Display device

Abstract

A method for manufacturing a semiconductor device, wherein a junction between a source electrode layer and a drain electrode layer, and an oxide semiconductor layer is an ohmic junction.SOLUTION: After the heat treatment, a first region having a lower oxygen concentration than the oxide semiconductor film is formed between the oxide semiconductor film and the source electrode layer, and a second region having a lower oxygen concentration than the oxide semiconductor film is formed between the oxide semiconductor film and the drain electrode layer. Since the first region and the second region have lower oxygen concentration than the oxide semiconductor film, the resistance is low and an ohmic junction can be formed.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thin film transistor formed using an oxide semiconductor layer and a manufacturing method thereof. The present invention also relates to a semiconductor device manufactured using the thin film transistor.

[0002] In this specification, a semiconductor device refers to a device that can function by utilizing semiconductor characteristics. This refers to devices in general, and electro-optical devices, semiconductor circuits, and electrical equipment are all semiconductor devices. [Background technology]

[0003] Metal oxides exist in a wide variety of forms and are used for a variety of purposes. Indium oxide is well known as It is a material that has been developed and is used as a transparent electrode material required for liquid crystal displays, etc. There are.

[0004] Some metal oxides exhibit semiconducting properties. Examples of oxides include tungsten oxide, tin oxide, indium oxide, and zinc oxide. Thin film transistors using metal oxides with such semiconducting properties as the channel formation region are already known. (Patent Documents 1 to 4, Non-Patent Document 1).

[0005] Incidentally, metal oxides include not only single-component oxides but also multi-component oxides. For example, , InGaO3(ZnO) with homologous phase m (m: natural number) is In, Ga and Z It is known as a multi-component oxide semiconductor having n (Non-Patent Documents 2 to 4).

[0006] Then, the oxide semiconductor composed of the above-mentioned In-Ga-Zn-based oxide is used as a thin film transistor. It has been confirmed that it can be used as a channel layer for transistors (Patent Document 5, Non-Patent Document 6). Documents 5 and 6). [Preliminary Technology Documents] [License]

[0007] [License 1] Special Announcement No. 60-198861 [License 2] Special Announcement No. 8-264794 [License 3] Special Notice No. 11-505377 [License 4] Special Announcement No. 2000-150900 [Patent Document 5] Special Announcement No. 2004-103957 [Non-licensed literature]

[0008] [Non-licensed Document 1] MW Prins, KO Grosse-Holz, G. Muller, JFM Cillessen, JB Giesbers, RP Weening, and RM Wolf, "A ferroelectric transparent thin-film transistor", Appl. Phys. Lett., 17 June 1996, Vol.68 p.3650-3652 [Non-licensed Document 2] M. Nakamura, N. Kimizuka, and T. Mohri, "The Phase Relations in the In2O3-Ga2ZnO4-ZnO System at 1350℃", J. Solid State Chem., 1991, Vol.93, p.298-315 [Non-licensed Document 3] N. Kimizuka, M. Isobe, and M. Nakamura, “Syntheses and Single-Crystal Data of Homologous Compounds, In2O3(ZnO)m(m=3,4, and 5), InGaO3(ZnO)3, and Ga2O3(ZnO)m(m=7,8,9, and 16) in the In2O3-ZnGa2O4-ZnO System”, J. Solid State Chem., 1995, Vol.116, p.170-178 [Non-patent document 4] Masaaki Nakamura, Noboru Kimizuka, Takahiko Mohri, Mitsumasa Isobe, "Synthesis and Crystal Structure of Homologous Phase, InFeO3(ZnO)m (m: natural number) and Its Isomorphic Compounds," Solid State Physics, 1993, Vol. 28, No. 5, pp. 317-327 [Non-Patent Document 5] K. Nomura, H. Ohta, K. Ueda, T. Kamiya, M. Hirano, and H. Hosono, "Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor", SCIENCE, 2003, Vol.300, p.1269-1272 [Non-patent document 6] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, "Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors", NATURE, 2004, Vol.432 p.488-492 Summary of the Invention [Problem to be solved by the invention]

[0009] One embodiment of the present invention is a thin film transistor having a thin film transistor with an increased off-state current or a negative threshold voltage. One of the challenges is to prevent shifts.

[0010] Further, one embodiment of the present invention is a thin film transistor including a source electrode layer and a drain electrode layer, and an oxide film. It is an object of the present invention to form an ohmic junction with a nitride semiconductor layer.

[0011] Furthermore, one embodiment of the present invention is a thin film transistor having a thin film transistor having a high off-state current or a low threshold voltage. One of the objectives is to efficiently fabricate high-performance thin-film transistors that prevent phase shift. Let's say.

[0012] Furthermore, one embodiment of the present invention is a thin film transistor having a thin film transistor having a high off-state current or a low threshold voltage. and a source electrode layer and a drain electrode layer of the thin film transistor, High-performance thin-film transistors with ohmic junctions to the oxide semiconductor layer can be efficiently fabricated. One of the objectives is to produce

[0013] Another object of one embodiment of the present invention is to provide a high-quality or highly reliable semiconductor device. It shall be one. [Means for solving the problem]

[0014] One embodiment of the present invention is a method for manufacturing a semiconductor device including: providing a buffer layer over an oxide semiconductor layer; The thin film transistor is an inverted staggered type thin film transistor provided with a source electrode layer and a drain electrode layer. The buffer layer is a layer including a pair of conductive layers provided on both ends of the oxide semiconductor layer and a layer including a the conductive layer has the same metal element as the pair of conductive layers, and a metal oxide layer, which is an insulator or semiconductor, sandwiched between the pair of conductive layers and has the highest oxygen concentration; , has.

[0015] In addition to the above structure, the buffer layer may be formed on both ends of the oxide semiconductor layer. A pair of oxide semiconductor layers having a reduced oxygen concentration and the pair of oxide semiconductor layers having a reduced oxygen concentration and a pair of conductive layers containing oxygen at a high concentration provided thereon. This is one aspect of the invention.

[0016] In this specification, an insulator is defined as an insulating material having an electrical resistivity of 10 6 (Ω·m) or more A semiconductor is a material whose electrical resistivity is 10 -3 (Ω m) or more, 10 6 Less than (Ω·m) A conductor is a material whose electrical resistivity is 10 -3 (Ω·m) It will be decided.

[0017] In one embodiment of the present invention, a metal oxide layer is formed in the same step as an oxide semiconductor layer. a method for manufacturing a thin film transistor by performing oxidation treatment on a conductive layer formed on the substrate; Note that the oxidation treatment is performed on the same layer as that used to form the source electrode layer and the drain electrode layer. The resist is used as a mask. Therefore, both ends of the conductive layer are As a result, the pair of conductive layers and the pair of conductive layers are not oxidized and remain. A metal oxide layer sandwiched between conductive layers is formed.

[0018] In one embodiment of the present invention, a metal oxide layer is formed in the same step as an oxide semiconductor layer. The electrode layer is then subjected to an oxidation treatment, and a pair of high-oxygen-containing electrodes are then formed. The conductive layer and the pair of oxide semiconductor layers with reduced oxygen concentration are subjected to heat treatment to form a conductive film in which oxygen is diffused. This is a method for manufacturing a thin film transistor by forming the thin film transistor.

[0019] Another embodiment of the present invention is a conductive film including a metal oxide layer, a pair of conductive layers containing oxygen at a high concentration, and A pair of oxide semiconductor layers having a reduced oxygen concentration is formed by thermal oxidation treatment. This is a method for manufacturing a thin film transistor.

[0020] Another embodiment of the present invention is a conductive film including a metal oxide layer, a pair of conductive layers containing oxygen at a high concentration, and The pair of oxide semiconductor layers with reduced oxygen concentrations are subjected to oxidation treatment and thermal oxidation treatment. This is a method for manufacturing a thin film transistor formed by the above method.

[0021] Another embodiment of the present invention is a thin film transistor and a semiconductor device provided over the thin film transistor. and an interlayer insulating layer. [Effects of the Invention]

[0022] One embodiment of the present invention is an inverted staggered thin film transistor, in which a central portion of an oxide semiconductor layer A metal oxide layer, which is an insulator or a semiconductor, is disposed on the metal oxide layer. It functions as a protective layer that prevents impurities (such as hydrogen or water) from penetrating into the layer. It is possible to prevent an increase in the off-state current of a thin film transistor or a negative shift in the threshold voltage. can.

