WO2015079362A1 - Semiconductor device - Google Patents

Semiconductor device Download PDF

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Publication number
WO2015079362A1
WO2015079362A1 PCT/IB2014/066150 IB2014066150W WO2015079362A1 WO 2015079362 A1 WO2015079362 A1 WO 2015079362A1 IB 2014066150 W IB2014066150 W IB 2014066150W WO 2015079362 A1 WO2015079362 A1 WO 2015079362A1
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WO
WIPO (PCT)
Prior art keywords
film
oxide semiconductor
oxide
conductive film
semiconductor film
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/IB2014/066150
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English (en)
French (fr)
Inventor
Shunpei Yamazaki
Junichi Koezuka
Yukinori Shima
Masami Jintyou
Takashi Hamochi
Satoshi Higano
Yasuharu Hosaka
Toshimitsu Obonai
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Semiconductor Energy Laboratory Co Ltd
Original Assignee
Semiconductor Energy Laboratory Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Semiconductor Energy Laboratory Co Ltd filed Critical Semiconductor Energy Laboratory Co Ltd
Priority to KR1020167017512A priority Critical patent/KR102306201B1/ko
Priority to CN201480064849.3A priority patent/CN105793994B/zh
Priority to DE112014005438.0T priority patent/DE112014005438T5/de
Publication of WO2015079362A1 publication Critical patent/WO2015079362A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D30/00—Field-effect transistors [FET]
    • H10D30/60—Insulated-gate field-effect transistors [IGFET]
    • H10D30/67—Thin-film transistors [TFT]
    • H10D30/674—Thin-film transistors [TFT] characterised by the active materials
    • H10D30/6755—Oxide semiconductors, e.g. zinc oxide, copper aluminium oxide or cadmium stannate
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D1/00—Resistors, capacitors or inductors
    • H10D1/40—Resistors
    • H10D1/47—Resistors having no potential barriers
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D1/00—Resistors, capacitors or inductors
    • H10D1/40—Resistors
    • H10D1/47—Resistors having no potential barriers
    • H10D1/474—Resistors having no potential barriers comprising refractory metals, transition metals, noble metals, metal compounds or metal alloys, e.g. silicides
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D1/00—Resistors, capacitors or inductors
    • H10D1/60—Capacitors
    • H10D1/68—Capacitors having no potential barriers
    • H10D1/692—Electrodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D30/00—Field-effect transistors [FET]
    • H10D30/60—Insulated-gate field-effect transistors [IGFET]
    • H10D30/67—Thin-film transistors [TFT]
    • H10D30/674—Thin-film transistors [TFT] characterised by the active materials
    • H10D30/6755—Oxide semiconductors, e.g. zinc oxide, copper aluminium oxide or cadmium stannate
    • H10D30/6756—Amorphous oxide semiconductors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D64/00—Electrodes of devices having potential barriers
    • H10D64/60—Electrodes characterised by their materials
    • H10D64/62—Electrodes ohmically coupled to a semiconductor
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D86/00—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates
    • H10D86/40—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates characterised by multiple TFTs
    • H10D86/441—Interconnections, e.g. scanning lines
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D86/00—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates
    • H10D86/40—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates characterised by multiple TFTs
    • H10D86/481—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates characterised by multiple TFTs integrated with passive devices, e.g. auxiliary capacitors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D86/00—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates
    • H10D86/40—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates characterised by multiple TFTs
    • H10D86/60—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates characterised by multiple TFTs wherein the TFTs are in active matrices

Definitions

  • One embodiment of the present invention relates to a semiconductor device and a display device each including an oxide semiconductor.
  • one embodiment of the present invention is not limited to the above technical field.
  • the technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method.
  • one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter.
  • examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a light-emitting device, a power storage device, a storage device, a method for driving any of them, and a method for manufacturing any of them.
  • an aluminum film has been widely used as a material used for the wiring, the signal line, or the like; moreover, research and development of using a copper (Cu) film as a material is extensively conducted to further reduce resistance.
  • a copper (Cu) film is disadvantageous in that adhesion thereof to a base film is poor and that characteristics of a transistor easily deteriorate due to diffusion of copper in the copper film into a semiconductor film of the transistor.
  • a silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor, and as another material, an oxide semiconductor has attracted attention (see Patent Document 1).
  • Patent Document 1 Japanese Published Patent Application No. 2007-123861
  • a transistor using an oxide semiconductor film in which a copper film is used for a wiring, a signal line, or the like and a barrier film is used to suppress diffusion of copper in the copper film has had a problem in that electrical characteristics of the oxide semiconductor film deteriorate, the number of masks for the transistor using the oxide semiconductor film is increased, or the manufacturing cost of the transistor using the oxide semiconductor film is increased.
  • an object of one embodiment of the present invention is to provide a novel semiconductor device in which a metal film containing copper (Cu) is used for a wiring, a signal line, or the like in a transistor using an oxide semiconductor film.
  • Another object of one embodiment of the present invention is to provide a method for manufacturing a semiconductor device in which a metal film containing copper (Cu) is used for a wiring, a signal line, or the like in a transistor using an oxide semiconductor film.
  • Another object of one embodiment of the present invention is to provide a novel semiconductor device in which a metal film containing copper (Cu) in a transistor using an oxide semiconductor film has a favorable shape.
  • Another object of one embodiment of the present invention is to provide a novel semiconductor device or a method for manufacturing the novel semiconductor device.
  • One embodiment of the present invention is a semiconductor device including an oxide semiconductor film having conductivity on an insulating surface and a first conductive film in contact with the oxide semiconductor film having conductivity.
  • the first conductive film includes a Cu-X alloy film (Xis Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti).
  • Another embodiment of the present invention is a semiconductor device including an oxide semiconductor film having conductivity on an insulating surface and a first conductive film in contact with the oxide semiconductor film having conductivity.
  • the hydrogen concentration in the oxide semiconductor film having conductivity is higher than or equal to 8 x 10 19 atoms/cm 3 .
  • the first conductive film includes a Cu-X alloy film (Xis Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti).
  • Another embodiment of the present invention is a semiconductor device including an oxide semiconductor film having conductivity on an insulating surface and a first conductive film in contact with the oxide semiconductor film having conductivity.
  • the resistivity of the oxide semiconductor film having conductivity is higher than or equal to 1 x 10 ⁇ 3 Qcm and lower than 1 x 10 4 Qcm.
  • the first conductive film includes a Cu-X alloy film (Xis Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti).
  • the first conductive film may be a pair of conductive films, and the oxide semiconductor film having conductivity and the pair of conductive films in contact with the oxide semiconductor film having conductivity may serve as a resistor.
  • the semiconductor device of one embodiment of the present invention includes an insulating film in contact with the oxide semiconductor film having conductivity and the first conductive film, and a second conductive film in contact with the insulating film and overlapping with the oxide semiconductor film having conductivity with the insulating film provided therebetween.
  • the oxide semiconductor film having conductivity, the first conductive film, the insulating film, and the second conductive film may serve as a capacitor.
  • the insulating film may include a nitride insulating film.
  • the first conductive film includes a Cu-Mn alloy film.
  • the first conductive film is a stack of a Cu-Mn alloy film and a Cu film over the Cu-Mn alloy film.
  • the first conductive film is a stack of a first Cu-Mn alloy film, a Cu film over the first Cu-Mn alloy film, and a second Cu-Mn alloy film over the Cu film.
  • a coating film including a compound containing X may be provided on the outer periphery of the first conductive film.
  • the first conductive film includes a Cu-Mn alloy film
  • manganese oxide may be provided on the outer periphery of the first conductive film.
  • the oxide semiconductor film having conductivity includes a crystal part, and a c-axis of the crystal part may be parallel to a normal vector of the surface where the oxide semiconductor film is formed.
  • the oxide semiconductor film having conductivity may include an In- -Zn oxide ( is Al, Ga, Y, Zr, Sn, La, Ce, or Nd).
  • a novel semiconductor device in which a metal film containing copper is used for a wiring, a signal line, or the like in a transistor using an oxide semiconductor film can be provided.
  • a method for manufacturing a semiconductor device in which a metal film containing copper is used for a wiring, a signal line, or the like in a transistor using an oxide semiconductor film can be provided.
  • a novel semiconductor device in which a shape of a metal film containing copper is favorable in a transistor using an oxide semiconductor film can be provided.
  • a novel semiconductor device of which productivity is improved can be provided.
  • a novel semiconductor device or a method for manufacturing the novel semiconductor device can be provided.
  • FIGS. 1A to IE are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 2 A to 2D are cross-sectional views illustrating one embodiment of a method for manufacturing a semiconductor device of the present invention
  • FIGS. 3A to 3D are cross-sectional views illustrating one embodiment of a method for manufacturing a semiconductor device of the present invention.
  • FIGS. 4 A to 4C are cross-sectional views illustrating one embodiment of a method for manufacturing a semiconductor device of the present invention.
  • FIGS. 5 A to 5F are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 6 A to 6C are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 7 A to 7D are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 8 A and 8B are circuit diagrams each showing one embodiment of a semiconductor device of the present invention.
  • FIGS. 9 A and 9B are a top view and a cross-sectional view illustrating one embodiment of a semiconductor device of the present invention.
  • FIGS. 10A and 10B are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 11 A to l lC are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 12A to 12C are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 13A and 13B are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 14A to 14C are cross-sectional views illustrating embodiments of a semiconductor device of the present invention.
