconductor Device 10] The configuration of a semiconductor device 10 according to one embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a schematic cross-sectional view showing the configuration of the semiconductor device 10 according to one embodiment of the present invention. Fig. 2 is a schematic plan view showing the configuration of a semiconductor device according to one embodiment of the present invention. Specifically, Fig. 1 is a cross-sectional view taken along line A-A' in Fig. 2.

[0017] As shown in FIG. 1, the semiconductor device 10 includes a substrate 100, a light-shielding layer 105, a first silicon nitride insulating layer 110, a first silicon oxide insulating layer 120, an oxide semiconductor layer 140, a second silicon oxide insulating layer 150, a gate electrode 160, a second silicon nitride insulating layer 170, a third silicon oxide insulating layer 180, a source electrode 201, and a drain electrode 203. The light-shielding layer 105 is provided on the substrate 100. The first silicon nitride insulating layer 110 covers the upper surface and end surface of the light-shielding layer 105 and is provided on the substrate 100. The first silicon oxide insulating layer 120 is provided on the first silicon nitride insulating layer 110. The oxide semiconductor layer 140 is provided on the first silicon oxide insulating layer 120. The second silicon oxide insulating layer 150 covers the upper surface and end surface of the oxide semiconductor layer 140 and is provided on the first silicon oxide insulating layer 120. The gate electrode 160 overlaps with the oxide semiconductor layer 140 and is provided on the second silicon oxide insulating layer 150. The second silicon nitride insulating layer 170 covers the upper surface and end surfaces of the gate electrode 160 and is provided on the second silicon oxide insulating layer 150. The third silicon oxide insulating layer 180 is provided on the second silicon nitride insulating layer 170. The second silicon oxide insulating layer 150, the second silicon nitride insulating layer 170, and the third silicon oxide insulating layer 180 are provided with openings 171 and 173 through which a part of the upper surface of the oxide semiconductor layer 140 is exposed. The source electrode 201 is provided on the third silicon oxide insulating layer 180 and inside the opening 171, and is in contact with the oxide semiconductor layer 140. Similarly, the drain electrode 203 is provided on the third silicon oxide insulating layer 180 and inside the opening 173, and is in contact with the oxide semiconductor layer 140. In the following description, when there is no particular need to distinguish between the source electrode 201 and the drain electrode 203, they may be collectively referred to as the source-drain electrode 200.

[0018] The oxide semiconductor layer 140 is divided into a source region S, a drain region D, and a channel region CH with respect to the gate electrode 160. That is, the oxide semiconductor layer 140 includes the channel region CH overlapping with the gate electrode 160, and the source region S and the drain region D not overlapping with the gate electrode 160. In the film thickness direction of the oxide semiconductor layer 140, the end of the channel region CH is approximately coincident with the end of the gate electrode 160. The channel region CH has a semiconductor property. Each of the source region S and the drain region D has a conductor property. Therefore, the electrical conductivity of the source region S and the drain region D is larger than the electrical conductivity of the channel region CH. The source electrode 201 and the drain electrode 203 are in contact with the source region S and the drain region D, respectively, and are electrically connected to the oxide semiconductor layer 140. The oxide semiconductor layer 140 may have a single-layer structure or a multilayer structure.

[0019] 2, each of the light-shielding layer 105 and the gate electrode 160 has a certain width in the D1 direction and extends in the D2 direction perpendicular to the D1 direction. In the D1 direction, the width of the light-shielding layer 105 is larger than the width of the gate electrode 160. Also, the entire channel region CH overlaps with the light-shielding layer 105. In the semiconductor device 10, the D1 direction corresponds to the direction in which a current flows from the source electrode 201 to the drain electrode 203 through the oxide semiconductor layer 140. Therefore, the length of the channel region CH in the D1 direction is the channel length L, and the width of the channel region CH in the D2 direction is the channel width W.

[0020] The substrate 100 can support each layer constituting the semiconductor device 10. For example, a rigid substrate having light-transmitting properties, such as a glass substrate, a quartz substrate, or a sapphire substrate, can be used as the substrate 100. A rigid substrate having no light-transmitting properties, such as a silicon substrate, can also be used as the substrate 100. A flexible substrate having light-transmitting properties, such as a polyimide resin substrate, an acrylic resin substrate, a siloxane resin substrate, or a fluororesin substrate, can also be used as the substrate 100. In order to improve the heat resistance of the substrate 100, impurities may be introduced into the above-mentioned resin substrate. Note that a substrate in which a silicon oxide film or a silicon nitride film is formed on the above-mentioned rigid substrate or flexible substrate can also be used as the substrate 100.