[0023] Further, one embodiment of the present invention is an inverted staggered thin film transistor, A pair of high-concentration conductive layers is formed between both end portions of the oxide semiconductor layer and a pair of conductive layers provided on both end portions of the oxide semiconductor layer. The conductive layer contains oxygen and a pair of oxide semiconductor layers with a reduced oxygen concentration. The oxide semiconductor layer with a reduced oxygen concentration has a lower resistance than the oxide semiconductor layer. The junctions between the source electrode layer and the drain electrode layer and the oxide semiconductor layer are ohmic junctions. can be done.

[0024] In another embodiment of the present invention, the metal oxide layer is formed in the same step as the oxide semiconductor layer. Therefore, it is possible to efficiently form high-performance thin film transistors. This can be done.

[0025] In another embodiment of the present invention, the metal oxide layer is formed in the same step as the oxide semiconductor layer. The pair of oxide semiconductor layers formed based on the conductive layer and having a reduced oxygen concentration are This is due to the diffusion of oxygen into the thin film transistor. A diastolic acid can be formed.

[0026] Another embodiment of the present invention is a semiconductor device including a thin film transistor including an oxide semiconductor. A thin film transistor having a protective layer that prevents impurities (such as hydrogen or water) from entering the layer is used. This allows the interlayer insulating layer provided on the thin film transistor to be formed in various ways depending on the purpose. The materials and manufacturing methods can be selected. In other words, high quality or high reliability semiconductor devices can be Locations can be provided. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 2 is a cross-sectional view of a thin film transistor described in Embodiment 1. [Figure 2] 10A to 10C are cross-sectional views illustrating a manufacturing process of a thin film transistor described in Embodiment 2. [Figure 3] 10A to 10C are cross-sectional views illustrating a manufacturing process of a thin film transistor described in Embodiment 2. [Figure 4] FIG. 10 is a top view illustrating a pixel of a liquid crystal display device described in Embodiment 3. [Figure 5] FIG. 11 is a cross-sectional view illustrating a pixel of a liquid crystal display device described in Embodiment 3. [Figure 6]FIG. 10 is an equivalent circuit diagram illustrating a pixel of a liquid crystal display device described in Embodiment 3. [Figure 7] FIG. 10 is a top view illustrating a pixel of a light-emitting display device described in Embodiment 4. [Figure 8] FIG. 10 is a cross-sectional view illustrating a pixel of a light-emitting display device described in Embodiment 4. [Figure 9] FIG. 10 is an equivalent circuit diagram illustrating a pixel of a light-emitting display device described in Embodiment 4. [Figure 10] FIG. 13 is a cross-sectional view of electronic paper described in Embodiment 5. [Figure 11] FIG. 2 is a density of states diagram obtained by calculation described in Example 1. [Figure 12] FIG. 2 is a density of states diagram obtained by calculation described in Example 1. [Figure 13] FIG. 2 is a density of states diagram obtained by calculation described in Example 1. [Figure 14] 1A and 1B are diagrams showing the atomic arrangements at the bonding interface between a titanium layer and an In—Ga—Zn—O-based oxide semiconductor layer before and after heat treatment, which are calculated by the calculations described in Example 1. [Figure 15] 1A and 1B are graphs showing the titanium concentration and oxygen concentration at the bonding interface between a titanium layer and an In—Ga—Zn—O-based oxide semiconductor layer before and after heat treatment, which are calculated by the calculation described in Example 1. [Figure 16] 1A and 1B are diagrams showing the atomic arrangement at the bonding interface between a titanium oxide layer and an In—Ga—Zn—O-based oxide semiconductor layer before and after heat treatment, which are calculated by the calculation described in Example 1. [Figure 17] 1A and 1B are graphs showing the titanium concentration and oxygen concentration at the bonding interface between a titanium oxide layer and an In—Ga—Zn—O-based oxide semiconductor layer before and after heat treatment, which are calculated by calculations described in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following description, and various modifications may be made without departing from the spirit and scope of the present invention. It will be readily apparent to those skilled in the art that various modifications may be made to the details. The present invention should not be construed as being limited to the description of the following embodiments.

[0029] In addition, the size, layer thickness, or area of ​​each component shown in the drawings of each embodiment may be The figures may be exaggerated for clarity and are not necessarily limited to the scale. In addition, ordinal numbers such as "first," "second," and "third" used in this specification are not limited to the construction. It is added to avoid confusion of constituent elements and is not intended to limit the number. do.

[0030] (Embodiment 1) In this embodiment, a structure of a thin film transistor according to one embodiment of the present invention will be described with reference to FIGS. Next, the characteristics of the thin film transistor will be described.

[0031] FIG. 1(a) shows a cross-sectional view of a thin film transistor 150 formed on a substrate 100. The thin film transistor 150 includes a gate electrode layer 101 provided on a substrate 100 and a gate A gate insulating layer 102 is provided on the gate electrode layer 101, and a gate insulating layer 103 is provided on the gate insulating layer 102. and a pair of conductive films formed over the oxide semiconductor layer 103. A barrier layer having conductive layers 104a, 104b and a metal oxide layer 105 which is an insulator or a semiconductor. The buffer layer 106 and the conductive layer 104a (one of the pair of conductive layers 104a and 104b) are provided on the conductive layer 104a. The source electrode layer 107a and the conductive layer 104b (other than the pair of conductive layers 104a and 104b) The pair of conductive layers 104a and 104b are connected to each other via a drain electrode layer 107b. , 104b are provided on both ends of the oxide semiconductor layer 103, and the metal oxide layer 105 is an oxide The insulating layer 104 is provided on the central portion of the nitride semiconductor layer 103 .

[0032] In other words, the thin film transistor 150 of FIG. 1(a) has an oxide semiconductor layer 103 and a source A pair of conductive layers 104a, 104b and 104c are provided between the electrode layer 107a and the drain electrode layer 107b. and a buffer layer 106 on which a metal oxide layer 105 is provided. It is a star.

[0033] FIG. 1(b) shows a cross-sectional view of a thin film transistor 151 formed on a substrate. The thin film transistor 151 has the same structure as the thin film transistor 150 shown in FIG. 1(a) but also has an oxide A pair of oxide semiconductor layers 103 each having a reduced oxygen concentration are provided on both ends of the oxide semiconductor layer 103. and a pair of oxide semiconductor layers 108a and 108b with reduced oxygen concentrations. The semiconductor device includes a pair of conductive layers 109a and 109b containing oxygen at a high concentration.

[0034] In other words, the thin film transistor 151 of FIG. 1(b) has an oxide semiconductor layer 103 and a source A pair of conductive layers 104a and 104b is provided between the electrode layer 107a and the drain electrode layer 107b. a metal oxide layer 105, a pair of oxide semiconductor layers 108a and 108b having reduced oxygen concentrations, and and a buffer layer 11 provided with a pair of conductive layers 109a and 109b containing oxygen at a high concentration. 0 is an inverted staggered thin film transistor.

[0035] The substrate 100 is made of glass such as barium borosilicate glass or aluminoborosilicate glass. A lath substrate or the like can be used.

[0036] The gate electrode layer 101 may be made of aluminum (Al), copper (Cu), titanium (Ti), Tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr), neodymium an element selected from neodymium (Nd), scandium (Sc), an alloy containing the above elements; Alternatively, nitrides containing the above elements can be used. A laminated structure can also be applied.

[0037] The gate insulating layer 102 may be formed of silicon oxide, silicon nitride, silicon oxynitride, or nitride. An insulator such as silicon oxide, aluminum oxide, or tantalum oxide can be used. A laminated structure made of these insulators may also be applied. The composition of the gas is such that the oxygen content is higher than the nitrogen content, and the oxygen concentration ranges from 5 to 100%. 5-65 atomic %, nitrogen 1-20 atomic %, silicon 25-35 atomic %, hydrogen 0.1- Each element is contained at any concentration within the range of 10 atomic % to make the total 100 atomic %. Silicon nitride oxide is a material whose composition contains more nitrogen than oxygen. The concentration range is 15 to 30 atomic % for oxygen, 20 to 35 atomic % for nitrogen, and Si is in the range of 25 to 35 atomic % and hydrogen is in the range of 15 to 25 atomic %, totaling 100 atomic % It refers to a substance that contains each element at an arbitrary concentration.