  • FIGS. 15A to 15C are a block diagram and circuit diagrams illustrating one embodiment of a display device
  • FIG. 16 is a top view illustrating one embodiment of a display device
  • FIG. 17 is a cross-sectional view illustrating one embodiment of a display device
  • FIGS. 18A to 18D are cross-sectional views illustrating one embodiment of a method for manufacturing a display device
  • FIGS. 19A to 19C are cross-sectional views illustrating one embodiment of a method for manufacturing a display device
  • FIGS. 20 A to 20C are cross-sectional views illustrating one embodiment of a method for manufacturing a display device
  • FIGS. 21 A and 21B are cross-sectional views illustrating one embodiment of a method for manufacturing a display device
  • FIG. 22 is a cross-sectional view illustrating one embodiment of a display device
  • FIG. 23 is a cross-sectional view illustrating one embodiment of a display device
  • FIG. 24 is a cross-sectional view illustrating one embodiment of a display device
  • FIG. 25 is a cross-sectional view illustrating one embodiment of a display device
  • FIGS. 26 A and 26B are cross-sectional views each illustrating one embodiment of a transistor
  • FIG. 27 is a top view illustrating one embodiment of a display device
  • FIG. 28 is a cross-sectional view illustrating one embodiment of a display device
  • FIGS. 29 A to 29C are cross-sectional views illustrating one embodiment of a method for manufacturing a display device
  • FIGS. 30A to 30C are cross-sectional views illustrating one embodiment of a method for manufacturing a display device
  • FIG. 31 is a cross-sectional view illustrating one embodiment of a display device
  • FIG. 32 is a cross-sectional view illustrating one embodiment of a display device
  • FIGS. 33A to 33C are cross-sectional views illustrating one embodiment of a method for manufacturing a display device
  • FIGS. 34A and 34B are cross-sectional views each illustrating one embodiment of a display device
  • FIG. 35 is a cross-sectional view illustrating one embodiment of a display device
  • FIG. 36 is a cross-sectional view illustrating one embodiment of a display device
  • FIGS. 37A to 37D are Cs-corrected high-resolution TEM images of a cross section of a CAAC-OS and a cross-sectional schematic view of a CAAC-OS;
  • FIGS. 38Ato 38D are Cs-corrected high -resolution TEM images of a plane of a CAAC-OS
  • FIGS. 39A to 39C show structural analysis of a CAAC-OS and a single crystal oxide semiconductor by XRD;
  • FIGS. 40A and 40B show electron diffraction patterns of a CAAC-OS
  • FIG. 41 shows a change of crystal parts of an In-Ga-Zn oxide owing to electron irradiation
  • FIGS. 42A and 42B are schematic views showing deposition models of a CAAC-OS and an nc-OS;
  • FIGS. 43 A to 43C show an InGaZn0 4 crystal and a pellet
  • FIGS. 44 A to 44D are schematic views illustrating a deposition model of a CAAC-OS
  • FIGS. 45A and 45B illustrate an InGaZn0 4 crystal
  • FIGS. 46A and 46B show a structure and the like of InGaZn0 4 before collision of an atom
  • FIGS. 47A and 47B show a structure and the like of InGaZn0 4 after collision of an atom
  • FIGS. 48A and 48B show trajectories of atoms after collision of atoms
  • FIGS. 49A and 49B are cross-sectional HAADF-STEM images of a CAAC-OS and a target;
  • FIG. 50 shows temperature dependence of resistivity of an oxide semiconductor film
  • FIG. 51 illustrates a display module
  • FIGS. 52 A to 52E are each an external view of an electronic device of one embodiment.
  • FIGS. 53A and 53B show a STEM image of Sample and a result of EDX analysis.
  • a transistor is an element having at least three terminals of a gate, a drain, and a source.
  • the transistor has a channel region between a drain (a drain terminal, a drain region, or a drain electrode layer) and a source (a source terminal, a source region, or a source electrode layer), and current can flow through the drain, the channel region, and the source.
  • a drain a drain terminal, a drain region, or a drain electrode layer
  • a source a source terminal, a source region, or a source electrode layer
  • the expression “electrically connected” includes the case where components are connected through an "object having any electric function".
  • an object having any electric function there is no particular limitation on an “object having any electric function” as long as electric signals can be transmitted and received between components that are connected through the object.
  • Examples of an “object having any electric function” are a switching element such as a transistor, a resistor, an inductor, a capacitor, and elements with a variety of functions as well as an electrode and a wiring.
  • FIGS. lA to IE a semiconductor device of one embodiment of the present invention is described with reference to FIGS. lA to IE, FIGS. 2A to 2D, FIGS. 3 A to 3D, FIGS. 4A to 4C, FIGS. 5A to 5F, and FIGS. 6A to 6C.
  • a structure of an oxide semiconductor film having conductivity and a conductive film in contact with the oxide semiconductor film and a manufacturing method thereof are described.
  • the oxide semiconductor film having conductivity serves as an electrode or a wiring.
  • FIGS. 1A to IE are cross-sectional views of an oxide semiconductor film having conductivity and a conductive film in contact with the oxide semiconductor film which are included in a semiconductor device.
  • an insulating film 153, an oxide semiconductor film 155b having conductivity over the insulating film 153, and a conductive film 159 in contact with the oxide semiconductor film 155b having conductivity are formed over a substrate 151.
  • an insulating film 157 may be formed over the insulating film 153, the oxide semiconductor film 155b having conductivity, and the conductive film 159.
  • the oxide semiconductor film 155b having conductivity may be formed over an insulating film 157a.
  • an insulating film 153a can be provided over the oxide semiconductor film 155b having conductivity and the conductive film 159.
  • the oxide semiconductor film 155b having conductivity is typically formed of a metal oxide film such as an In-Ga oxide film, an In-Zn oxide film, or an In-M-Zn oxide film (M is Al, Ga, Y, Zr, Sn, La, Ce, or Nd). Note that the oxide semiconductor film 155b having conductivity has a light-transmitting property.
  • the proportions of In and M when summation of In and M is assumed to be 100 atomic% are preferably as follows: the atomic percentage of In is greater than 25 atomic% and the atomic percentage of M is less than 75 atomic%, or further preferably, the atomic percentage of In is greater than 34 atomic% and the atomic percentage of Mis less than 66 atomic%.
  • the energy gap of the oxide semiconductor film 155b having conductivity is 2 eV or more, preferably 2.5 eV or more, further preferably 3 eV or more.
  • the thickness of the oxide semiconductor film 155b having conductivity is greater than or equal to 3 nm and less than or equal to 200 nm, preferably greater than or equal to 3 nm and less than or equal to 100 nm, further preferably greater than or equal to 3 nm and less than or equal to 50 nm.
  • the oxide semiconductor film 155b having conductivity is an In-M-Zn oxide film (M is Al, Ga, Y, Zr, Sn, La, Ce, or Nd), it is preferable that the atomic ratio of metal elements of a sputtering target used for forming the In-M-Zn oxide film satisfy In > M and Zn > M.
  • the oxide semiconductor film 155b having conductivity may have a non-single-crystal structure, for example.
  • the non-single crystal structure includes a c-axis aligned crystalline oxide semiconductor (CAAC-OS) described later, a polycrystalline structure, a microcrystalline structure described later, and an amorphous structure, for example.
  • CAAC-OS c-axis aligned crystalline oxide semiconductor
  • the amorphous structure has the highest density of defect levels
  • the CAAC-OS has the lowest density of defect levels.
  • the oxide semiconductor film 155b having conductivity may be a mixed film including two or more of the following: a region having an amorphous structure, a region having a microcrystalline structure, a region having a polycrystalline structure, a CAAC-OS region, and a region having a single-crystal structure.
  • the mixed film has a single-layer structure including, for example, two or more of a region having an amorphous structure, a region having a microcrystalline structure, a region having a polycrystalline structure, a CAAC-OS region, and a region having a single-crystal structure in some cases.
  • the mixed film has a stacked-layer structure of two or more of a region having an amorphous structure, a region having a microcrystalline structure, a region having a polycrystalline single layer structure, a CAAC-OS region, and a region having a single-crystal structure in some cases.
  • the insulating film 157 and the insulating film 157a are preferably formed of a film containing hydrogen, typically, a silicon nitride film containing hydrogen.
  • a film containing hydrogen typically, a silicon nitride film containing hydrogen.
  • the oxide semiconductor film 155b having conductivity includes an impurity.
  • Hydrogen is given as an example of the impurity included in the oxide semiconductor film 155b having conductivity.
  • the impurity boron, phosphorus, nitrogen, tin, antimony, a rare gas element, alkali metal, alkaline earth metal, or the like may be included.
  • the hydrogen concentration in the oxide semiconductor film 155b having conductivity is higher than or equal to 8 x 10 19 atoms/cm 3 , preferably higher than or equal to 1 20 3 l to 5 20 x 10 atoms/cm , further preferably higher than or equa x 10 atoms/cm 3 .
  • the hydrogen concentration in the oxide semiconductor film 155b having conductivity is lower than or equal to 20 atomic%, preferably lower than or equal to 1 x 10 22 atoms/cm 3 . Note that the concentration of hydrogen in the oxide semiconductor film 155b is measured by secondary ion mass spectrometry (SIMS) or hydrogen forward scattering (HFS).
  • the oxide semiconductor film 155b having conductivity exhibits conductivity.
  • the resistivity of the oxide semiconductor film 155b having conductivity is preferably higher than or equal to 1 x 10 ⁇ 3 Qcm and lower than 1 x 10 4 Qcm, further preferably higher than or equal to 1 x 10 ⁇ 3 Qcm and lower than 1 x 10 "1 Qcm.
  • the oxide semiconductor film 155b having conductivity includes defects in addition to impurities.
  • the oxide semiconductor film 155b having conductivity is typically a film in which defects are generated by releasing oxygen by heat treatment in vacuum in the formation process, a film in which defects are generated by adding a rare gas, or a film in which defects are generated by plasma exposure in the deposition process or the etching process of the conductive film 159.
  • an oxygen vacancy is given as an example of the defect included in the oxide semiconductor film 155b having conductivity.
  • oxide semiconductors When hydrogen is added to an oxide semiconductor including oxygen vacancies, hydrogen enters oxygen vacancies and forms a donor level in the vicinity of the conduction band. As a result, the conductivity of the oxide semiconductor is increased, so that the oxide semiconductor becomes a conductor.