[0021] The light-shielding layer 105 can reflect or absorb external light. As described above, the light-shielding layer 105 is provided to have an area larger than the channel region CH of the oxide semiconductor layer 140, and therefore can block external light incident on the channel region CH from the substrate 100 side. A metal material can be used for the light-shielding layer 105. Specifically, aluminum (Al), copper (Cu), titanium (Ti), molybdenum (Mo), tungsten (W), or an alloy thereof can be used for the light-shielding layer 105. For example, the alloy used for the light-shielding layer 105 is molybdenum tungsten (MoW), but is not limited thereto.

[0022] The first silicon nitride insulating layer 110, the first silicon oxide insulating layer 120, the second silicon nitride insulating layer 170, and the third silicon oxide insulating layer 180 can prevent impurities from diffusing into the oxide semiconductor layer 140. Specifically, the first silicon nitride insulating layer 110 and the first silicon oxide insulating layer 120 can prevent the diffusion of impurities contained in the substrate 100, and the second silicon nitride insulating layer 170 and the third silicon oxide insulating layer 180 can prevent the diffusion of impurities (e.g., water, etc.) entering from the outside. For example, silicon nitride (SiN x) or silicon oxynitride (SiN x O y The first silicon oxide insulating layer 120 and the third silicon oxide insulating layer 180 may be made of silicon oxide (SiO x ) or silicon oxynitride (SiO x N y ) can be used. Here, silicon oxynitride (SiN x O y ) is a silicon compound that contains a smaller ratio of oxygen than nitrogen (x>y). Silicon oxynitride (SiO x N y ), a silicon compound that contains a smaller ratio (x>y) of nitrogen (N) than oxygen (O).

[0023] Each of the first silicon nitride insulating layer 110, the first silicon oxide insulating layer 120, the second silicon nitride insulating layer 170, and the third silicon oxide insulating layer 180 may have a planarizing function. The first silicon oxide insulating layer 120 may have a function of releasing oxygen by heat treatment. When the first silicon oxide insulating layer 120 has a function of releasing oxygen by heat treatment, oxygen is released from the first silicon oxide insulating layer 120 by the heat treatment performed in the manufacturing process of the semiconductor device 10, and the released oxygen can be supplied to the oxide semiconductor layer 140.

[0024] The gate electrode 160, the source electrode 201, and the drain electrode 203 are conductive. For example, copper (Cu), aluminum (Al), titanium (Ti), chromium (Cr), cobalt (Co), nickel (Ni), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), bismuth (Bi), or an alloy thereof can be used for each of the gate electrode 160, the source electrode 201, and the drain electrode 203. Each of the gate electrode 160, the source electrode 201, and the drain electrode 203 may have a single-layer structure or a multilayer structure.

[0025] The second silicon oxide insulating layer 150 functions as a gate insulating layer. For example, the second silicon oxide insulating layer 150 may be made of silicon oxide (SiO x ) or silicon oxynitride (SiO x N y ) can be used. The second silicon oxide insulating layer 150 preferably has a composition close to a stoichiometric ratio. The second silicon oxide insulating layer 150 preferably has few defects. Specifically, the second silicon oxide insulating layer 150 preferably has no defects observed when evaluated by electron spin resonance (ESR).

[0026] The oxide semiconductor layer 140 is made of an oxide semiconductor containing two or more metal elements including indium (In). Metal elements other than indium include gallium (Ga), zinc (Zn), aluminum (Al), hafnium (Hf), yttrium (Y), zirconium (Zr), and lanthanoids. The oxide semiconductor layer 140 may have an amorphous structure or a polycrystalline structure. However, in order to improve electrical characteristics, the oxide semiconductor layer 140 preferably has a polycrystalline structure.

[0027] When the oxide semiconductor layer 140 has 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 as the oxide semiconductor layer 140. 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 not inhibited by the gallium element, and the oxide semiconductor layer 140 has a polycrystalline structure.

[0028] A detailed manufacturing method of the oxide semiconductor layer 140 will be described later in the manufacturing method of the semiconductor device 10, but the oxide semiconductor layer 140 can be formed by sputtering. The composition of the oxide semiconductor layer 140 formed by sputtering depends on the composition of the sputtering target. When the oxide semiconductor layer 140 has a polycrystalline structure, the composition of the sputtering target and the composition of the oxide semiconductor layer 140 are substantially the same. In this case, 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. When the oxide semiconductor layer 140 has a polycrystalline structure, the composition of the oxide semiconductor film may be specified by using an X-ray diffraction (XRD) method. Specifically, the composition of the metal elements of the oxide semiconductor film can be specified based on the crystal structure and lattice constant of the oxide semiconductor film 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 varies depending on the sputtering process conditions and the like, and is not limited to the above.