[0038] The oxide semiconductor layer 103 may be an In—Ga—Zn—O-based oxide semiconductor, an In—Sn- Zn-O based oxide semiconductors, In-Zn-O based oxide semiconductors, Sn-Zn-O based oxide semiconductors In-Sn-O based oxide semiconductor, Ga-Zn-O based oxide semiconductor, or Zn-O based Oxide semiconductors such as oxide semiconductors can be used. It is also possible to use an oxide semiconductor to which nitrogen (N) or silicon (Si) is added. A laminated structure of these materials can also be applied.

[0039] The pair of conductive layers 104a and 104b may be made of titanium (Ti), copper (Cu), zinc (Zn ), aluminum (Al), etc. can be applied. Furthermore, a laminated structure of these materials can also be applied. do.

[0040] The metal oxide layer 105 is made of the same material as the pair of conductive layers 104a and 104b. However, the metal oxide layer 105 is thicker than the pair of conductive layers 104a and 104b. That is, the metal oxide layer 105 has a high oxygen concentration. The conductive layers 104a and 104b have the same metal element and have a higher oxygen concentration than the conductive layers 104a and 104b.

[0041] The source electrode layer 107a and the drain electrode layer 107b are made of aluminum (Al), Copper (Cu), titanium (Ti), tantalum (Ta), tungsten (W), molybdenum (M o), chromium (Cr), neodymium (Nd), scandium (Sc), It is possible to apply an alloy containing the above-mentioned elements or a nitride containing the above-mentioned elements. Also, a laminated structure of these materials can be applied.

[0042] The pair of oxide semiconductor layers 108a and 108b having reduced oxygen concentrations are formed by using an oxide semiconductor The same material as that of the layer 103 can be used, except that a pair of oxygen-reduced oxides The semiconductor layers 108a and 108b have a lower oxygen concentration than the oxide semiconductor layer 103. The pair of oxide semiconductor layers 108a and 108b with reduced oxygen concentration are The oxide semiconductor layer 103 has the same metal element as the oxide semiconductor layer 3 and has a lower oxygen concentration than the oxide semiconductor layer 103.

[0043] The pair of conductive layers 109a and 109b containing oxygen at a high concentration may be a pair of conductive layers 10 The same materials as those of the metal oxide layer 105 and the metal oxide layer 4a, 104b can be used. The pair of conductive layers 109a and 109b containing oxygen at high concentration are 4b and the metal oxide layer 105. The conductive layers 109a and 109b containing oxygen at a high concentration are b and the metal oxide layer 105, and The oxygen concentration is high and is lower than that of the metal oxide layer 105 .

[0044] The thin film transistor 150 shown in FIG. 1(a) has a source electrode layer 107a and a drain electrode layer 107b. A buffer layer 106 is provided between the electrode layer 107b and the oxide semiconductor layer 103. The metal oxide layer 106 is formed on the central portion of the oxide semiconductor layer 103. The metal oxide layer 105 is formed by absorbing impurities (hydrogen or It functions as a protective layer that prevents the intrusion of water and other substances. An increase in the off-state current or a negative shift in the threshold voltage can be prevented.

[0045] The buffer layer 110 of the thin film transistor 151 shown in FIG. 1(b) increases the off-current, Alternatively, an oxide semiconductor may be formed together with a metal oxide layer 105 that prevents a negative shift in threshold voltage. A pair of oxide semiconductor layers 108a and 108b having reduced oxygen concentration are formed on both ends of the oxide layer 103. The pair of oxide semiconductor layers 108a and 108b with reduced oxygen concentration have the following characteristics. The resistance is lower than that of the source electrode layer 107a and the drain electrode layer 103. The junction between 107b and the oxide semiconductor layer 103 can be an ohmic junction.

[0046] (Embodiment 2) In this embodiment, an example of a method for manufacturing the thin film transistor described in Embodiment 1 will be described. This will be explained with reference to FIGS. 2 and 3.

[0047] In this embodiment, the term "film" refers to a film formed on the entire surface of a substrate. Something that will be processed into a desired shape by a photolithography process, etc., in its pre-processing state And a "layer" is something that is formed from a "film" into a desired shape by a photolithography process or the like. These refer to those processed and formed into a single shape, and those intended to be formed over the entire surface of a substrate. .

[0048] A first conductive film 201 is formed on a substrate 200. The first conductive film 201 is formed by a Sputtering, vacuum evaporation, pulsed laser deposition, ion plating, metal organic vapor phase deposition Next, a thin film deposition method such as a thin film deposition method can be used. A first resist 202 is formed on the substrate 201. The cross-sectional view of the substrate 201 after the above steps is shown in FIG. is equivalent to

[0049] Next, the first conductive film 201 is selectively etched using the first resist 202 as a mask. The gate electrode layer 203 is formed by etching the substrate 200 and the first conductive film The material of 201 (gate electrode layer 203) can be any of the materials listed in Embodiment 1. The first resist 202 is a gate electrode layer. After the process is completed, the cross section of the film is shown in Figure 2(b). .

[0050] Next, a gate insulating layer 204 is formed on the substrate 200 and the gate electrode layer 203. The insulating layer 204 can be formed by a sputtering method, a vacuum evaporation method, a pulsed laser deposition method, an ion plating method, or the like. Thin film deposition methods such as coating, metal organic chemical vapor deposition, and plasma CVD are used. You can be there.

[0051] Next, the oxide semiconductor film 205 is formed. method, vacuum evaporation method, pulsed laser deposition method, ion plating method, metal organic chemical vapor deposition method Thin film deposition methods such as In-Ga-Zn-O oxide semiconductors can be used. When forming the body by sputtering, a substrate made of sintered In2O3, Ga2O3, and ZnO is used. It is preferable to use a get. A rare gas such as argon is used as the sputtering gas. One of the film formation conditions by sputtering is a mixture of In2O3:Ga2O3:ZnO=1:1:1. In this case, a sintered target was used, and the pressure was 0.4 Pa, the direct current (DC) power was 500 W, and the temperature was argon. The gas flow rate is 30 sccm, and the oxygen gas flow rate is 15 sccm. After the semiconductor film 205 is formed, heat treatment is performed at 100°C to 600°C, typically 200°C to 400°C. The heat treatment is preferably carried out to cause rearrangement at the atomic level in the oxide semiconductor. The heat treatment (including photo-annealing) is effective for preventing carrier migration in the oxide semiconductor film 205. This is important because it can release distortions that inhibit movement.

[0052] Next, a second conductive film 206 is formed over the oxide semiconductor film 205. 6 can be formed by sputtering, vacuum evaporation, pulsed laser deposition, ion plating, etc. The second conductive film 206 is made of a thin film deposition method such as metal organic chemical vapor deposition. Titanium (Ti), copper (Cu), zinc (Zn), aluminum (Al), etc. are used. Furthermore, alloys containing the above-mentioned metal elements can also be used. A laminated structure of these materials may also be used. The cross-sectional view at the stage where the process up to this point is completed corresponds to FIG. 2(c). do.

[0053] Next, the oxide semiconductor film 205 and the second conductive film 206 are removed using the second resist 207 as a mask. The oxide semiconductor layer 208 and the conductive layer 209 are removed by selectively etching the film 206. The gate insulating layer 204 and the oxide semiconductor film 205 (the oxide semiconductor layer 208 ) can be the material mentioned in the first embodiment. The second resist 207 is formed by forming the oxide semiconductor layer 208 and the conductive layer 209. The cross section after completing the process up to this point is shown in Figure 2(d).

[0054] Next, a third conductive film 210 is formed over the gate insulating layer 204 and the conductive layer 209. The conductive film 210 can be formed by sputtering, vacuum evaporation, pulsed laser deposition, ion plating, or the like. Thin film deposition methods such as the lattice method and metal organic chemical vapor deposition method can be used. Next, third resists 211a and 211b are formed on the third conductive film 210. The cross-sectional view at the stage where the process up to this point has been completed corresponds to FIG. 3(a).