  • An oxide semiconductor having become a conductor can be referred to as an oxide conductor. That is, the oxide semiconductor film 155b having conductivity can be formed of an oxide conductor film.
  • Oxide semiconductors generally have a visible light transmitting property because of their large energy gap.
  • An oxide conductor is an oxide semiconductor having a donor level in the vicinity of the conduction band. Therefore, the influence of absorption due to the donor level is small, and an oxide conductor has a visible light transmitting property comparable to that of an oxide semiconductor.
  • the conductive film 159 preferably includes at least a Cu-X alloy film (Xis Mn,
  • the conductive film 159 preferably has a single-layer structure of the Cu-X alloy film or a stacked-layer structure including the Cu-X alloy film.
  • the stacked-layer structure including the Cu-X alloy film a stacked-layer structure of the Cu-X alloy film and a conductive film including a low-resistance material such as copper (Cu), aluminum (Al), gold (Au), or silver (Ag), an alloy thereof, or a compound containing any of these materials as a main component (hereinafter referred to as a conductive film including a low-resistance material) is given.
  • the conductive film 159 has a stacked-layer structure of a conductive film
  • the Cu-X alloy film is used as the conductive film 159a and the conductive film including a low-resistance material is used as the conductive film 159b.
  • the conductive film 159 also serves as a lead wiring or the like.
  • the conductive film 159 includes the conductive film 159a using the Cu-X alloy film and the conductive film 159b using the conductive film including a low-resistance material, whereby even in the case where a large substrate is used as the substrate 151, a semiconductor device in which wiring delay is suppressed can be manufactured.
  • the conductive film 159 including the Cu-X alloy film is formed over the oxide semiconductor film 155b having conductivity, whereby the adhesion between the oxide semiconductor film 155b having conductivity and the conductive film 159 can be increased and the contact resistance therebetween can be reduced.
  • FIG. ID shows an enlarged view of a region where the oxide semiconductor film 155b having conductivity is in contact with the conductive film 159.
  • a coating film 156 is formed at an interface between the oxide semiconductor film 155b having conductivity and the conductive film 159 in some cases.
  • the coating film 156 is formed using a compound including X.
  • the compound including X is formed by reaction between X in the Cu-X alloy film included in the conductive film 159 and an element included in the oxide semiconductor film 155b having conductivity or the insulating film 157.
  • oxide including X oxide including X
  • nitride including X silicide including X
  • carbide including X examples of the oxide including X, X oxide, In-X oxide, Ga-X oxide, In-Ga-X oxide, In-Ga-Zn-X oxide, and the like are given.
  • the coating film 156 serving as a blocking film against Cu entry of Cu in the Cu-X alloy film into the oxide semiconductor film 155b having conductivity can be suppressed.
  • the conductive film 159a As an example of the conductive film 159a, a Cu-Mn alloy film is used, whereby the adhesion between the conductive film 159a and the underlying oxide semiconductor film 155b having conductivity can be increased. Furthermore, by using the Cu-Mn alloy film, a favorable ohmic contact can be obtained between the conductive film 159 and the oxide semiconductor film 155b having conductivity.
  • the coating film 156 is formed in the following manner in some cases: after the formation of the Cu-Mn alloy film, by heat treatment at a temperature higher than or equal to 150 °C and lower than or equal to 450 °C, preferably at a temperature higher than or equal to 250 °C and lower than or equal to 350 °C or by forming the insulating film 157 while being heated, Mn in the Cu-Mn alloy film is segregated at the interface between the oxide semiconductor film 155b having conductivity and the conductive film 159a.
  • the coating film 156 can include Mn oxide formed by oxidation of the Mn or In-Mn oxide, Ga-Mn oxide, In-Ga-Mn oxide, In-Ga-Zn-Mn oxide, or the like, which is formed by reaction between the segregated Mn and a constituent element in the oxide semiconductor film 155b having conductivity. With the coating film 156, the adhesion between the oxide semiconductor film 155b having conductivity and the conductive film 159a is improved. Furthermore, with the segregation of Mn in the Cu-Mn alloy film, part of the Cu-Mn alloy film becomes a pure Cu film, so that the conductive film 159a can obtain high conductivity.
  • a coating film 156a is formed on at least one of the bottom surface, side surface, and top surface of the conductive film 159, preferably on the outer periphery of the conductive film 159 in some cases.
  • the coating film 156a is formed using a compound including X.
  • the compound including X is formed by reaction between X in the Cu- alloy film included in the conductive film 159 and an element included in the oxide semiconductor film 155b having conductivity or the insulating film 157.
  • oxide including X, nitride including X, silicide including X, carbide including X, and the like are given.
  • an oxide insulating film is formed as the insulating film 157
  • an oxide of a low-resistance material is formed in a region where the coating film 156a is in contact with the conductive film 159b.
  • X in the Cu-X alloy film is included in the region where the coating film 156a is in contact with the conductive film 159b in some cases. This is probably due to an attachment of a residue generated in the etching of the conductive film 159a, the attachment of the residue in the formation of the insulating film 157, the attachment of the residue at the heat treatment, or the like.
  • Xm ' the Cu-X alloy film is oxidized to oxide in some cases.
  • a copper (Cu) film is preferably used as the conductive film 159b, because the thickness of the conductive film 159b can be increased to improve the conductivity of the conductive film 159.
  • the copper (Cu) film refers to pure copper (Cu), and the purity is preferably 99 % or higher. Note that the pure copper (Cu) may include an impurity element at several percent.
  • the conductive film 159 includes the Cu-X alloy film, whereby a semiconductor device in which entry of the copper (Cu) into the oxide semiconductor film 155b having conductivity is suppressed and a wiring has high conductivity can be obtained.
  • the substrate 151 a variety of substrates can be used without particular limitation.
  • the substrate include a semiconductor substrate (e.g., a single crystal substrate or a silicon substrate), a silicon on insulator (SOI) substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate including stainless steel foil, a tungsten substrate, a substrate including tungsten foil, a flexible substrate, an attachment film, paper including a fibrous material, and a base material film.
  • a semiconductor substrate e.g., a single crystal substrate or a silicon substrate
  • SOI silicon on insulator
  • glass substrate e.g., a quartz substrate, a plastic substrate
  • metal substrate e.g., a stainless steel substrate, a substrate including stainless steel foil, a tungsten substrate, a substrate including tungsten foil, a flexible substrate, an attachment film, paper including a fibrous material, and a base material film.
  • a glass substrate a barium
  • Examples of a flexible substrate, an attachment film, a base material film, and the like are as follows: plastic typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyether sulfone (PES); a synthetic resin such as acrylic; polypropylene; polyester; polyvinyl fluoride; polyvinyl chloride; polyamide; polyimide; aramid; epoxy; an inorganic vapor deposition film; and paper.
  • PET polyethylene terephthalate
  • PEN polyethylene naphthalate
  • PES polyether sulfone
  • a synthetic resin such as acrylic; polypropylene; polyester; polyvinyl fluoride; polyvinyl chloride; polyamide; polyimide; aramid; epoxy; an inorganic vapor deposition film; and paper.
  • semiconductor substrates, single crystal substrates, SOI substrates, or the like enables the manufacture of small-sized transistors with a small variation in characteristics, size, shape, or the like and with
  • a flexible substrate may be used as the substrate 151, and a semiconductor element may be formed directly on the flexible substrate.
  • a separation layer may be provided between the substrate 151 and the semiconductor element. The separation layer can be used when part or the whole of a semiconductor element formed over the separation layer is separated from the substrate 151 and transferred onto another substrate. In such a case, the semiconductor element can be transferred onto a substrate having low heat resistance or a flexible substrate as well.
  • a stack including inorganic films, such as a tungsten film and a silicon oxide film, or an organic resin film of polyimide or the like formed over a substrate can be used, for example.
  • Examples of a substrate to which a transistor is transferred include, in addition to the above-described substrates over which transistors can be formed, a paper substrate, a cellophane substrate, an aramid film substrate, a polyimide film substrate, a stone substrate, a wood substrate, a cloth substrate (including a natural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra, rayon, or regenerated polyester), or the like), a leather substrate, a rubber substrate, and the like.
  • the use of such a substrate enables formation of a transistor with excellent properties, a transistor with low power consumption, or a device with high durability, high heat resistance, or a reduction in weight or thickness.
  • insulating films 153 and 153a a single layer or a stacked layer including an oxide insulating film such as a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, a hafnium oxide film, a gallium oxide film, or a Ga-Zn-based metal oxide film may be used.
  • an oxide insulating film such as a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, a hafnium oxide film, a gallium oxide film, or a Ga-Zn-based metal oxide film.
  • the insulating films 153 and 153a may be formed using a high-k material such as hafnium silicate (HfSiO x ), hafnium silicate to which nitrogen is added (HfSi x O y N z ), hafnium aluminate to which nitrogen is added (HfAl x O y N z ), hafnium oxide, or yttrium oxide.
  • hafnium silicate hafnium silicate to which nitrogen is added
  • hafSi x O y N z hafnium aluminate to which nitrogen is added
  • hafAl x O y N z hafnium oxide
  • hafnium oxide or yttrium oxide.
  • the insulating films 153 and 153a can be formed using a nitride insulating film such as a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, or an aluminum nitride oxide film.
  • a nitride insulating film such as a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, or an aluminum nitride oxide film.
  • the substrate 151 is prepared.
  • a glass substrate is used as the substrate 151.
  • the insulating film 153 is formed over the substrate 151, and an oxide semiconductor film 155 is formed over the insulating film 153. Then, a rare gas 154 such as helium, neon, argon, krypton, or xenon is added to the oxide semiconductor film 155.
  • a rare gas 154 such as helium, neon, argon, krypton, or xenon is added to the oxide semiconductor film 155.