[0029] As described above, the oxide semiconductor layer 140 may have an amorphous structure or a polycrystalline structure, but preferably has a polycrystalline structure. An oxide semiconductor having a polycrystalline structure can be manufactured using a Poly-OS (Polycrystalline Oxide Semiconductor) technique. In the following, an oxide semiconductor having a polycrystalline structure may be described as a Poly-OS to distinguish it from an oxide semiconductor having an amorphous structure.

[0030] The configuration of the semiconductor device 10 has been described above, but the semiconductor device 10 described above is a so-called top-gate type transistor. The semiconductor device 10 can be modified in various ways. For example, when the light-shielding layer 105 is conductive, the semiconductor device 10 may be configured such that the light-shielding layer 105 functions as a gate electrode, and the first silicon nitride insulating layer 110 and the first silicon oxide insulating layer 120 function as gate insulating layers. In this case, the semiconductor device 10 is a so-called dual-gate type transistor. When the light-shielding layer 105 is conductive, the light-shielding layer 105 may be a floating electrode or may be connected to the source electrode 201. Furthermore, the semiconductor device 10 may be a so-called bottom-gate type transistor in which the light-shielding layer 105 functions as a main gate electrode.

[0031] 2. Method for Manufacturing Semiconductor Device 10 A method for manufacturing the semiconductor device 10 according to one embodiment of the present invention will be described with reference to Fig. 3 to Fig. 10. Fig. 3 is a flowchart showing a method for manufacturing the semiconductor device 10 according to one embodiment of the present invention. Figs. 4 to 10 are schematic cross-sectional views showing a method for manufacturing the semiconductor device 10 according to one embodiment of the present invention.

[0032] 3, the method for manufacturing the semiconductor device 10 includes steps S1010 to S1110. Steps S1010 to S1110 will be described in order below, but the order of the steps may be reversed in the method for manufacturing the semiconductor device 10. Furthermore, the method for manufacturing the semiconductor device 10 may include additional steps.

[0033] In step S1010, a light-shielding layer 105 having a predetermined pattern is formed on the substrate 100. The light-shielding layer 105 is patterned by photolithography. A first silicon nitride insulating layer 110 and a first silicon oxide insulating layer 120 are formed on the light-shielding layer 105 (see FIG. 4). The first silicon nitride insulating layer 110 and the first silicon oxide insulating layer 120 are formed by CVD. For example, silicon nitride and silicon oxide are formed as the first silicon nitride insulating layer 110 and the first silicon oxide insulating layer 120, respectively. When silicon nitride is used as the first silicon nitride insulating layer 110, the first silicon nitride insulating layer 110 can block impurities diffused from the substrate 100 side to the oxide semiconductor layer 140. When silicon oxide is used as the first silicon oxide insulating layer 120, the first silicon oxide insulating layer 120 can release oxygen by heat treatment.

[0034] The light incident on the first silicon nitride insulating layer 110 is reflected not only at the interface between the light shielding layer 105 and the first silicon nitride insulating layer 110 (hereinafter referred to as the "first interface"), but also at the interface between the first silicon nitride insulating layer 110 and the first silicon oxide insulating layer 120 (hereinafter referred to as the "second interface"). Therefore, if the light intensified by the interference effect is incident on the channel region of the oxide semiconductor layer 140, the photodegradation of the oxide semiconductor layer 140 is promoted. Therefore, in the semiconductor device 10, the film thickness of the first silicon nitride insulating layer 110 is set to satisfy the condition that the light reflected at the first interface and the light reflected at the second interface weaken each other when light with a wavelength of 450 nm is incident on the first silicon nitride insulating layer at an angle of 60 degrees from the normal direction of the second interface. This makes it possible to suppress the photodegradation of the oxide semiconductor layer 140. For example, the film thickness t (nm) of the first silicon nitride insulating layer 110 is set to satisfy t=150(a-1)+b (where a is a natural number and b is a constant), where the constant b is, for example, 75±12.5.

[0035] There is no particular limitation on the thickness of the first silicon oxide insulating layer 120. For example, the thickness of the first silicon oxide insulating layer 120 is greater than the thickness of the first silicon nitride insulating layer 110.