[0055] Next, the third conductive film 210 is selected using the third resists 211a and 211b as a mask. The source electrode layer 212a and the drain electrode layer 212b are formed by selectively etching the silicon dioxide film. In addition, in the etching step, the source electrode layer 212a and the drain electrode layer 2 The conductive layer 209 in the area (exposed portion) that does not overlap with the source electrode layer 12b is also partially etched. A conductive layer having a recess in a region (exposed portion) that does not overlap with the drain electrode layer 212a and the drain electrode layer 212b The third conductive film 210 (the source electrode layer 212a and the drain electrode layer 213) is formed. The material of the pole layer 212b) can be the same as that of the first embodiment. The cross-sectional view at the stage where the process up to this point is completed corresponds to Figure 3(b). .

[0056] Next, an oxidation process is performed using the third resists 211a and 211b as a mask. The process involves thermal oxidation in an oxidizing atmosphere, plasma oxidation, oxygen ion implantation, etc. In addition, after performing thermal oxidation treatment in an oxidizing atmosphere, plasma oxidation treatment can be performed. It is also possible to combine several of these, for example, by performing the above-mentioned steps. As the atmosphere, a dry oxygen atmosphere, a mixed atmosphere of oxygen and rare gas, or air atmosphere can be used. By the oxidation treatment, the conductive layer 213 provided over the oxide semiconductor layer 208 can be The central portion (exposed portion) of the metal oxide layer 214 is oxidized to form an insulating or semiconducting metal oxide layer 214. In addition, as the metal oxide layer 214 is formed, the pair of conductive layers 215a and 215b are formed as oxide layers. The source electrode layer 212a and the drain electrode layer 212b are formed on both ends of the semiconductor layer 208. The conductive layer 213 in the area (non-exposed portion) overlapping with the source electrode layer 212a and drain electrode layer 212b and third resists 211a and 211b. As a result, a pair of conductive layers 215a and 215b remain. The volume of the area that is oxidized by the treatment increases, i.e., the volume of the metal oxide layer 214 increases. The volume of the central portion of the conductive layer 213 before oxidation is larger than that of the central portion of the conductive layer 213 before oxidation. The surface view corresponds to Figure 3(c). Also, after completing the process up to this point, the The thin film transistor 150 is completed.

[0057] The thin film transistor of this embodiment is not limited to the configuration shown in FIG. 1(a) and FIG. 3(c). Specifically, in FIG. 1(a) and FIG. 3(c), the source The conductive layer 213 in the region (center portion) that does not overlap with the electrode layer 212a and the drain electrode layer 212b The figure shows a thin film transistor in which only the surface is oxidized to form a metal oxide layer 214. The thin film transistor of this embodiment also includes a thin film transistor in which other regions are oxidized. For example, the oxidation process may remove the portions of the substrate that are not covered with the third resists 211a and 211b. The thin film transistor has oxidized sides of the source electrode layer 212a and the drain electrode layer 212b. The source electrode layer 212a and the drain electrode layer 212b are also included in the thin film transistor of this embodiment. When the sides of the inner electrode layer 212b are oxidized, the oxidation is limited to the side surface area. Therefore, the source electrode layer 212a and the drain electrode layer 212b can function as electrodes. Similarly, the source electrode layer 212a and the drain electrode layer 212b can be formed by the oxidation treatment. A thin film transistor in which a part of the conductive layer 213 in the region (non-exposed portion) overlapping with b is internally oxidized. are also included in the thin film transistor of this embodiment.

[0058] In addition, in FIG. 1(a) and FIG. 3(c), the metal oxide layer 2 formed by the oxidation treatment is 14 is thicker than the pair of conductive layers 215a and 215b. However, the thickness of the metal oxide layer 214 is thinner than the thickness of the pair of conductive layers 215a and 215b. The thin film transistor of this embodiment also includes a thin film transistor having a metal oxide. The layer 214 is formed by performing an oxidation process on the conductive layer 213 having the recesses. The recessed portion is formed on the edge where the source electrode layer 212a and the drain electrode layer 212b are formed. That is, the source electrode layer 212a and the drain electrode layer 21 By controlling the conditions of the etching process for forming the metal oxide layer 214, Specifically, the thickness of the source electrode layer 212a and the drain electrode layer 21 By extending the over-etching time when forming 2b, the recess can be made deeper. As a result, the thickness of the metal oxide layer 214 can be reduced by the thickness of the pair of conductive layers 215a and 215b. The thickness can be made thinner than that of 5b.

[0059] In the case of manufacturing the thin film transistor 151 shown in FIG. 1(b), the The heat treatment is carried out at a temperature of 0°C, typically 200°C to 400°C. Oxygen in the conductive layer 208 diffuses into the pair of conductive layers 215a and 215b. When comparing the diffusion into the pair of conductive layers 215a and 215b with the diffusion into the metal oxide layer 214, In this case, the amount of oxygen that diffuses into the pair of conductive layers 215a and 215b is greater. A pair of oxide semiconductor layers 216a and 216b having reduced oxygen concentration are formed on both ends of the semiconductor layer 208. b is formed on the pair of oxide semiconductor layers 216a and 216b with reduced oxygen concentration. Conductive layers 217a and 217b containing oxygen at a high concentration are formed. The cross section after completing the steps up to this stage is shown in FIG. 3(d). Equivalent.

[0060] Here, the heat treatment performed when fabricating the thin film transistor 151 shown in FIG. 1(b) is Although the manufacturing process is shown to be performed after the oxidation treatment, the timing of the heat treatment is determined by the time when the second conductive film 206 The heat treatment can be carried out at any time after the formation. This can also serve as a heat treatment for rearrangement at the atomic level of the oxide semiconductor layer 208.

[0061] In addition, from the viewpoint of the characteristics of the thin film transistors formed, the heat treatment after the oxidation treatment If a heat treatment is performed before the oxidation treatment (before the formation of the metal oxide layer 214), the oxidation The oxide semiconductor layer 208 has an oxide semiconductor layer with a reduced oxygen concentration not only at both upper ends but also over the entire upper portion. This is because an insulating layer is formed, which increases the off-current of the thin film transistor. be.

[0062] In addition, from the viewpoint of the manufacturing process, the above-mentioned oxidation treatment is carried out by using a pair of low oxygen concentrations. The oxide semiconductor layers 216a and 216b and the pair of conductive layers 216a and 216b containing oxygen at a high concentration are It is preferable to perform a thermal oxidation treatment in an oxidizing atmosphere at a temperature at which 17a and 217b are formed. The metal oxide layer 214, the oxide semiconductor layers 216a and 216b with reduced oxygen concentrations, and This is because the conductive layers 217a and 217b containing oxygen at a high concentration can be formed in the same process. One of the conditions for the oxidation treatment and the heat treatment is 350°C in a dry oxygen atmosphere. The thermal oxidation treatment lasts for one hour.

[0063] In addition, from the viewpoint of the reliability of the thin film transistors formed, the thermal oxidation process and the oxidation It is preferable to combine the treatments. and serves as a protective layer that prevents impurities (such as hydrogen or water) from entering the oxide semiconductor layer 208. This is because the functionality of the device can be improved.

[0064] The thin film transistor 150 includes a conductive layer 20 formed in the same process as the oxide semiconductor layer 208. 9 (conductive layer 213) to prevent an increase in off-current or a negative shift in threshold voltage Since the metal oxide layer 214 having the function of Similarly, the thin film transistor 151 can be formed by forming an oxide semiconductor layer 20 The conductive layer 209 (conductive layer 213) formed in the same process as in Example 8 is used to increase the off-state current, or A metal oxide layer 214 having the function of preventing a negative shift of the threshold voltage is formed. The oxide semiconductor layer 208, the source electrode layer 212a, and the drain electrode layer 212b are connected to each other. A pair of oxide semiconductor layers 216a and 216b having a reduced oxygen concentration and functioning as a hysteretic junction 16b is formed by oxygen diffusing into the pair of conductive layers 215a, 215b. Therefore, high-performance thin film transistors can be formed efficiently.

[0065] (Embodiment 3) In this embodiment, one of the semiconductor devices using the thin film transistor described in the first embodiment is Specifically, the thin film transistor is set in the pixel portion of the active matrix substrate. A liquid crystal display device using the thin film transistor is shown in FIGS. The liquid crystal display device will now be described.