  • the insulating film 153 can be formed by a sputtering method, a CVD method, a vacuum evaporation method, a pulsed laser deposition (PLD) method, a thermal CVD method, or the like.
  • a formation method of the oxide semiconductor film 155 is described below.
  • An oxide semiconductor film is formed by a sputtering method, a coating method, a pulsed laser deposition method, a laser ablation method, a thermal CVD method, or the like. Then, by forming a mask over the oxide semiconductor film through a photolithography process and etching the oxide semiconductor film with the mask, the oxide semiconductor film 155 can be formed.
  • a rare gas typically argon
  • an oxygen gas or a mixed gas of a rare gas and an oxygen gas
  • the proportion of an oxygen gas to a rare gas is preferably increased.
  • a target may be appropriately selected in accordance with the composition of the oxide semiconductor film to be formed.
  • the oxide semiconductor film is formed by a sputtering method at a substrate temperature higher than or equal to 150 °C and lower than or equal to 750 °C, preferably higher than or equal to 150 °C and lower than or equal to 450 °C, more preferably higher than or equal to 200 °C and lower than or equal to 350 °C
  • the oxide semiconductor film can be a CAAC-OS film.
  • the following conditions are preferably used.
  • the crystal state can be prevented from being broken by the impurities.
  • the impurity concentration e.g., hydrogen, water, carbon dioxide, and nitrogen
  • the impurity concentration in a deposition gas may be reduced.
  • a deposition gas whose dew point is -80 °C or lower, preferably -100 °C or lower is used.
  • an oxide semiconductor film e.g., an In-Ga-Zn-0 film is formed using a deposition apparatus employing ALD
  • an In(CH 3 ) 3 gas and an 0 3 gas are sequentially introduced plural times to form an In-0 layer
  • a Ga(CH 3 ) 3 gas and an 0 3 gas are introduced at a time to form a GaO layer
  • a Zn(CH 3 ) 2 gas and an 0 3 gas are introduced at a time to form a ZnO layer.
  • a mixed compound layer such as an In-Ga-0 layer, an In-Zn-0 layer, or a Ga-Zn-0 layer may be formed by mixing of these gases.
  • an H 2 0 gas which is obtained by bubbling with an inert gas such as Ar may be used instead of an 0 3 gas, it is preferable to use an 0 3 gas that does not contain H.
  • an In(CH 3 ) 3 gas an In(C 2 H 5 ) 3 may be used.
  • a Ga(CH 3 ) 3 gas a Ga(CH 3 ) 3 gas
  • Ga(C 2 H 5 ) 3 gas may be used. Furthermore, a Zn(CH 3 ) 2 gas may be used.
  • hydrogen, water, and the like may be released from the oxide semiconductor film 155 by heat treatment to reduce at least the hydrogen concentration in the oxide semiconductor film 155.
  • oxygen is released from the oxide semiconductor film 155, so that defects can be formed.
  • variation in hydrogen concentration in the oxide semiconductor film 155b formed later can be reduced.
  • the heat treatment is performed typically at a temperature higher than or equal to 250 °C and lower than or equal to 650 °C, preferably higher than or equal to 300 °C and lower than or equal to 500 °C.
  • the heat treatment is performed typically at a temperature higher than or equal to 300 °C and lower than or equal to 400 °C, preferably higher than or equal to 320 °C and lower than or equal to 370 °C, whereby warp or shrinking of a large-sized substrate can be reduced and yield can be improved.
  • An electric furnace, an RTA apparatus, or the like can be used for the heat treatment.
  • the heat treatment can be performed at a temperature of higher than or equal to the strain point of the substrate if the heating time is short.
  • the heat treatment time can be shortened and warp of the substrate during the heat treatment can be reduced, which is particularly preferable in a large-sized substrate.
  • the heat treatment may be performed under an atmosphere of nitrogen, oxygen, ultra-dry air (air in which a water content is 20 ppm or less, preferably 1 ppm or less, more preferably 10 ppb or less), or a rare gas (argon, helium, or the like).
  • the atmosphere of nitrogen, oxygen, ultra-dry air, or a rare gas preferably does not contain hydrogen, water, and the like.
  • the rare gas 154 helium, neon, argon, xenon, krypton, or the like can be used as appropriate. Furthermore, as methods for adding the rare gas 154 to the oxide semiconductor film 155, a doping method, an ion implantation method, and the like are given. Alternatively, the rare gas 154 can be added to the oxide semiconductor film 155 by exposing the oxide semiconductor film 155 to plasma including the rare gas 154.
  • an oxide semiconductor film 155a including defects can be formed.
  • the oxide semiconductor film 155a including defects is heated in an atmosphere including impurities.
  • the heat treatment is performed in an atmosphere including one or more of hydrogen, nitrogen, water vapor, and the like as the atmosphere including impurities.
  • the heat treatment is preferably performed under a condition for supplying impurities to the oxide semiconductor film, and typically performed at a heating temperature higher than or equal to 250 °C and lower than or equal to 350 °C. By performing heat treatment at 350 °C or lower, impurities can be supplied to the oxide semiconductor film while the release of the impurities from the oxide semiconductor film is minimized.
  • the heat treatment is preferably performed under a pressure higher than or equal to 0.1 Pa, further preferably higher than or equal to 0.1 Pa and lower than or equal to 101325 Pa, still further preferably higher than or equal to 1 Pa and lower than or equal to 133 Pa.
  • the oxide semiconductor film 155b having conductivity can be formed.
  • the oxide semiconductor film 155b having conductivity includes defects and impurities. By the effect of the defects and the impurities, the conductivity of the oxide semiconductor film 155b having conductivity is increased as compared to that of the oxide semiconductor film 155.
  • defects and impurities hydrogen enters an oxygen vacancy, whereby an electron serving as a carrier is generated.
  • bonding of part of hydrogen to oxygen bonded to a metal atom causes generation of an electron serving as a carrier.
  • the conductivity of the oxide semiconductor film is increased.
  • the oxide semiconductor film 155b having conductivity serves as an electrode or a wiring.
  • the oxide semiconductor film 155b having conductivity has a light-transmitting property. Thus, a light-transmitting electrode or a light-transmitting wiring can be formed.
  • the resistivity of the oxide semiconductor film 155b having conductivity is higher than that of the conductive film 159.
  • the conductive film 159 is preferably in contact with the oxide semiconductor film 155b.
  • the conductive film 159 is formed over the oxide semiconductor film 155b having conductivity.
  • a mask is formed over the conductive film including a low-resistance material by a photolithography process and the Cu-X alloy film and the conductive film including a low-resistance material are etched using the mask, whereby the conductive film 159 in which the conductive film 159a formed of the Cu-X alloy film and the conductive film 159b formed of the conductive film including a low-resistance material are stacked can be formed.
  • a dry etching method or a wet etching method can be used as appropriate.
  • a wet etching method is preferably used.
  • the Cu-X alloy film can be etched by a wet etching method; thus, when the Cu-X alloy film and the copper (Cu) film are stacked, the conductive film 159 in which the conductive film 159a formed of the Cu-X alloy film and the conductive film 159b formed of the conductive film including a low-resistance material are stacked can be formed in a single wet etching step.
  • an etchant used in the wet etching method an etchant containing an organic acid solution and hydrogen peroxide water, or the like is used.
  • the oxide semiconductor film having conductivity and the conductive film in contact with the oxide semiconductor film having conductivity can be formed.
  • a formation method of the oxide semiconductor film 155b having conductivity which is different from the method in FIGS. 2A to 2D is described with reference to FIGS. 3Ato 3D.
  • the insulating film 153 is formed over the substrate 151, and the oxide semiconductor film 155 is formed over the insulating film 153. Then, heat treatment is performed in vacuum. By performing heat treatment in vacuum, oxygen is released from the oxide semiconductor film 155, so that the oxide semiconductor film 155a including defects can be obtained as illustrated in FIG. 3B. Note that a typical example of the defects included in the oxide semiconductor film 155a is oxygen vacancies.
  • the heat treatment is preferably performed under a condition for releasing oxygen from the oxide semiconductor film, and typically performed at a temperature higher than or equal to 350 °C and lower than or equal to 800 °C, preferably higher than or equal to 450 °C and lower than or equal to 800 °C.
  • a temperature higher than or equal to 350 °C and lower than or equal to 800 °C preferably higher than or equal to 450 °C and lower than or equal to 800 °C.
  • heating is preferably performed in vacuum, typically under a pressure higher than or equal to 1 x 10 ⁇ 7 Pa and lower than or equal to 10 Pa, preferably higher than or equal to 1 x 10 ⁇ 7 Pa and lower than or equal to 1 Pa, further preferably higher than or equal to 1 x 10 ⁇ 7 Pa and lower than or equal to IE -1 Pa.
  • the oxide semiconductor film 155a including defects is heated in an atmosphere including impurities.
  • the heat treatment is performed in an atmosphere including one or more of hydrogen, nitrogen, water vapor, and the like as the atmosphere including impurities.
  • the oxide semiconductor film 155b having conductivity can be formed.
  • the conductive film 159 can be formed over the oxide semiconductor film 155b having conductivity (see FIG. 3D).
  • FIGS. 4 A to 4C A formation method of the oxide semiconductor film 155b having conductivity which is different from the methods in FIGS. 2A to 2D and FIGS. 3 A to 3D is described with reference to FIGS. 4 A to 4C.
  • the oxide semiconductor film 155 is formed over the insulating film 153.
  • the conductive film 159 is formed over the oxide semiconductor film 155 (see FIG. 4B).
  • the conductive film 159 the conductive film 159a and the conductive film 159b are formed.
  • the insulating film 157 including hydrogen is formed over the insulating film 153, the oxide semiconductor film 155, and the conductive film 159.
  • the insulating film 157 is formed by a sputtering method, a plasma CVD method, or the like.
  • the insulating film 157 may be formed while being heated. Alternatively, heat treatment may be performed after the insulating film 157 is formed.