[0036] In step S1020, the oxide semiconductor film 145 is formed on the first silicon oxide insulating layer 120 (see FIG. 5). The oxide semiconductor film 145 is formed by a sputtering method. The thickness of the oxide semiconductor film 145 is, for example, 10 nm to 100 nm, preferably 15 nm to 70 nm, and more preferably 15 nm to 40 nm.

[0037] The oxide semiconductor film 145 in step S1020 is amorphous. In the Poly-OS technique, in order for the oxide semiconductor layer 140 to have a uniform polycrystalline structure in the substrate surface, it is preferable that the oxide semiconductor film 145 after film formation and before heat treatment is amorphous. Therefore, it is preferable that the film formation conditions of the oxide semiconductor film 145 are conditions under which the oxide semiconductor layer 140 immediately after film formation is not crystallized as much as possible. When the oxide semiconductor film 145 is formed by a sputtering method, the oxide semiconductor film 145 is formed while controlling the temperature of the film formation target (the substrate 100 and the layer formed on the substrate 100) to 100° C. or less, preferably 80° C. or less, and more preferably 50° C. or less. In addition, the oxide semiconductor film 145 is formed under a condition of low oxygen partial pressure. The oxygen partial pressure is 2% or more and 20% or less, preferably 3% or more and 15% or less, and more preferably 3% or more and less than 10%.

[0038] In step S1030, the oxide semiconductor film 145 is patterned (see FIG. 6). The oxide semiconductor film 145 is patterned by photolithography. The oxide semiconductor film 145 may be etched by wet etching or dry etching. In the wet etching, an acidic etchant may be used. As the etchant, for example, oxalic acid, PAN, sulfuric acid, hydrogen peroxide solution, or hydrofluoric acid may be used.

[0039] In step S1040, a heat treatment is performed on the oxide semiconductor film 145. Hereinafter, the heat treatment performed in step S1040 is referred to as "OS annealing". In the OS annealing, the oxide semiconductor film 145 is held at a predetermined target temperature for a predetermined time. The predetermined target temperature is 300° C. or more and 500° C. or less, and preferably 350° C. or more and 450° C. or less. The holding time at the target temperature is 15 minutes or more and 120 minutes or less, and preferably 30 minutes or more and 60 minutes or less. The OS annealing crystallizes the oxide semiconductor film 145, and the oxide semiconductor layer 140 having a polycrystalline structure (i.e., the oxide semiconductor layer 140 including Poly-OS) is formed.

[0040] The oxide semiconductor layer containing Poly-OS has excellent etching resistance. Specifically, the oxide semiconductor layer 140 has a very small etching rate when etched using an etching solution for wet etching. This means that the oxide semiconductor layer 140 is hardly etched by the etching solution. 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”), the etching rate 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, the oxide semiconductor film 145 having an amorphous structure before heat treatment, when the oxide semiconductor film 145 is etched using a mixed acid etching solution at 40° C., the etching rate 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 the oxide semiconductor film 145 not including Poly-OS, the etching rate when the oxide semiconductor film 145 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. Furthermore, "room temperature" refers to 25±5°C.

[0041] An example of the etching rate 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., in which the ratio of phosphoric acid in the mixed acid etching solution is 65%) 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. In Table 1, Sample 1 is an oxide semiconductor layer 140 containing Poly-OS, Sample 2 is an oxide semiconductor film 145 having an amorphous structure before heat treatment, and Sample 3 is an oxide semiconductor film containing indium gallium zinc oxide (IGZO) in which the ratio of indium is less than 50%.

[0042] [Table 1]

[0043] 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 145 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.

[0044] 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.

[0045] In step S1050, the second silicon oxide insulating layer 150 is formed on the oxide semiconductor layer 140 (see FIG. 7). The second silicon oxide insulating layer 150 is formed by using a CVD method. For example, silicon oxide is formed as the second silicon oxide insulating layer 150. In order to reduce defects in the second silicon oxide insulating layer 150, the second silicon oxide insulating layer 150 may be formed at a film formation temperature of 350° C. or higher. The thickness of the second silicon oxide insulating layer 150 is 50 nm or more and 300 nm or less, preferably 60 nm or more and 200 nm or less, and more preferably 70 nm or more and 150 nm or less. After the second silicon oxide insulating layer 150 is formed, a process of introducing oxygen into a part of the second silicon oxide insulating layer 150 may be performed.

[0046] The second silicon oxide insulating layer 150 contacts the first silicon oxide insulating layer 120. The total thickness of the first silicon oxide insulating layer 120 and the second silicon oxide insulating layer 150 is preferably greater than the thickness of the first silicon nitride insulating layer.