[0066] In the semiconductor device, the source and drain of the thin film transistor are It is difficult to identify which is the source and which is the drain because they are interchanged depending on the Therefore, in the following embodiments, one of the source electrode layer and the drain electrode layer is The other of the first electrode layer, the source electrode layer, and the drain electrode layer is referred to as a second electrode layer to distinguish it from the other. Let's say.

[0067] 4 is a top view showing one pixel of the active matrix substrate. A pixel of the display device is made up of three sub-pixels. A pixel electrode 301 is provided to apply a voltage to the transistor 300 and the liquid crystal layer. The thin film transistor shown in can be applied to the thin film transistor 300 in FIG. The pixel section is provided with a plurality of the above-described pixels. A source line 303 and a plurality of capacitance lines 304 are provided.

[0068] 5 is a cross-sectional view corresponding to the line AB in FIG. 4. 50 is the thin film transistor shown in FIG. 1(a). That is, the thin film transistor 450 The gate electrode layer 401 is provided on the substrate 400, and the gate electrode layer 402 is provided on the gate electrode layer 401. a gate insulating layer 402 formed thereon; an oxide semiconductor layer 403 provided over the gate insulating layer 402; A pair of conductive layers 404a and 404b and a metal oxide semiconductor layer 406 are provided over the oxide semiconductor layer 403. a buffer layer 406 having a layer 405 and a first electrode layer 407 disposed on the conductive layer 404a; a) and a second electrode layer 407b provided on the conductive layer 404b. is.

[0069] Applicable materials and fabrication methods for the substrate 400 to the first electrode layer 407a and the second electrode layer 407b The material described in Embodiment 1 and the manufacturing method described in Embodiment 2 are used. Therefore, the above explanation is used here.

[0070] The subpixel also includes a capacitor 451. The capacitor 451 is formed by a thin film transistor 450. The gate electrode layer 401 is made of the same material as the capacitor wiring 408, the gate insulating layer 402, and the sub-pixel. and a second electrode layer 407b of the thin film transistor 450 extending along the substrate.

[0071] An interlayer insulating layer 409 is provided over the thin film transistor 450 and the capacitor 451 . In the thin film transistor 450 shown in FIG. 5, impurities (hydrogen or water) are added to the oxide semiconductor layer 403. The metal oxide layer 405 is provided to prevent the penetration of foreign matters such as the metal oxide layer 405. For example, the interlayer insulating layer 409 may be made of polyimide. Using plasma CVD or sputtering, silicon oxide layer, silicon oxynitride layer, silicon nitride layer A silicon layer, a silicon nitride oxide layer, or the like can be formed. organic compounds such as amide, polyvinylphenol, benzocyclobutene, acrylic or epoxy Materials, siloxane materials such as siloxane resins, or oxazole resins, etc., are used to form spin The siloxane material can be formed by a coating method such as a Si- It corresponds to a material containing an O-Si bond. Siloxane is a compound of silicon (Si) and oxygen (O). The skeleton is made up of bonds. Substituents include organic groups (e.g., alkyl groups, aromatic hydrocarbons, etc.). The organic group may have a fluoro group. In the contact hole 410 provided in the interlayer insulating layer 409, the thin film transistor 450 The second electrode layer 407 b is electrically connected to the pixel electrode 411 .

[0072] 6 is an equivalent circuit diagram corresponding to the subpixel of FIG. The first electrode is electrically connected to the gate line 501, and the second electrode is electrically connected to the source line 502. One electrode of the capacitor 503 is electrically connected to the second electrode of the thin film transistor 500. The other electrode is electrically connected to the capacitor wiring 504. The liquid crystal layer 505 to which the voltage is applied is connected to the second electrode of the thin film transistor 500 and one of the capacitor elements 503. The electrode is electrically connected to the other electrode.

[0073] A liquid crystal display device is made up of an active matrix substrate and a counter substrate on the surface of which a counter electrode is provided. The liquid crystal layer is sandwiched between the active matrix and the liquid crystal molecules. The alignment is controlled by the voltage applied between the pixel electrode on the pixel substrate and the counter electrode on the counter substrate. The liquid crystal display device receives light from the backlight by aligning the liquid crystal molecules in the liquid crystal layer. In a liquid crystal display device, an image is displayed by transmitting or blocking light. The thin-film transistors in the pixel section of the active matrix substrate control the voltage applied to the liquid crystal layer. It is a switching element that controls

[0074] In the liquid crystal display device of this embodiment, a metal oxide layer 405 is provided over an oxide semiconductor layer 403. The thin film transistor 450 is a thin film transistor in the pixel portion of the active matrix substrate. The metal oxide layer 405 is used as an impurity (hydrogen or It functions as a protective layer that prevents the penetration of substances such as water. 409 materials and manufacturing methods can be selected, resulting in high quality and high reliability It is possible to provide a liquid crystal display device with high optical properties. The liquid crystal display device using the thin film transistor shown in Fig. 1(b) is The same effect can be achieved when a resistor is applied.

[0075] (Fourth embodiment) In this embodiment, one of the semiconductor devices using the thin film transistor described in the first embodiment is Specifically, the thin film transistor is set in the pixel portion of the active matrix substrate. A light-emitting display device using a thin film transistor that can be used is shown in FIGS. The light-emitting display device of this embodiment will be described. Here, a light-emitting element using electroluminescence is used as a display element. The light-emitting element that uses electroluminescence is either an organic compound or Generally, the former is an organic EL element, and the latter is an inorganic EL element. It is called the L element.

[0076] In an organic EL element, when a voltage is applied to the light-emitting element, electrons and positive electrodes are released from a pair of electrodes. The holes are then injected into a layer containing a light-emitting organic compound, allowing a current to flow. The recombination of carriers (electrons and holes) causes light-emitting organic compounds to form excited states. The excited state is formed, and light is emitted when the excited state returns to the ground state. Such a light-emitting element is called a current-excited light-emitting element.

[0077] Inorganic EL elements are classified into dispersion-type inorganic EL elements and thin-film-type inorganic EL elements depending on the element structure. Dispersion-type inorganic EL elements have a light-emitting layer in which particles of light-emitting material are dispersed in a binder. The emission mechanism is a donor- The thin-film inorganic EL element is an acceptor recombination type luminescence element. The luminescent layer is sandwiched between dielectric layers. The structure is sandwiched between electrodes, and the light emission mechanism is the inner shell electron transition of the metal ion. This is a localized light emission that utilizes organic EL elements. do.

[0078] 7 is a top view showing one pixel of the active matrix substrate. A pixel of the display device is made up of three sub-pixels. The pixel electrode 602 for applying a voltage to the light-emitting element is provided (for convenience). Therefore, a part of the pixel electrode 602 is not shown. This can be applied to the thin film transistors 600 and 601 in FIG. In addition, a plurality of gate wirings 603, a plurality of source wirings 604, A plurality of power supply lines 605 are provided. A high power supply potential VDD is set to the power supply lines 605. It is being done.

[0079] 8 is a cross-sectional view taken along lines CD and EF in FIG. , 751 are the thin film transistors shown in FIG. 1(a). 50 and 751 are gate electrode layers 701 and 702 provided on a substrate 700. a gate insulating layer 702 provided thereon and an oxide semiconductor layer provided thereon; the oxide semiconductor layer 703, the conductive layers 704a and 704b, and the metal A buffer layer 706 having an oxide layer 705 and a first electrode layer provided on the conductive layer 704a. 707a and a second electrode layer 707b provided on the conductive layer 704b. It's Jista.

[0080] Applicable materials and fabrication methods for the substrate 700 to the first electrode layer 707a and the second electrode layer 707b The material described in Embodiment 1 and the manufacturing method described in Embodiment 2 are used. Therefore, the above explanation is used here.

[0081] The subpixel also includes a capacitor 752. The capacitor 752 is formed by a thin film transistor 750. , 751, the gate electrode layer 701 and the capacitance wiring 708 made of the same material, and the gate insulating layer 702 and a first electrode layer 707a of a thin film transistor 751 extending to the sub-pixel. can be.