  • the oxide semiconductor film 155 is damaged and defects are generated. Furthermore, the insulating film 157 is formed while heating or heat treatment is performed after the insulating film 157 is formed, whereby hydrogen included in the insulating film 157 moves to the oxide semiconductor film 155. As a result, as illustrated in FIG. 4C, the oxide semiconductor film 155b having conductivity can be formed. By the action of defects and impurities, the conductivity of the oxide semiconductor film 155b having conductivity is increased as compared to that of the oxide semiconductor film 155. Thus, the oxide semiconductor film 155b having conductivity serves as an electrode or a wiring.
  • Modification examples of the conductive film 159 are described with reference to FIGS. 5 A to 5F. Here, modification examples of the conductive film 159 in FIG. IB are shown; however, the modification examples can be used in the conductive film 159 in FIGS. lA and 1C as appropriate.
  • the conductive film 159a can be formed of a single layer of the Cu-X alloy film over the oxide semiconductor film 155b having conductivity.
  • the conductive film 159 can be formed over the oxide semiconductor film 155b having conductivity by stacking the conductive film 159a formed of the Cu-X alloy film, the conductive film 159b formed of the conductive film including a low-resistance material, and a conductive film 159c formed of the Cu-X alloy film.
  • the conductive film 159 includes the conductive film 159c formed of the Cu-X alloy film over the conductive film 159b formed of the conductive film including a low-resistance material
  • the conductive film 159c formed of the Cu-X alloy film serves as a protective film of the conductive film 159b including a low-resistance material; thus, the reaction of the conductive film 159b including a low-resistance material in the formation of the insulating film 157 can be prevented.
  • the oxide semiconductor film 155b having conductivity may be formed over the insulating film 157a formed of a film including hydrogen.
  • the insulating film 153a can be provided over the oxide semiconductor film 155b having conductivity and the conductive film 159.
  • FIGS. 5E and 5F show enlarged views of regions where the oxide semiconductor film 155b having conductivity is in contact with the conductive film 159 and the conductive film 159a respectively.
  • a coating film 156b is formed on at least one of the bottom surface, side surface, and top surface of the conductive film 159a, preferably on the outer periphery of the conductive film 159a in some cases.
  • the coating film 156b is formed using a compound including X.
  • the compound including X is formed by reaction between Xin the Cu-X alloy film included in the conductive film 159a and an element included in the oxide semiconductor film 155b having conductivity or the insulating film 157.
  • oxide including X, nitride including X, silicide including X, carbide including X, and the like are given.
  • a manganese oxide film is formed.
  • a coating film 156c is formed on at least one of the bottom surface, side surface, and top surface of the conductive film 159, preferably on the outer periphery of the conductive film 159 in some cases.
  • the coating film 156c is formed using a compound including X.
  • the compound including X is formed by reaction between X in the Cu-X alloy film included in the conductive film 159 and an element included in the oxide semiconductor film 155b having conductivity or the insulating film 157. In a region where the coating film 156c is in contact with the conductive film 159b, an oxide of the low-resistance material is formed.
  • X in the Cu-X alloy film is included in the region where the coating film 156c is in contact with the conductive film 159b in some cases. This is probably due to an attachment of a residue generated in the etching of the conductive film 159a or the conductive film 159c, the attachment of the residue in the formation of the insulating film 157, the attachment of the residue at the heat treatment, or the like. Furthermore, Xm ' the Cu-X alloy film is oxidized to oxide in some cases. Thus, in the case where a Cu-Mn alloy film is used as the conductive film 159b, as an example of the coating film 156c, a manganese oxide film is formed.
  • a single layer of the conductive film 159a formed of the Cu-X alloy film is provided between the insulating film 153 and the oxide semiconductor film 155b having conductivity.
  • the conductive film 159 having a two-layer structure is provided between the insulating film 153 and the oxide semiconductor film 155b having conductivity.
  • the conductive film 159 is formed by stacking the conductive film 159a formed of the Cu-X alloy film and the conductive film 159b formed of the conductive film including a low-resistance material.
  • the conductive film 159 having a three-layer structure is provided between the insulating film 153 and the oxide semiconductor film 155b having conductivity.
  • the conductive film 159 is formed by stacking the conductive film 159a formed of the Cu-X alloy film, the conductive film 159b formed of the conductive film including a low-resistance material, and the conductive film 159c formed of the Cu-X alloy film.
  • the conductive film 159c formed of the Cu-X alloy film When the conductive film 159c formed of the Cu-X alloy film is provided over the conductive film 159b formed of the conductive film including a low-resistance material in the conductive film 159, the conductive film 159c formed of the Cu-X alloy film serves as a protective film of the conductive film 159b including a low-resistance material; thus, the reaction of the conductive film 159b including a low-resistance material in the formation of the oxide semiconductor film 155b having conductivity can be prevented.
  • a resistor including the oxide semiconductor film having conductivity in Embodiment 1 is described with reference to FIGS. 7A to 7D, FIGS. 8A and 8B, FIGS. 9A and 9B, FIGS. lOA and 10B, and FIGS. HAto 11C.
  • FIGS. 7A to 7D are cross-sectional views of resistors included in a semiconductor device.
  • a resistor 160a in FIG. 7 A includes the oxide semiconductor film 155b having conductivity and a pair of conductive films 161 and 162 in contact with the oxide semiconductor film 155b having conductivity.
  • the oxide semiconductor film 155b having conductivity and the pair of conductive films 161 and 162 are provided over the insulating film 153 formed over the substrate 151.
  • each of the conductive films 161 and 162 may have a single layer structure or a stacked-layer structure of two or more layers.
  • the pair of conductive films 161 and 162 can be formed using a structure, a material, and a formation method similar to those of the conductive film 159 in Embodiment 1. That is, the pair of conductive films 161 and 162 includes the Cu-X alloy film.
  • the conductive film 161 has a stacked-layer structure of a conductive film 161a in contact with the oxide semiconductor film 155b having conductivity and a conductive film 161b in contact with the conductive film 161a
  • the conductive film 162 has a stacked-layer structure of a conductive film 162a in contact with the oxide semiconductor film 155b having conductivity and a conductive film 162b in contact with the conductive film 162a.
  • the conductive films 161a and 162a the Cu-X alloy film is used.
  • the conductive films 161b and 162b the conductive film including a low-resistance material is used.
  • the insulating film 157 made of a film including hydrogen may be formed over the insulating film 153, the oxide semiconductor film 155b having conductivity, and the pair of conductive films
  • the insulating film 153a can be provided over the oxide semiconductor film 155b having conductivity and the pair of conductive films 161 and 162.
  • the resistivity of the oxide semiconductor film 155b having conductivity is higher than those of the pair of conductive films 161 and 162 including the Cu-X film.
  • they serve as a resistor.
  • the oxide semiconductor film 155b having conductivity includes defects and impurities. By the effect of the defects and the impurities, the conductivity of the oxide semiconductor film 155b having conductivity is increased. Furthermore, the oxide semiconductor film 155b having conductivity has a light-transmitting property. As a result, a light-transmitting resistor can be formed.
  • the pair of conductive films 161 and 162 including the Cu-X alloy film is formed over the oxide semiconductor film 155b having conductivity, whereby the adhesion between the oxide semiconductor film 155b having conductivity and the pair of conductive films 161 and 162 can be increased and the contact resistance therebetween can be reduced.
  • FIG. 7D shows an enlarged view of a region where the oxide semiconductor film 155b having conductivity is in contact with the conductive film 161.
  • the coating film 156 including X in the Cu-X alloy film is formed at an interface between the oxide semiconductor film 155b having conductivity and the conductive film 161a in some cases.
  • the coating film 156 serving as a blocking film against Cu entry of Cu in the Cu-X alloy film into the oxide semiconductor film 155b having conductivity can be suppressed.
  • a coating film such as the coating film 156a is formed on the periphery of the conductive films 161 and 162 in some cases, similarly to the case of the conductive film 159 in Embodiment 1.
  • a protection circuit using the resistor in this embodiment is described with reference to FIGS. 8A and 8B.
  • a display device is used as a semiconductor device here, a protection circuit can be used in another semiconductor device.
  • FIG. 8 A illustrates a specific example of a protection circuit 170a included in the semiconductor device.
  • the protection circuit 170a illustrated in FIG. 8 A includes a resistor 173 between a wiring 171 and a wiring 172, and a transistor 174 that is diode-connected.
  • the resistor 173 is connected to the transistor 174 in series, so that the resistor 173 can control the value of current flowing through the transistor 174 or can function as a protective resistor of the transistor 174 itself.
  • the wiring 171 is, for example, a lead wiring from a scan line, a data line, or a terminal portion included in a display device to a driver circuit portion.
  • the wiring 172 is, for example, a wiring that is supplied with a potential (VDD, VSS, or G D) of a power supply line for supplying power to a gate driver or a source driver.
  • the wiring 172 is a wiring that is supplied with a common potential (common line).
  • the wiring 172 is preferably connected to the power supply line for supplying power to a scan line driver circuit, in particular, to a wiring for supplying a low potential. This is because a gate signal line has a low-level potential in most periods, and thus, when the wiring 172 also has a low-level potential, current leaked from the gate signal line to the wiring 172 can be reduced in a normal operation.
  • resistor 173 illustrated in FIG. 8 A is connected in series to the diode-connected transistor, the resistor 173 can be connected in parallel to the diode-connected transistor without being limited to the example in FIG. 8A.
  • FIG. 8B illustrates a protection circuit including a plurality of transistors and a plurality of resistors.
  • a protection circuit 170b illustrated in FIG. 8B includes transistors 174a, 174b, 174c, and 174d and resistors 173a, 173b, and 173c.
  • the protection circuit 170b is provided between a set of wirings 175, 176, and 177 and another set of wirings 175, 176, and 177.
  • the wirings 175, 176, and 177 are connected to one or more of a scan line driver circuit, a signal line driver circuit, and a pixel portion.