[0047] In step S1060, a heat treatment is performed on the oxide semiconductor layer 140. Hereinafter, the heat treatment performed in step S1060 is referred to as "oxidation annealing." When the second silicon oxide insulating layer 150 is formed on the oxide semiconductor layer 140, many oxygen defects are generated on the upper surface and side surfaces of the oxide semiconductor layer 140. When the oxidation annealing is performed, oxygen is supplied from the first silicon oxide insulating layer 120 and the second silicon oxide insulating layer 150 to the oxide semiconductor layer 140, and the oxygen defects are repaired.

[0048] In step S1070, a gate electrode 160 having a predetermined pattern is formed on the second silicon oxide insulating layer 150 (see FIG. 8). The gate electrode 160 is formed by sputtering or atomic layer deposition, and the gate electrode 160 is patterned by photolithography.

[0049] In step S1080, a source region S and a drain region D are formed in the oxide semiconductor layer 140 (see FIG. 8). The source region S and the drain region D are formed by ion implantation. Specifically, impurities are implanted into the oxide semiconductor layer 140 through the second silicon oxide insulating layer 150 using the gate electrode 160 as a mask. For example, argon (Ar), phosphorus (P), boron (B), or the like is used as the implanted impurity. In the source region S and the drain region D that do not overlap with the gate electrode 160, oxygen vacancies are generated by the ion implantation, and hydrogen is trapped in the generated oxygen vacancies. This reduces the resistance of the source region S and the drain region D. On the other hand, in the channel region that overlaps with the gate electrode 160, impurities are not implanted, so that oxygen vacancies are not generated and the resistance of the channel region CH does not decrease.

[0050] In the semiconductor device 10, since impurities are implanted into the oxide semiconductor layer 140 through the second silicon oxide insulating layer 150, the second silicon oxide insulating layer 150 may also contain impurities such as argon (Ar), phosphorus (P), or boron (B).

[0051] In step S1090, the second silicon nitride insulating layer 170 and the third silicon oxide insulating layer 180 are formed on the second silicon oxide insulating layer 150 and the gate electrode 160 (see FIG. 9). The second silicon nitride insulating layer 170 and the third silicon oxide insulating layer 180 are formed by using a CVD method. For example, silicon oxide and silicon nitride are formed as the second silicon nitride insulating layer 170 and the third silicon oxide insulating layer 180, respectively. The thickness of the second silicon nitride insulating layer 170 is 50 nm or more and 500 nm or less. The thickness of the third silicon oxide insulating layer 180 is also 50 nm or more and 500 nm or less.

[0052] In step S1100, openings 171 and 173 are formed in the second silicon oxide insulating layer 150, the second silicon nitride insulating layer 170, and the third silicon oxide insulating layer 180 (see FIG. 10). By forming the openings 171 and 173, the source region S and the drain region D of the oxide semiconductor layer 140 are exposed.

[0053] In step S1110, a source electrode 201 is formed on the third silicon oxide insulating layer 180 and inside the opening 171, and a drain electrode 203 is formed on the third silicon oxide insulating layer 180 and inside the opening 173. The source electrode 201 and the drain electrode 203 are formed as the same layer. Specifically, the source electrode 201 and the drain electrode 203 are formed by patterning one conductive film that has been deposited. Through the above steps, the semiconductor device 10 shown in FIG. 1 is manufactured.

[0054] Although the manufacturing method of the semiconductor device 10 has been described above, the manufacturing method of the semiconductor device 10 is not limited to this.

[0055] In the semiconductor device 10 according to this embodiment, the thickness of the first silicon nitride insulating layer 110 in contact with the light-shielding layer 105 is set to a value based on predetermined conditions, thereby making it possible to suppress photodegradation.

[0056] <Second embodiment> A semiconductor device 20 according to one embodiment of the present invention will be described with reference to Figures 11 to 16. When the components of the semiconductor device 20 are similar to those of the semiconductor device 10, the description of the components of the semiconductor device 20 may be omitted.

[0057] [1. Configuration of Semiconductor Device 20] The configuration of a semiconductor device 20 according to one embodiment of the present invention will be described with reference to Fig. 11. Fig. 11 is a schematic cross-sectional view showing the configuration of a semiconductor device 20 according to one embodiment of the present invention. Specifically, Fig. 11 is a cross-sectional view taken along line A-A' in Fig. 2.