[0082] An interlayer insulating layer 709 is provided over the thin film transistors 750 and 751 and the capacitor element 752. In the thin film transistors 750 and 751 shown in FIG. The metal oxide layer 705 that prevents impurities (such as hydrogen or water) from penetrating is provided. Various materials and manufacturing methods can be applied to the interlayer insulating layer 709. For example, 709, a silicon oxide layer, a silicon oxynitride layer, etc. are formed by using plasma CVD or sputtering. A silicon layer, a silicon nitride layer, a silicon oxynitride layer, or the like can be formed. Polyimide, polyamide, polyvinylphenol, benzocyclobutene, acrylic or Organic materials such as epoxy, siloxane materials such as siloxane resin, or oxazole resin, etc. The layer can be formed by a coating method such as spin coating using siloxane. The material corresponds to a material containing Si-O-Si bonds. Siloxane is a compound containing silicon (Si) The skeleton is made up of bonds between the alkyl group and oxygen (O). The organic group may have a fluoro group. The interlayer insulating layer 709 may also have a plurality of contact holes 710a, 710b, 710c, 710d, 710e, 710f, 710g, 710h, 710i, 710j, 710m, 710m. The second electrode layer 707b of the thin film transistor 751 is provided with a contact hole 10c. The electrode 710c is electrically connected to the pixel electrode 711.

[0083] 9 is an equivalent circuit diagram corresponding to the subpixel of FIG. 7. The gate of the thin film transistor 800 The first electrode is electrically connected to the gate wiring 801, and the second electrode is electrically connected to the source wiring 802. One electrode of the capacitor 803 is electrically connected to the second electrode of the thin film transistor 800. The other electrode is electrically connected to a power supply line 804. The gate electrode is electrically connected to the second electrode of the thin film transistor 800, and the first electrode is connected to the power supply line. The pixel electrode 804 is connected to the other electrode of the capacitor element 803. A voltage is applied through the pixel electrode. The organic EL element 806 is electrically connected to the second electrode of the thin film transistor 805 .

[0084] The light-emitting display device has an organic EL element provided on a pixel electrode of an active matrix substrate. and a common electrode provided on the organic EL element. The organic EL element is connected to the pixel electrode via a thin film transistor. The potential difference between the high power supply potential VDD applied to the common electrode and the low power supply potential VSS applied to the common electrode is When voltage is applied, a current flows and light is emitted. The thin-film transistors in the pixel area of ​​the substrate are switches that control the current flowing through the organic EL elements. It is a gate element.

[0085] In the light-emitting display device of this embodiment, a metal oxide layer 705 is provided over an oxide semiconductor layer 703. The thin film transistors 750 and 751 are connected to the thin film transistors in the pixel portion of the active matrix substrate. The metal oxide layer 705 is used as a transistor. It functions as a protective layer that prevents the penetration of gases such as hydrogen or water. It is possible to select the material and manufacturing method of the interlayer insulating layer 709. As a result, high quality or This makes it possible to provide a highly reliable light-emitting display device. The light-emitting display device using the thin film transistor shown in FIG. The same effect can be achieved when a film transistor is used.

[0086] (Embodiment 5) In this embodiment, one of the semiconductor devices using the thin film transistor described in the first embodiment is Specifically, the thin film transistor is provided on an active matrix substrate. FIG. 10 shows electronic paper applied to thin film transistors. This article explains electronic paper.

[0087] FIG. 10 is a cross-sectional view of an active matrix electronic paper. The thin film transistor 950 provided on the active matrix substrate 900 is shown in FIG. That is, the thin film transistor 950 is a thin film transistor formed on the first substrate 900. a gate electrode layer 901 provided thereon; and a gate insulating layer provided thereon. 902, an oxide semiconductor layer 903 provided over the gate insulating layer 902, and an oxide semiconductor layer A pair of conductive layers 904a and 904b and a metal oxide layer 905 are provided on a substrate 903. a buffer layer 906 formed on the conductive layer 904a; a first electrode layer 907a formed on the conductive layer 904a; and a second electrode layer 907b provided on the first electrode layer 904b.

[0088] Applicable materials and fabrication methods for the substrate 900 to the first electrode layer 907a and the second electrode layer 907b The material described in Embodiment 1 and the manufacturing method described in Embodiment 2 are used. Therefore, the above explanation is used here.

[0089] An interlayer insulating layer 908 is provided on the thin film transistor 950. The transistor 950 has a structure for preventing impurities (such as hydrogen or water) from entering the oxide semiconductor layer 903. Since the metal oxide layer 905 is provided, various materials and processes can be used as the interlayer insulating layer 908. For example, the interlayer insulating layer 908 can be formed by a plasma CVD method or A silicon oxide layer, a silicon oxynitride layer, a silicon nitride layer, or a nitride layer is formed by a sputtering method. A silicon oxide layer or the like can be formed. Also, polyimide, polyamide, polyvinyl Phenol, benzocyclobutene, organic materials such as acrylic or epoxy, siloxane Siloxane resin or oxazole resin is used for coating by spin coating method. It can be formed by a method using a siloxane material containing Si-O-Si bonds. Siloxane has a skeleton structure formed by the bond between silicon (Si) and oxygen (O). The substituents include organic groups (e.g., alkyl groups, aromatic hydrocarbons) and fluoro groups. The organic group may have a fluoro group. A contact hole 909 is provided in the second electrode layer 907 of the thin film transistor 950. b is electrically connected to the pixel electrode 910 through a contact hole 909 .

[0090] Between the pixel electrode 910 and the common electrode 912 provided on the second substrate 911, a black area is formed. 913a and white area 913b, and a cavity 914 filled with liquid therearound. The twist ball 915 is provided with a resin or the like around it. The filler 916 is filled with the filler material.

[0091] The electronic paper of this embodiment uses a twisting ball display method. The par has twist balls painted in black and white between the pixel electrode and the common electrode. The isotropic ball is a pixel that changes in response to a voltage applied between the pixel electrode on the first substrate and the common electrode on the second substrate. Therefore, the display is controlled by controlling the orientation. The thin film transistors on the active matrix substrate control the voltage applied to the twist balls. It is a switching element.

[0092] In the light-emitting display device of this embodiment, a metal oxide layer 905 is provided over an oxide semiconductor layer 903. The thin film transistor 950 is used as a thin film transistor of an active matrix substrate. The metal oxide layer 905 prevents impurities (such as hydrogen or water) from entering the oxide semiconductor layer 903. Therefore, depending on the purpose, the insulating interlayer 908 functions as a protective layer that prevents the penetration of It is possible to select materials and fabrication methods, resulting in high quality and high reliability electronics. It is possible to provide paper. We have shown electronic paper using thin film transistors, as shown in Figure 1(b). The same effect is achieved when applied. [Example]

[0093] Here, we will examine the changes in the electronic state of titanium and titanium oxide due to differences in oxygen content, Changes in electronic state due to oxygen deficiency in semiconductor layers, titanium layers and oxide semiconductors under heat treatment Behavior of oxygen near the interface of the titanium oxide layer and the titanium oxide layer under heat treatment The calculation results for the behavior of oxygen near the junction interface of the semiconductor layer are shown below. The thin film transistor of the first embodiment in which titanium is used as the constituent material of the silicon layer will be examined.

[0094] First, we will examine the changes in the electronic state of titanium and titanium oxide due to differences in oxygen content. Here, the energy density of states of the crystal structures of titanium and several titanium oxides is calculated using density functionals. Plane wave based on Density Functional Theory (DFT) -Results obtained by structural optimization using first-principles calculations with pseudopotential methods Specifically, Ti, TiO (NaCl type), Ti2O3 (Al2O3 type), TiO 2 (Anatase type), TiO2 (Rutile type), and TiO2 (Brookit The density of states diagram after optimizing the structure of the e-type is shown. TEP was used as the functional, and GGA-PBE was used as the exchange-correlation functional.

[0095] Figure 11(a), (b), and (c) show the results for Ti, TiO (NaCl type), and Ti2O3, respectively. Figures 11(a), (b), and (c) show the density of states of the band gap (Al2O3 type). In other words, Ti, TiO (NaCl type), and Ti2O3 (Al2O3 type) are conductive. It is an electric body.