  • a first terminal serving as a source electrode of the transistor 174a is connected to a second terminal serving as a gate electrode of the transistor 174a
  • a third terminal serving as a drain electrode of the transistor 174a is connected to a wiring 177.
  • a first terminal serving as a source electrode of the transistor 174b is connected to a second terminal serving as a gate electrode of the transistor 174b, and a third terminal serving as a drain electrode of the transistor 174b is connected to the first terminal of the transistor 174a.
  • a first terminal serving as a source electrode of the transistor 174c is connected to a second terminal serving as a gate electrode of the transistor 174c, and a third terminal serving as a drain electrode of the transistor 174c is connected to the first terminal of the transistor 174b.
  • a first terminal serving as a source electrode of the transistor 174d is connected to a second terminal serving as a gate electrode of the transistor 174d, and a third terminal serving as a drain electrode of the transistor 174d is connected to the first terminal of the transistor 174c.
  • the resistors 173a and 173c are provided in the wiring 177.
  • the resistor 173b is provided between the wiring 176 and the first terminal of the transistor 174b and the third terminal of the transistor 174c.
  • the wiring 175 can be used as a power supply line to which the low power supply potential VSS is applied, for example.
  • the wiring 176 can be used as a common line, for example.
  • the wiring 177 can be used as a power supply line to which the high power supply potential VDD is applied.
  • FIGS. 9A and 9B illustrate an example of a resistor 160d.
  • FIG. 9A is a top view of the resistor 160d
  • FIG. 9B is a cross-sectional view taken along dashed-dotted line A-B in FIG. 9 A.
  • the top surface of an oxide semiconductor film 155c having conductivity has a zigzag shape, whereby the resistance of the resistor can be controlled.
  • the protection circuit 170b includes the plurality of transistors that are diode-connected and the plurality of resistors.
  • the protection circuit 170b can include diode-connected transistors and resistors that are combined in parallel.
  • the semiconductor device can have an enhanced resistance to overcurrent due to electrostatic discharge (ESD). Therefore, a semiconductor device with improved reliability can be provided.
  • ESD electrostatic discharge
  • the resistor can be used as the protection circuit and the resistance of the resistor can be controlled arbitrarily, the diode-connected transistor or the like that is used as the protection circuit can also be protected.
  • each of the conductive films 161a and 162a can be formed of a single layer of the Cu-X alloy film over the oxide semiconductor film 155b having conductivity.
  • the pair of conductive films 161 and 162 can have a three-layer structure.
  • the conductive film 161 has a stacked-layer structure of the conductive film 161a in contact with the oxide semiconductor film 155b having conductivity, the conductive film 161b in contact with the conductive film 161a, and a conductive film 161c in contact with the conductive film 161b.
  • the conductive film 162 has a stacked-layer structure of the conductive film 162a in contact with the oxide semiconductor film 155b having conductivity, the conductive film 162b in contact with the conductive film 162a, and a conductive film 162c in contact with the conductive film 162b.
  • the pair of conductive films 161 and 162 includes the conductive films
  • the conductive films 161c and 162c formed of the Cu-X alloy film serve as protective films of the conductive films 161b and 162b including a low-resistance material; thus, the reaction of the conductive films 161b and 162b including a low-resistance material in the formation of the insulating film 157 can be prevented.
  • a coating film such as the coating films 156b and 156c is formed on the periphery of the conductive films 161 and 162 in some cases, similarly to the case of the conductive film 159 in Embodiment 1.
  • a resistor 160g in FIG. 11 A includes the pair of conductive films 163a and 164a formed of the single-layer Cu-X alloy film between the insulating film 153 and the oxide semiconductor film 155b having conductivity.
  • the pair of conductive films 163 and 164 is provided between the insulating film 153 and the oxide semiconductor film 155b having conductivity and has a two-layer structure.
  • the conductive film 163 is formed by stacking the conductive film 163a formed of the Cu-X alloy film and the conductive film 163b formed of the conductive film including a low-resistance material.
  • the conductive film 164 is formed by stacking the conductive film 164a formed of the Cu-X alloy film and the conductive film 164b formed of the conductive film including a low-resistance material.
  • the pair of conductive films 163 and 164 is provided between the insulating film 153 and the oxide semiconductor film 155b having conductivity and has a three-layer structure.
  • the conductive film 163 is formed by stacking the conductive film 163a formed of the Cu-X alloy film, the conductive film 163b formed of the conductive film including a low-resistance material, and the conductive film 163c formed of the Cu-X alloy film.
  • the conductive film 164 is formed by stacking the conductive film 164a formed of the Cu-X alloy film, the conductive film 164b formed of the conductive film including a low-resistance material, and the conductive film 164c formed of the Cu-X alloy film.
  • the conductive films 163c and 164c formed of the Cu-X alloy film serve as protective films of the conductive films 163b and 164b formed of a conductive film including a low-resistance material; thus, the reaction of the conductive films 163b and 164b including a low-resistance material in the formation of the oxide semiconductor film 155b having conductivity and the insulating film 157 can be prevented.
  • a coating film such as the coating films 156, 156a, 156b and 156c is formed on the periphery of the pair of conductive films 163 and 164 in some cases, similarly to the case of the conductive film 159 in Embodiment 1.
  • FIGS. 12A to 12C a capacitor including the oxide semiconductor film having conductivity in Embodiment 1 is described with reference to FIGS. 12A to 12C, FIGS. 13 A and 13B, and FIGS. 14A to 14C.
  • FIGS. 12A to 12C are cross-sectional views of capacitors included in a semiconductor device.
  • a capacitor 180a in FIG. 12A includes the oxide semiconductor film 155b having conductivity, the insulating film 157 in contact with the oxide semiconductor film 155b having conductivity, and a conductive film 181 overlapping with the oxide semiconductor film 155b with the insulating film 157 therebetween. Furthermore, a conductive film serving as a lead wiring may be in contact with the oxide semiconductor film 155b having conductivity or the conductive film 181. Here, the conductive film 159 in contact with the oxide semiconductor film 155b having conductivity is the film serving as a lead wiring. The oxide semiconductor film 155b having conductivity, the insulating film 157, and the conductive film 159 are provided over the insulating film 153 formed over the substrate 151.
  • the conductive film 159 may have a single layer structure or a stacked-layer structure of two or more layers.
  • the conductive film 159 can be formed using a structure, a material, and a formation method similar to those of the conductive film 159 in Embodiment 1. That is, the conductive film 159 includes the Cu-X alloy film.
  • the conductive film 159 has a stacked-layer structure of a conductive film 159a in contact with the oxide semiconductor film 155b having conductivity and a conductive film 159b in contact with the conductive film 159a.
  • the conductive film 159a the Cu-X alloy film is used.
  • the conductive film 159b the conductive film including a low-resistance material is used.
  • the oxide semiconductor film 155b having conductivity and the conductive film 159 may be formed over the insulating film 157a.
  • the insulating film 153a can be provided between the oxide semiconductor film 155b having conductivity and the conductive film 181.
  • the conductive film 181 is formed to have a single-layer structure or a stacked-layer structure including any of metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, iron, cobalt, silver, tantalum, and tungsten and an alloy containing any of these metals as its main component.
  • metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, iron, cobalt, silver, tantalum, and tungsten and an alloy containing any of these metals as its main component.
  • a structure and a material similar to those of the conductive film 159 can be used as appropriate.
  • a light-transmitting conductive film can be used as the conductive film 181.
  • a light-transmitting conductive film an indium oxide film containing tungsten oxide, an indium zinc oxide film containing tungsten oxide, an indium oxide film containing titanium oxide, an indium tin oxide film containing titanium oxide, an indium tin oxide (hereinafter, referred to as ITO) film, an indium zinc oxide film, an indium tin oxide film to which silicon oxide is added, and the like are given.
  • the oxide semiconductor film 155b having conductivity includes defects and impurities. By the action of the defects and the impurities, the conductivity of the oxide semiconductor film 155b having conductivity is increased. Furthermore, the oxide semiconductor film 155b having conductivity has a light-transmitting property. A light-transmitting conductive film is used as the conductive film 181, whereby a light-transmitting capacitor can be formed.
  • the conductive film 159 including the Cu-X alloy film is formed over the oxide semiconductor film 155b having conductivity, whereby the adhesion between the oxide semiconductor film 155b having conductivity and the conductive film 159 can be increased and the contact resistance between them can be reduced.
  • FIG. 12C shows an enlarged view of a region where the oxide semiconductor film 155b having conductivity is in contact with the conductive film 159.
  • the coating film 156 including X in the Cu-X alloy film is formed at an interface between the oxide semiconductor film 155b having conductivity and the conductive film 159a in some cases.
  • the coating film 156 serving as a blocking film against Cu entry of Cu in the Cu-X alloy film into the oxide semiconductor film 155b having conductivity can be suppressed.
  • a coating film such as the coating film 156a is formed on the periphery of the conductive films 159 in some cases, similarly to the case of the conductive film 159 in Embodiment 1.
  • a single layer of the conductive film 159a formed of the Cu-X alloy film can be formed over the oxide semiconductor film 155b having conductivity.
  • the conductive film 159 can have a three-layer structure.
  • the conductive film 159 has a stacked-layer structure of the conductive film 159a in contact with the oxide semiconductor film 155b having conductivity, the conductive film 159b in contact with the conductive film 159a, and the conductive film 159c in contact with the conductive film 159b.
  • the conductive film 159c formed of the Cu-X alloy film When the conductive film 159c formed of the Cu-X alloy film is provided over the conductive film 159b formed of the conductive film including a low-resistance material in the conductive film 159, the conductive film 159c formed of the Cu-X alloy film serves as a protective film of the conductive film 159b including a low-resistance material; thus, the reaction of the conductive film 159b including a low-resistance material in the formation of the insulating film 157 can be prevented.