[0058] 11, the semiconductor device 10 includes a substrate 100, a light-shielding layer 105, a first silicon nitride insulating layer 110, a first silicon oxide insulating layer 120, a metal oxide layer 130, an oxide semiconductor layer 140, a second silicon oxide insulating layer 150, a gate electrode 160, a second silicon nitride insulating layer 170, a third silicon oxide insulating layer 180, a source electrode 201, and a drain electrode 203. The metal oxide layer 130 is provided on the first silicon oxide insulating layer 120. The oxide semiconductor layer 140 is provided on the metal oxide layer 130. An end face of the metal oxide layer 130 is substantially aligned with an end face of the oxide semiconductor layer 140.

[0059] The metal oxide layer 130 can promote the crystallization of the oxide semiconductor layer 140. Therefore, when the metal oxide layer 130 is provided, the oxide semiconductor layer 140 is likely to contain Poly-OS. For example, aluminum oxide (AlO x ) or aluminum oxide nitride (AlO x N y ) etc. can be used.

[0060] 2. Method for Manufacturing Semiconductor Device 20 A method for manufacturing a semiconductor device 20 according to an embodiment of the present invention will be described with reference to Figs. 12 to 16. Fig. 12 is a flowchart showing a method for manufacturing a semiconductor device 20 according to an embodiment of the present invention. Figs. 13 to 16 are schematic cross-sectional views showing a method for manufacturing a semiconductor device 20 according to an embodiment of the present invention. The method for manufacturing a semiconductor device 20 includes steps S2010 to S2120. Steps S2010 to S2120 will be described in order below, but the order of the steps may be changed in the method for manufacturing a semiconductor device 10. Furthermore, the method for manufacturing a semiconductor device 10 may include further steps.

[0061] Step S2010 is similar to step S1010, and therefore the description of step S2010 will be omitted.

[0062] In step S2020, a metal oxide film 135 and an oxide semiconductor film 145 are sequentially formed on the first silicon oxide insulating layer 120 (see FIG. 13). The metal oxide film 135 is formed by a sputtering method. The thickness of the metal oxide film 135 is, for example, 1 nm or more and 10 nm or less, preferably 1 nm or more and 5 nm or less. Note that the oxide semiconductor film 145 formed on the metal oxide film 135 is amorphous.

[0063] Step S2030 is the same as step S1030. That is, the oxide semiconductor film 145 is patterned (see FIG. 14).

[0064] Step S2040 is similar to step S1040, and therefore the description of step S2040 will be omitted.

[0065] In step S2050, the metal oxide film 135 is patterned to form the metal oxide layer 130 (see FIG. 15). The oxide semiconductor layer 140 containing Poly-OS is sufficiently crystallized by the OS annealing and has high etching resistance. Therefore, even if the oxide semiconductor layer 140 containing Poly-OS is used as a mask when the metal oxide film 135 is patterned, the oxide semiconductor layer 140 does not disappear. Therefore, in the Poly-OS technique, the metal oxide layer 130 can be etched using the patterned oxide semiconductor layer 140 containing Poly-OS as a mask. By etching the metal oxide film 135 using the oxide semiconductor layer 140 as a mask, the photolithography process can be omitted. In this case, the end face of the metal oxide layer 130 is approximately the same as the end face of the oxide semiconductor layer 140. The metal oxide film 135 may be etched by wet etching or dry etching. For example, diluted hydrofluoric acid (DHF) is used for wet etching.

[0066] Step S2060 is similar to step S1050. That is, the second silicon oxide insulating layer 150 is formed so as to cover the upper surface and end surfaces of the oxide semiconductor layer 140 and the end surfaces of the metal oxide layer 130 (see FIG. 16).

[0067] Steps S2070 to S2120 are similar to steps S1060 to S1110, and therefore the description of steps S2070 to S2120 will be omitted.

[0068] Although the method for manufacturing the semiconductor device 20 has been described above, the method for manufacturing the semiconductor device 20 is not limited to this.

[0069] In the semiconductor device 20 according to this embodiment, the thickness of the first silicon nitride insulating layer 110 in contact with the light-shielding layer 105 is set to a value based on predetermined conditions, thereby making it possible to suppress photodegradation. EXAMPLES

[0070] The semiconductor device 20 will be described in further detail based on the fabricated sample.

[0071] [1. Preparation of samples] As samples, a semiconductor device 20 was fabricated on a glass substrate using the manufacturing method described in the second embodiment. Specifically, a plurality of samples were fabricated with different thicknesses of the first silicon nitride insulating layer 110 (25 nm, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, 250 nm, 275 nm, 300 nm) and the first silicon oxide insulating layer 120 (50 nm, 100 nm, 200 nm). The fabrication conditions for the other layers were the same, and the main materials and film thickness fabrication conditions are shown in Table 2.