[0096] Figure 12(a), (b), and (c) show the results of TiO2 (Anatase type), TiO2 Fig. 12(a) shows the density of states of TiO2 (Rutile type) and TiO2 (Brookite type). The Fermi levels (0 eV) of (b), (c) are at the top of the valence band and There are three types of TiO2: TiO2 (Anatase type), TiO2 (Rutile type), and T iO2 (Brookite type) is an insulator or semiconductor.

[0097] From Figures 11 and 12, it can be seen that titanium is a conductor even if it contains less than a certain amount of oxygen. It can be seen that when the material contains more than this amount of oxygen, it becomes an insulator or a semiconductor.

[0098] Next, we will examine the change in the electronic state due to oxygen vacancies in the oxide semiconductor layer. The semiconductor layer is made of an In-Ga-Zn-O oxide semiconductor material (In:Ga:Zn:O = Calculations are performed using the ratio (1:1:1:4).

[0099] First, Classical Molecular Dynamics ) calculations of In-Ga-Zn-O oxide semiconductors using the melt-quench method. The amorphous structure created here has a total of 84 atoms and a density of 5.9g / cm 3 The interatomic potential is between the metal and oxygen, and between the oxygen and For oxygen, a Born-Mayer-Huggins potential is used, and for metal-gold, Between genera, a Lennard-Jones type potential is used, and the NVT ensemble The calculation was performed using Materials Explorer. Used.

[0100] Then, the structure obtained by the above calculation is subjected to density functional theory (DFT). We used a plane wave pseudopotential method based on Functional Theory (DFT). First Principle Molecular Dynamics Annealing by first-principles MD (dynamics: hereafter referred to as first-principles MD) was performed at room temperature (298 K). Afterwards, the structure was optimized and the density of states was calculated. First-principles MD calculations and structural optimization were also performed for the structure (oxygen deficiency structure) to calculate the density of states. The calculation program was CASTEP, and the exchange-correlation functional was GGA. -PBE was used, and first-principles MD was performed on the NVT ensemble.

[0101] Figures 13(a) and (b) show the In-Ga-Zn-O oxide semiconductors obtained by the above calculations. Fig. 13(a) is a density of states diagram of a structure without oxygen vacancies, and Fig. 1 3(b) is a density of states diagram of the oxygen deficiency structure. In FIG. 13(a), the Fermi level ( 0 eV) is at the upper end of the valence band and has a band gap, whereas in Fig. 13(b), In this case, the Fermi level (0 eV) is located within the conduction band. It can be seen that the structure has lower resistance compared to a structure without oxygen vacancies.

[0102] Next, the behavior of oxygen near the junction interface between the titanium layer and the oxide semiconductor layer during heat treatment was investigated. Here, we investigate the behavior of the In-Ga-Zn Titanium is stacked on the amorphous structure of -O-based oxide semiconductor, and the structure is optimized. After that, we performed first-principles MD calculations using the NVT ensemble. CASTEP was used as the exchange-correlation functional, and GGA-PBE was used as the exchange-correlation functional. The temperature was set to 50°C (623K).

[0103] Figure 14 shows the structures before and after first-principles MD. Figure 14(a) shows the structure before first-principles MD. Figure 14(b) shows the structure after first-principles MD. 14. The density of titanium and oxygen in the c-axis direction is shown in FIG. 15. The density distribution is calculated by assigning a distribution type density and adding up all atoms. The horizontal axis of Fig. 5 represents the atomic density, and the vertical axis represents the c-axis. Density of titanium before MD (Ti_before), density of titanium after first-principles MD (Ti_ after), oxygen density before first-principles MD (O_before), oxygen density after first-principles MD From Figure 15, O_after represents the density of the original data (O_after). The oxygen concentration in titanium is higher in the positive direction of the c-axis than in the first-principles MD. In other words, the oxide semi-conductor is increased by the heat treatment at 350℃ (623K). It can be seen that oxygen in the conductor layer diffuses into the titanium layer.

[0104] Next, titanium oxide (here, TiO2 (Rutile type)) in the heat treatment The behavior of oxygen near the junction interface between the silicon dioxide layer and the oxide semiconductor layer will be examined. is the amorphous In-Ga-Zn-O oxide semiconductor obtained by the first-principles calculations mentioned above. TiO2 (Rutile type) was layered on the structure, and the structure was optimized. Afterwards, first-principles MD calculations were performed using the NVT ensemble. The TEP was used as the exchange-correlation functional, and the GGA-PBE was used as the exchange-correlation functional. The temperature condition was 700°C. (973K).

[0105] Figure 16 shows the structures before and after first-principles MD. Figure 16(a) shows the structure before first-principles MD. Figure 16(b) shows the structure after first-principles MD. 16. The density of titanium and oxygen in the c-axis direction is shown in FIG. 17. The density distribution is calculated by assigning a distribution type density and adding up all atoms. The horizontal axis of Fig. 7 represents the atomic density, and the vertical axis represents the c-axis. Density of titanium before MD (Ti_before), density of titanium after first-principles MD (Ti_ after), oxygen density before first-principles MD (O_before), oxygen density after first-principles MD Figure 17 shows the density of the original (O_after) as seen in Figure 15. There is no significant difference between O_after and O_before. Even after heat treatment, the diffusion of oxygen between the oxide semiconductor layer and the TiO2 (rutile type) layer It can be seen that the diffusion between the oxide semiconductor layer and the titanium layer at 350°C is not as active as that between the oxide semiconductor layer and the titanium layer at 350°C.

[0106] The results of the calculations performed in this example are summarized below.

[0107] As can be seen from Figures 11 and 12, the electronic states of the titanium oxides are different, and the oxygen concentration It was found that as the temperature increased, the material became either an insulator or a semiconductor. TiO2 (Anatase type), TiO3 (Al2O3 type) are conductors, iO2 (Rutile type) and TiO2 (Brookite type) are insulators or semiconductors In other words, titanium oxide becomes an insulator or a semiconductor when the oxygen content is high. It was found that the electronic state changes depending on the oxygen ratio.

[0108] As can be seen from Figure 13, the In-Ga-Zn-O oxide semiconductor has an oxygen deficiency structure. It was found that the electron state changes and the resistance decreases. The amorphous structure has (In:Ga:Zn:O=1:1:1:4) and oxygen atoms from the structure. In other words, the electron state of the structure with one oxygen atom removed is compared. at.% (oxygen atoms 48 / total atoms 84) and the oxygen concentration is about 56.6at.% ( The number of oxygen atoms is 47, and the total number of atoms is 83. Compared to the titanium mentioned above, the -O-based oxide semiconductor has a different effect on the electronic state when the oxygen concentration changes. It can be said that this material has a large impact.

[0109] 14 and 15, the stacking of the titanium layer and the In-Ga-Zn-O-based oxide semiconductor layer On the other hand, when heat treatment is performed at 350°C, oxygen in the In-Ga-Zn-O based oxide semiconductor layer is converted to thiazolinone. In other words, the heat treatment diffuses the titanium layer more rapidly than the titanium layer before the heat treatment. The titanium layer contains oxygen at a higher concentration than the oxide semiconductor layer before the heat treatment. It was found that a thin oxide semiconductor layer was formed. -Considering the influence of changes in oxygen concentration in Zn-O-based oxide semiconductors on their respective electronic states, As a result, the titanium layer containing a high concentration of oxygen does not increase the resistance as much as the titanium layer. On the other hand, the oxide semiconductor layer with a reduced oxygen concentration has a lower resistance than the oxide semiconductor layer. It is thought that it will fall.

[0110] 16 and 17, the TiO2 (rutile type) layer and the In-Ga-Zn-O system oxide Even if the laminated layer of the oxide semiconductor is heat-treated at a high temperature of 700°C, the oxide It was found that diffusion is less likely to occur in the layered structure than in the layered structure of the nitride semiconductor layer and the titanium layer. In other words, even after heat treatment, the oxygen concentration is lower than that of the stack of the oxide semiconductor layer and the titanium layer. It was found that a thin oxide semiconductor layer was hardly formed.