  • a coating film such as the coating films 156b and 156c is formed on the periphery of the conductive film 159 in some cases, similarly to the case of the conductive film 159 in Embodiment 1.
  • a capacitor 180e in FIG. 14A includes the conductive film 159a formed of the single-layer Cu-X alloy film between the insulating film 153 and the oxide semiconductor film 155b having conductivity.
  • the conductive film 159 is provided between the insulating film 153 and the oxide semiconductor film 155b having conductivity and has a two-layer structure.
  • the conductive film 159 is formed by stacking the conductive film 159a formed of the Cu-X alloy film and the conductive film 159b formed of the conductive film including a low-resistance material.
  • the conductive film 159 is provided between the insulating film 153 and the oxide semiconductor film 155b having conductivity and has a three-layer structure.
  • the conductive film 159 is formed by stacking the conductive film 159a formed of the Cu-X alloy film, the conductive film 159b formed of the conductive film including a low-resistance material, and the conductive film 159c formed of the Cu-X alloy film.
  • the conductive film 159c formed of the Cu-X alloy film When the conductive film 159c formed of the Cu-X alloy film is provided over the conductive film 159b formed of the conductive film including a low-resistance material in the conductive film 159, the conductive film 159c formed of the Cu-X alloy film serves as a protective film of the conductive film 159b including a low-resistance material; thus, the reaction of the conductive film 159b including a low-resistance material in the formation of the oxide semiconductor film 155b having conductivity and the insulating film 157 can be prevented. [0176]
  • a coating film such as the coating films 156, 156a, 156b and 156c is formed on the periphery of the conductive film 159 in some cases, similarly to the case of the conductive film 159 in Embodiment 1.
  • FIGS. 15A to 15C A semiconductor device provided with a capacitor including the oxide semiconductor film having conductivity in Embodiment 1 is described with reference to FIGS. 15A to 15C, FIG. 16, FIG. 17, FIGS. 18A to 18D, FIGS. 19A to 19C, FIGS. 20A to 20C, FIGS. 21 A and 21B, FIG. 22, FIG. 23, FIG. 24, FIG. 25, and FIGS. 26A and 26B.
  • FIG. 15A illustrates an example of a display device.
  • a display device illustrated in FIG. 15A includes a pixel portion 101; a scan line driver circuit 104; a signal line driver circuit 106; m scan lines 107 which are arranged parallel or substantially parallel to each other and whose potentials are controlled by the scan line driver circuit 104; and n signal lines 109 which are arranged parallel or substantially parallel to each other and whose potentials are controlled by the signal line driver circuit 106.
  • the pixel portion 101 further includes a plurality of pixels 103 arranged in a matrix.
  • capacitor lines 115 arranged parallel or substantially parallel may be provided along the signal lines 109. Note that the capacitor lines 115 may be arranged parallel or substantially parallel along the scan lines 107.
  • the scan line driver circuit 104 and the signal line driver circuit 106 are collectively referred to as a driver circuit portion in some cases.
  • the display device also includes a driver circuit for driving a plurality of pixels, and the like.
  • the display device may also be referred to as a liquid crystal module including a control circuit, a power supply circuit, a signal generation circuit, a backlight module, and the like provided over another substrate.
  • Each scan line 107 is electrically connected to the n pixels 103 in the corresponding row among the pixels 103 arranged in m rows and n columns in the pixel portion 101.
  • Each signal line 109 is electrically connected to the m pixels 103 in the corresponding column among the pixels 103 arranged in m rows and n columns.
  • m and n are each an integer of 1 or more.
  • Each capacitor line 115 is electrically connected to the m pixels 103 in the corresponding columns among the pixels 103 arranged in m rows and n columns. Note that in the case where the capacitor lines 115 are arranged parallel or substantially parallel along the scan lines 107, each capacitor line 115 is electrically connected to the n pixels 103 in the corresponding rows among the pixels 103 arranged in m rows and n columns.
  • the capacitor line is not provided and a common line or a common electrode serves as a capacitor line.
  • a pixel refers to a region surrounded by scan lines and signal lines and exhibiting one color. Therefore, in the case of a color display device having color elements of R (red), G (green), and B (blue), a minimum unit of an image is composed of three pixels of an R pixel, a G pixel, and a B pixel. Note that color reproducibility can be improved by adding a yellow pixel, a cyan pixel, a magenta pixel, or the like to the R pixel, the G pixel, and the B pixel. Moreover, power consumption of the display device can be reduced by adding a W (white) pixel to the R pixel, the G pixel, and the B pixel.
  • brightness of the liquid crystal display device can be improved by adding a W pixel to each of the R pixel, the G pixel, and the B pixel. As a result, the power consumption of the liquid crystal display device can be reduced.
  • FIGS. 15B and 15C illustrate examples of a circuit configuration that can be used for the pixels 103 in the display device illustrated in FIG. 15 A.
  • the pixel 103 in FIG. 15B includes a liquid crystal element 121, a transistor 102, and a capacitor 105.
  • the potential of one of a pair of electrodes of the liquid crystal element 121 is set as appropriate according to the specifications of the pixel 103.
  • the alignment state of the liquid crystal element 121 depends on written data.
  • a common potential may be supplied to one of the pair of electrodes of the liquid crystal element 121 included in each of a plurality of pixels 103.
  • the potential supplied to the one of the pair of electrodes of the liquid crystal element 121 in the pixel 103 in one row may be different from the potential supplied to the one of the pair of electrodes of the liquid crystal element 121 in the pixel 103 in another row.
  • the liquid crystal element 121 is an element that controls transmission or non-transmission of light utilizing an optical modulation action of liquid crystal. Note that the optical modulation action of the liquid crystal is controlled by an electric field applied to the liquid crystal (including a horizontal electric field, a vertical electric field, and a diagonal electric field).
  • Examples of the liquid crystal element 121 are a nematic liquid crystal, a cholesteric liquid crystal, a smectic liquid crystal, a thermotropic liquid crystal, a lyotropic liquid crystal, a ferroelectric liquid crystal, and an anti -ferroelectric liquid crystal.
  • any of the following modes can be given: a TN mode, a VA mode, an ASM (axially symmetric aligned micro-cell) mode, an OCB (optically compensated birefringence) mode, an MVA mode, a PVA (patterned vertical alignment) mode, an IPS mode, an FFS mode, a TBA (transverse bend alignment) mode, and the like.
  • a TN mode a TN mode
  • VA mode axially symmetric aligned micro-cell
  • an OCB optical compensated birefringence
  • MVA mode axially symmetric aligned micro-cell
  • PVA patterned vertical alignment
  • IPS mode patterned vertical alignment
  • FFS mode FFS mode
  • TBA transverse bend alignment
  • the liquid crystal element may be formed using a liquid crystal composition including liquid crystal exhibiting a blue phase and a chiral material.
  • the liquid crystal exhibiting a blue phase has a short response time of 1 msec or less and is optically isotropic; therefore, alignment treatment is not necessary and viewing angle dependence is small.
  • one of a source electrode and a drain electrode of the transistor 102 is electrically connected to the signal line 109, and the other is electrically connected to the other of the pair of electrodes of the liquid crystal element 121.
  • a gate electrode of the transistor 102 is electrically connected to the scan line 107.
  • the transistor 102 has a function of controlling whether to write a data signal by being turned on or off.
  • one of a pair of electrodes of the capacitor 105 is electrically connected to the capacitor line 115 to which a potential is supplied, and the other thereof is electrically connected to the other of the pair of electrodes of the liquid crystal element 121.
  • the potential of the capacitor line 115 is set as appropriate in accordance with the specifications of the pixel 103.
  • the capacitor 105 functions as a storage capacitor for storing written data.
  • the pixel 103 in FIG. 15C includes a transistor 133 performing switching of a display element, the transistor 102 controlling pixel driving, a transistor 135, the capacitor 105, and a light-emitting element 131.
  • One of a source electrode and a drain electrode of the transistor 133 is electrically connected to the signal line 109 to which a data signal is supplied.
  • a gate electrode of the transistor 133 is electrically connected to a scan line 107 to which a gate signal is supplied.
  • the transistor 133 has a function of controlling whether to write a data signal by being turned on or off.
  • One of a source electrode and a drain electrode of the transistor 102 is electrically connected to a wiring 137 serving as an anode line, and the other is electrically connected to one electrode of the light-emitting element 131.
  • the gate electrode of the transistor 102 is electrically connected to the other of the source electrode and the drain electrode of the transistor 133 and one electrode of the capacitor 105.
  • the transistor 102 has a function of controlling current flowing through the light-emitting element 131 by being turned on or off.
  • One of a source electrode and a drain electrode of the transistor 135 is connected to a wiring 139 to which a reference potential of data is supplied, and the other thereof is electrically connected to the one electrode of the light-emitting element 131 and the other electrode of the capacitor 105. Moreover, a gate electrode of the transistor 135 is electrically connected to the scan line 107 to which the gate signal is supplied.
  • the transistor 135 has a function of adjusting the current flowing through the light-emitting element 131. For example, when the internal resistance of the light-emitting element 131 increases because of deterioration or the like of the light-emitting element 131, the current flowing through the light-emitting element 131 can be corrected by monitoring current flowing through the wiring 139 to which the one of the source electrode and the drain electrode of the transistor 135 is connected.
  • the potential supplied to the wiring 139 can be set to 0 V, for example.
  • the one electrode of the capacitor 105 is electrically connected to the gate electrode of the transistor 102 and the other of the source electrode and the drain electrode of the transistor 133, and the other electrode of the capacitor 105 is electrically connected to the other of the source electrode and the drain electrode of the transistor 135 and the one electrode of the light-emitting element 131.
  • the capacitor 105 functions as a storage capacitor for storing written data.
  • the one electrode of the light-emitting element 131 is electrically connected to the other of the source electrode and the drain electrode of the transistor 135, the other electrode of the capacitor 105, and the other of the source electrode and the drain electrode of the transistor 102. Furthermore, the other electrode of the light-emitting element 131 is electrically connected to a wiring 141 serving as a cathode.