[0072] [Table 2]

[0073] [2. Sample evaluation] [2-1. Electrical characteristics] The initial electrical characteristics of each sample were measured. The conditions for measuring the electrical characteristics are shown in Table 3. For the measurement of the electrical characteristics, a sample having a channel width W / channel length L = 4.5 μm / 3.0 μm was used. In addition, the S value and field effect mobility (linear field effect mobility in the linear region) of each sample were calculated from the electrical characteristics.

[0074] [Table 3]

[0075] [2-2.NBTIS Examination] In order to evaluate the light degradation of each sample, a negative bias temperature illumination stress (NBTIS) test was performed. In the NBTIS test, the semiconductor device 20 is irradiated with light for a predetermined time, and the light degradation of the semiconductor device 20 can be evaluated according to the magnitude of change in the threshold voltage of the semiconductor device 20 before and after the light irradiation. Specifically, when the light degradation of the semiconductor device 20 is large, the fluctuation amount of the threshold voltage of the semiconductor device 20 also becomes large. The light irradiation conditions of the NBTIS test are shown in Table 3. In the NBTIS test, a sample having a channel width W / channel length L=4.5 μm / 3.0 μm was used, and the electrical characteristics of the sample after light irradiation were measured under the measurement conditions shown in Table 4.

[0076] [Table 4]

[0077] Fig. 17 is a graph showing the variation of threshold voltage in an NBTIS test with respect to the thickness of the first silicon nitride insulating layer 110 and the thickness of the first silicon oxide insulating layer 120. The horizontal axis of Fig. 17 shows the thickness of the first silicon nitride insulating layer 110, and the vertical axis of Fig. 17 shows the variation of threshold voltage in an NBTIS test. In Fig. 17, the plotted points for each thickness of the first silicon oxide insulating layer 120 are connected.

[0078] 17, the variation in threshold voltage of semiconductor device 20 shows a periodic tendency with respect to the film thickness of first silicon nitride insulating layer 110. More specifically, in semiconductor device 20, the variation in threshold voltage decreases for approximately every 150 nm of the film thickness of first silicon nitride insulating layer 110. Moreover, the variation in threshold voltage of semiconductor device 20 does not depend on the film thickness of first silicon oxide insulating layer 120.

[0079] The periodicity of the threshold fluctuation amount of the semiconductor device 20 shown in FIG. 17 depends on the film thickness of the first silicon nitride insulating layer 110, so it is considered that the optical interference effect occurs due to the film thickness of the first silicon nitride insulating layer 110. Therefore, in order to investigate the influence of the optical interference effect by the first silicon nitride insulating layer 110, a simulation of the reflectance when the incident angle (angle from the normal direction of the second interface) of the light incident on the first silicon nitride insulating layer 110 is changed was performed. In the simulation, an element consisting of the first silicon oxide insulating layer 120 / first silicon nitride insulating layer 110 / light shielding layer 105 / glass was used, and calculations were performed assuming that the incident light of a wavelength of 400 to 500 nm is reflected at the first interface and the second interface. Note that, as shown in FIG. 17, since the film thickness dependency of the first silicon oxide insulating layer 120 is not observed, calculations were performed assuming that the light is incident from the first silicon oxide insulating layer 120. In other words, the calculation was performed assuming that the film thickness of the first silicon oxide insulating layer 120 was infinite.

[0080] Fig. 18 shows simulation results of reflectance showing the incidence angle dependency of the first silicon nitride insulating layer 110. Fig. 18 shows the reflectance at incidence angles of 0 degrees, 30 degrees, and 60 degrees.

[0081] As shown in FIG. 18, periodicity of the reflectance is observed at all of the incident angles of 0 degrees, 30 degrees, and 60 degrees. Moreover, as the incident angle changes from 0 degrees to 60 degrees, the period of the periodicity of the reflectance becomes larger. In particular, when the incident angle is 60 degrees, the period is 150 nm, which coincides with the period of the threshold voltage fluctuation amount in the NBTIS test shown in FIG. 17. Specifically, in FIG. 18, the reflectance becomes minimum when the film thickness of the first silicon nitride insulating layer 110 is about 75 nm and about 225 nm, and also in FIG. 17, the fluctuation amount of the threshold voltage becomes minimum when the film thickness of the first silicon nitride insulating layer 110 is about 75 nm and about 225 nm.