[0111] Next, the case where titanium is applied to the buffer layer of the thin film transistor of the first embodiment will be described. The titanium layer is oxidized to form TiO2 (Anata), which is an insulator or semiconductor. titanium dioxide, such as TiO2 (rutile type), TiO2 (brookite type) By forming a metal oxide, it can be used as a metal oxide layer of the buffer layer. In addition, by performing the heat treatment at 350° C., oxygen from the oxide semiconductor layer is oxidized to the titanium layer. The titanium layer containing high oxygen concentration and the oxide semiconductor layer containing low oxygen concentration are formed. Therefore, the resistance of the oxide semiconductor layer is effectively reduced, and the source The electrode layer and the drain electrode layer can be ohmic junctions with the oxide semiconductor layer. In addition, at the interface between the oxide semiconductor layer and the metal oxide layer, the oxide semiconductor layer and the metal oxide layer are electrically conductive. Compared to the interface of the layer, oxygen diffusion is difficult. Therefore, at the interface, The oxide semiconductor layer with a reduced oxygen concentration is difficult to form, and the off-current of the thin film transistor increases. This can suppress the increase in the temperature.

[0112] From the above, titanium is a material suitable for use in the buffer layer of the thin film transistor of the first embodiment. It was found to be a preferable material. [Explanation of symbols]

[0113] 100 boards 101 gate electrode layer 102 Gate insulating layer 103 Oxide semiconductor layer 104a Conductive layer 104b Conductive layer 105 Metal oxide layer 106 Buffer Layer 107a Source electrode layer 107b Drain electrode layer 108a Oxide semiconductor layer with reduced oxygen concentration 108b Oxide semiconductor layer with reduced oxygen concentration 109a Conductive layer containing high concentration of oxygen 109b Conductive layer containing high concentration of oxygen 110 Buffer layer 150 Thin-Film Transistor 151 Thin-film transistor 200 boards 201 First conductive film 202 First Resist 203 Gate electrode layer 204 Gate insulating layer 205 Oxide semiconductor film 206 Second conductive film 207 Second Resist 208 Oxide semiconductor layer 209 Conductive Layer 210 Third conductive film 211a Third Resist 211b Third Resist 212a Source electrode layer 212b Drain electrode layer 213 Conductive Layer 214 Metal oxide layer 215a conductive layer 215b Conductive layer 216a Oxide semiconductor layer with reduced oxygen concentration 216b Oxide semiconductor layer with reduced oxygen concentration 217a Conductive layer containing high concentration of oxygen 217b Conductive layer containing high concentration of oxygen 300 Thin Film Transistor 301 Pixel electrode 302 Gate wiring 303 Source wiring 304 Capacitance wiring 400 boards 401 Gate electrode layer 402 Gate insulating layer 403 Oxide semiconductor layer 404a Conductive layer 404b conductive layer 405 Metal oxide layer 406 Buffer Layer 407a 1st electrode layer 407b 2nd electrode layer 408 Capacitance wiring 409 Interlayer insulation layer 410 Contact Hole 411 Pixel electrode 450 Thin Film Transistor 451 Capacitor 500 Thin Film Transistors 501 Gate wiring 502 Source wiring 503 Capacitor 504 Capacitance wiring 505 Liquid crystal layer 600 Thin Film Transistors 601 Thin-film transistor 602 pixel electrode 603 Gate wiring 604 Source wiring 605 Power line 700 boards 701 Gate electrode layer 702 Gate insulating layer 703 Oxide semiconductor layer 704a conductive layer 704b conductive layer 705 Metal Oxide Layer 706 Buffer Layer 707a 1st electrode layer 707b Second electrode layer 708 Capacitance wiring 709 Interlayer insulation layer 710a Contact hole 710b Contact hole 710c Contact Hole 711 Pixel electrode 750 Thin Film Transistors 751 Thin-film transistor 752 Capacitor 800 thin film transistors 801 Gate wiring 802 source wiring 803 Capacitor 804 Power line 805 Thin Film Transistor 806 Organic EL element 900 boards 901 Gate electrode layer 902 Gate insulating layer 903 Oxide semiconductor layer 904a conductive layer 904b Conductive layer 905 Metal oxide layer 906 Buffer Layer 907a 1st electrode layer 907b 2nd electrode layer 908 Interlayer insulation layer 909 Contact Hole 910 Pixel electrode 911 board 912 Common electrode 913a black area 913b White area 914 Cavity 915 Twist Ball 916 Filling material 950 Thin Film Transistor

Claims

1. a pixel including a first transistor, a second transistor, and an organic EL element; one of a source and a drain of the first transistor is electrically connected to a source wiring; the other of the source and the drain of the first transistor is electrically connected to the gate of the second transistor; one of the source and the drain of the second transistor is electrically connected to a power supply line; the other of the source and the drain of the second transistor is electrically connected to a pixel electrode of the organic EL element; a first oxide semiconductor layer including a channel formation region of the first transistor; a second oxide semiconductor layer including a channel formation region of the second transistor; a first conductive layer that overlaps with a channel formation region of the second transistor and functions as a gate of the second transistor; a second conductive layer having a function of connecting the other of the source and the drain of the first transistor and the gate of the second transistor and having a region in contact with the first conductive layer; a third conductive layer having a function as the source wiring; a fourth conductive layer having a function as the power supply line; a first insulating layer having a region in contact with an upper surface of the third conductive layer and a region in contact with an upper surface of the fourth conductive layer; the third conductive layer and the fourth conductive layer have the same material; the second conductive layer and the pixel electrode have the same material; an upper surface of the second conductive layer is not in contact with the first insulating layer; The pixel electrode overlaps with a channel formation region of the first transistor.

2. a pixel including a first transistor, a second transistor, and an organic EL element; one of a source and a drain of the first transistor is electrically connected to a source wiring; the other of the source and the drain of the first transistor is electrically connected to the gate of the second transistor; one of the source and the drain of the second transistor is electrically connected to a power supply line; the other of the source and the drain of the second transistor is electrically connected to a pixel electrode of the organic EL element; a first oxide semiconductor layer including a channel formation region of the first transistor; a second oxide semiconductor layer including a channel formation region of the second transistor; a first conductive layer that overlaps with a channel formation region of the second transistor and functions as a gate of the second transistor; a second conductive layer having a function of connecting the other of the source and the drain of the first transistor and the gate of the second transistor and having a region in contact with the first conductive layer; a third conductive layer having a function as the source wiring; a fourth conductive layer having a function as the power supply line; a first insulating layer having a region in contact with an upper surface of the third conductive layer and a region in contact with an upper surface of the fourth conductive layer; the third conductive layer and the fourth conductive layer have the same material; the second conductive layer and the pixel electrode have the same material; an upper surface of the second conductive layer is not in contact with the first insulating layer; the pixel electrode overlaps with a channel formation region of the first transistor; the third conductive layer has a region extending in a first direction; the fourth conductive layer has a region extending in the first direction, The second conductive layer has a region extending in a second direction intersecting the first direction.

3. a pixel including a first transistor, a second transistor, and an organic EL element; one of a source and a drain of the first transistor is electrically connected to a source wiring; the other of the source and the drain of the first transistor is electrically connected to the gate of the second transistor; one of the source and the drain of the second transistor is electrically connected to a power supply line; the other of the source and the drain of the second transistor is electrically connected to a pixel electrode of the organic EL element; a first oxide semiconductor layer including a channel formation region of the first transistor; a second oxide semiconductor layer including a channel formation region of the second transistor; a first conductive layer that overlaps with a channel formation region of the second transistor and functions as a gate of the second transistor; a second conductive layer having a function of connecting the other of the source and the drain of the first transistor and the gate of the second transistor and having a region in contact with the first conductive layer; a third conductive layer having a function as the source wiring; a fourth conductive layer having a function as the power supply line; a first insulating layer having a region in contact with an upper surface of the third conductive layer and a region in contact with an upper surface of the fourth conductive layer; the third conductive layer and the fourth conductive layer have the same material; the second conductive layer and the pixel electrode have the same material; an upper surface of the second conductive layer is not in contact with the first insulating layer; the pixel electrode overlaps with a channel formation region of the first transistor; the third conductive layer has a region extending in a first direction; the fourth conductive layer has a region extending in the first direction, the second conductive layer has a region extending in a second direction intersecting the first direction; The display device, wherein the first transistor has a region in which a channel length direction is the second direction.

4. In any one of claims 1 to 3, The pixel has a capacitance element, The display device, wherein the first conductive layer functions as one electrode of the capacitor.

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