[0082] The above results show that the amount of variation in threshold voltage in the NBTIS test can be suppressed by setting the film thickness of the first silicon nitride insulating layer 110 so that the reflectance of light with a wavelength of 450 nm incident on the second interface at 60 degrees is minimized. That is, the film thickness of the first silicon nitride insulating layer 110 satisfies the condition that the light reflected at the first interface and the light reflected at the second interface weaken each other when light with a wavelength of 450 nm is incident on the first silicon nitride insulating layer at 60 degrees from the normal direction of the second interface, thereby suppressing the photodegradation of the semiconductor device 20.

[0083] For example, based on this embodiment, the film thickness t (nm) of the first silicon nitride insulating layer 110 is set to satisfy t=150(a-1)+b (where a is a natural number and b is a constant). Here, the constant b is, for example, 75±12.5. The value ±12.5 of the constant b is an error, and corresponds to 1 / 2 of 25 nm, which is the number of steps in the measurement or simulation. In this manner, the error may be calculated from the number of steps.

[0084] In this embodiment, the evaluation using the sample of the semiconductor device 20 has been described, but the same applies to the semiconductor device 10.

[0085] 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.

[0086] Even if there are other effects and advantages different from those brought about by the aspects of each of the above-mentioned embodiments, those which are clear from the description in this specification or which 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]

[0087] 10, 20: semiconductor device, 100: substrate, 105: light shielding layer, 110: first silicon nitride insulating layer, 120: first silicon oxide insulating layer, 130: metal oxide layer, 135: metal oxide film, 140: oxide semiconductor layer, 145: oxide semiconductor film, 150: second silicon oxide insulating layer, 160: gate electrode, 170: second silicon nitride insulating layer, 171: opening, 173: opening, 180: third silicon oxide insulating layer, 200: source / drain electrode, 201: source electrode, 203: drain electrode

Claims

1. A light-shielding layer; a first silicon nitride insulating layer on the light-shielding layer, the first silicon nitride insulating layer having a first interface and in contact with the light-shielding layer; a first silicon oxide insulating layer on the first silicon nitride insulating layer, the first silicon oxide insulating layer having a second interface with the first silicon nitride insulating layer; an oxide semiconductor layer on the first silicon oxide insulating layer, the oxide semiconductor layer including a channel region, a source region, and a drain region; a second silicon oxide insulating layer on the oxide semiconductor layer; a gate electrode on the second silicon oxide insulating layer; a second silicon nitride insulating layer over the gate electrode; the channel region is entirely overlapped with the light-shielding layer in a plan view, the first silicon oxide insulating layer is in contact with the second silicon oxide insulating layer; a thickness t (nm) of the first silicon nitride insulating layer satisfies a condition under which, when light having a wavelength of 450 nm is incident on the first silicon nitride insulating layer at an angle of 60 degrees from a normal direction to the second interface, light reflected at the first interface and light reflected at the second interface weaken each other.

2. 2. The semiconductor device according to claim 1, wherein said thickness t (nm) of said first silicon nitride insulating layer satisfies t=150(a-1)+b (where a is a natural number and b is a constant).

3. 3. The semiconductor device according to claim 2, wherein said b is 75±12.

5.

4. 2. The semiconductor device according to claim 1, wherein the thickness of said first silicon oxide insulating layer is greater than the thickness t (nm) of said first silicon nitride insulating layer.

5. 2. The semiconductor device according to claim 1, wherein a total thickness of said first silicon oxide insulating layer and said second silicon oxide insulating layer is greater than said thickness t (nm) of said first silicon nitride insulating layer.

6. The semiconductor device of claim 1 , further comprising a metal oxide layer between the first silicon oxide insulating layer and the oxide semiconductor layer.

7. The semiconductor device according to claim 6 , wherein an end face of the metal oxide layer is substantially aligned with an end face of the oxide semiconductor layer.

8. 7. The semiconductor device according to claim 6, wherein the metal oxide layer has a thickness of 5 nm or less.

9. The semiconductor device according to claim 6 , wherein the metal oxide layer comprises aluminum oxide.

10. the oxide semiconductor layer contains a plurality of metal elements, One of the plurality of metal elements is an indium element; 2. The semiconductor device according to claim 1, wherein an atomic ratio of indium to said plurality of metal elements is 50% or more.

11. The semiconductor device according to claim 1 , wherein the oxide semiconductor layer has a polycrystalline structure.

12. 2. The semiconductor device according to claim 1, wherein said source region and said drain region contain one element selected from the group consisting of boron, phosphorus, argon, and nitrogen.

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