  • an organic electroluminescent element also referred to as an organic EL element
  • the light-emitting element 131 is not limited to an organic EL element; an inorganic EL element including an inorganic material may be used.
  • a high power supply potential VDD is supplied to one of the wiring 137 and the wiring 141, and a low power supply potential VSS is supplied to the other.
  • the high power supply potential VDD is supplied to the wiring 137, and the low power supply potential VSS is supplied to the wiring 141.
  • FIGS. 15B and 15C each illustrate an example where the liquid crystal element 121 and the light-emitting element 131 are used as a display element, one embodiment of the present invention is not limited thereto. Any of a variety of display elements can be used.
  • Examples of a display element include a display medium whose contrast, luminance, reflectance, transmittance, or the like is changed by electromagnetic action, such as an LED (e.g., a white LED, a red LED, a green LED, or a blue LED), a transistor (a transistor that emits light depending on current), an electron emitter, electronic ink, an electrophoretic element, a grating light valve (GLV), a plasma display panel (PDP), a display element using micro electro mechanical system (MEMS), a digital micromirror device (DMD), a digital micro shutter (DMS), an interferometric modulator display (FMOD) element, a MEMS shutter display element, an optical-interference-type MEMS display element, an electrowetting element, a piezoelectric ceramic display, or a carbon nanotube.
  • an LED e.g., a white LED, a red LED, a green LED, or a blue LED
  • a transistor a transistor that emits light depending on current
  • examples of display devices including EL elements include an EL display.
  • Examples of display devices including electron emitters are a field emission display (FED) and an SED-type flat panel display (SED: surface-conduction electron-emitter display).
  • Examples of display devices including liquid crystal elements include a liquid crystal display (e.g., a transmissive liquid crystal display, a transflective liquid crystal display, a reflective liquid crystal display, a direct- view liquid crystal display, or a projection liquid crystal display) and the like.
  • An example of a display device including electronic ink or electrophoretic elements is electronic paper.
  • some of or all of pixel electrodes function as reflective electrodes.
  • some or all of pixel electrodes are formed to contain aluminum, silver, or the like.
  • a memory circuit such as an SRAM can be provided under the reflective electrodes, leading to lower power consumption.
  • FIG. 16 is a top view of the pixel 103 shown in FIG. 15B.
  • FIG. 16 is a top view of a plurality of pixels 103a, 103b, and 103c included in the liquid crystal display device.
  • a conductive film 13 functioning as a scan line extends in a direction substantially perpendicularly to a conductive film functioning as a signal line (in the lateral direction in the drawing).
  • the conductive film 21a functioning as a signal line extends in a direction substantially perpendicularly to the conductive film functioning as a scan line (in the vertical direction in the drawing).
  • the conductive film 13 functioning as a scan line is electrically connected to the scan line driver circuit 104 (see FIG. 15 A), and the conductive film 21a functioning as a signal line is electrically connected to the signal line driver circuit 106 (see FIG. 15 A).
  • the transistor 102 is provided in a region where the conductive film functioning as a scan line and the conductive film functioning as a signal line intersect with each other.
  • the transistor 102 includes the conductive film 13 functioning as a gate electrode; a gate insulating film (not illustrated in FIG. 16); the oxide semiconductor film 19a where a channel region is formed, over the gate insulating film; and the conductive film 21a and a conductive film 21b functioning as a source electrode and a drain electrode.
  • the conductive film 13 also functions as a conductive film functioning as a scan line, and a region of the conductive film 13 that overlaps with the oxide semiconductor film 19a serves as the gate electrode of the transistor 102.
  • the conductive film 21a also functions as a conductive film functioning as a signal line, and a region of the conductive film 21a that overlaps with the oxide semiconductor film 19a functions as the source electrode or the drain electrode of the transistor 102. Furthermore, in the top view of FIG. 16, an end portion of the conductive film functioning as a scan line is positioned on an outer side of an end portion of the oxide semiconductor film 19a. Thus, the conductive film functioning as a scan line functions as a light-blocking film for blocking light from a light source such as a backlight. For this reason, the oxide semiconductor film 19a included in the transistor is not irradiated with light, so that a variation in the electrical characteristics of the transistor can be suppressed.
  • the transistor 102 includes the organic insulating film 31 overlapping with the oxide semiconductor film 19a.
  • the organic insulating film 31 overlaps with the oxide semiconductor film 19a (in particular, a region of the oxide semiconductor film 19a which is between the conductive films 21a and 21b) with an inorganic insulating film (not illustrated in FIG. 16) provided therebetween.
  • the conductive film 21b is electrically connected to an oxide semiconductor film 19b having conductivity.
  • a common electrode 29 is provided over the oxide semiconductor film 19b having conductivity with an insulating film provided therebetween.
  • An opening 40 indicated by a dashed-dotted line is provided in the insulating film provided over the oxide semiconductor film 19b having conductivity.
  • the oxide semiconductor film 19b having conductivity is in contact with a nitride insulating film (not illustrated in FIG. 16) in the opening 40.
  • the common electrode 29 includes stripe regions extending in a direction intersecting with the conductive film 21a functioning as a signal line.
  • the stripe regions are connected to a region extending in a direction parallel or substantially parallel to the conductive film 21a functioning as a signal line. Accordingly, the stripe regions of the common electrode 29 are at the same potential in pixels.
  • the capacitor 105 is formed in a region where the oxide semiconductor film 19b having conductivity and the common electrode 29 overlap with each other.
  • the oxide semiconductor film 19b having conductivity and the common electrode 29 each have a light-transmitting property. That is, the capacitor 105 has a light-transmitting property.
  • an FFS mode liquid crystal display device is provided with the common electrode including the stripe regions extending in a direction intersecting with the conductive film functioning as a signal line.
  • the display device can have excellent contrast.
  • the capacitor 105 can be formed large (in a large area) in the pixel 103.
  • a display device with a large-capacitance capacitor as well as an aperture ratio increased to typically 50 % or more, preferably 60 % or more can be provided.
  • the area of a pixel is small and accordingly the area of a capacitor is also small. For this reason, the amount of charges accumulated in the capacitor is small in the high-resolution display device.
  • the capacitor 105 of this embodiment has a light-transmitting property, when the capacitor 105 is provided in a pixel, a sufficient capacitance value can be obtained in the pixel and the aperture ratio can be improved.
  • the capacitor 105 can be favorably used for a high-resolution display device with a pixel density of 200 pixels per inch (ppi) or more, 300 ppi or more, or furthermore, 500 ppi or more.
  • a period during which the alignment of liquid crystal molecules of a liquid crystal element can be kept constant in the state where an electric field is applied can be made longer.
  • the period can be made longer in a display device which displays a still image, the number of times of rewriting image data can be reduced, leading to a reduction in power consumption.
  • the aperture ratio can be improved even in a high-resolution display device, which makes it possible to use light from a light source such as a backlight efficiently, so that power consumption of the display device can be reduced.
  • FIG. 17 is a cross-sectional view taken along dashed-dotted lines A-B and C-D in FIG. 16.
  • the transistor 102 illustrated in FIG. 17 is a channel-etched transistor. Note that the transistor 102 in the channel length direction and the capacitor 105 are illustrated in the cross-sectional view taken along dashed-dotted line A-B, and the transistor 102 in the channel width direction is illustrated in the cross-sectional view taken along dashed-dotted line C-D.
  • the liquid crystal display device described in this embodiment includes a pair of substrates (a first substrate 11 and a second substrate 342), an element layer in contact with the first substrate 11, an element layer in contact with the second substrate 342, and a liquid crystal layer 320 provided between the element layers.
  • the element layer is a generic term used to refer to layers interposed between the substrate and the liquid crystal layer.
  • the substrate and the element layer are collectively referred to as an element substrate in some cases.
  • a liquid crystal element 322 is provided between a pair of substrates (the first substrate 11 and the second substrate 342).
  • the liquid crystal element 322 includes the oxide semiconductor film 19b having conductivity over the first substrate 11, the common electrode 29, a nitride insulating film 27, a film controlling alignment (hereinafter referred to as an alignment film 33), and the liquid crystal layer 320.
  • the oxide semiconductor film 19b having conductivity functions as one electrode (also referred to as a pixel electrode) of the liquid crystal element 322, and the common electrode 29 functions as the other electrode of the liquid crystal element 322.
  • the transistor 102 in FIG. 17 has a single-gate structure and includes the conductive film 13 functioning as a gate electrode over the first substrate 11.
  • the transistor 102 includes a nitride insulating film 15 formed over the first substrate 11 and the conductive film 13 functioning as a gate electrode, an oxide insulating film 17 formed over the nitride insulating film 15, the oxide semiconductor film 19a overlapping with the conductive film 13 functioning as a gate electrode with the nitride insulating film 15 and the oxide insulating film 17 provided therebetween, and the conductive films 21a and 21b functioning as a source electrode and a drain electrode which are in contact with the oxide semiconductor film 19a.
  • the nitride insulating film 15 and the oxide insulating film 17 function as the gate insulating film 14. Moreover, an oxide insulating film 23 is formed over the oxide insulating film 17, the oxide semiconductor film 19a, and the conductive films 21a and 21b functioning as a source electrode and a drain electrode, and an oxide insulating film 25 is formed over the oxide insulating film 23.
  • the nitride insulating film 27 is formed over the oxide insulating film 23, the oxide insulating film 25, and the conductive film 21b.
  • the oxide insulating film 23, the oxide insulating film 25, and the nitride insulating film 27 function as the inorganic insulating film 30.
  • the oxide semiconductor film 19b having conductivity is formed over the oxide insulating film 17.
  • the oxide semiconductor film 19b having conductivity is connected to one of the conductive films 21a and 21b functioning as a source electrode and a drain electrode, here, connected to the conductive film 21b.
  • the common electrode 29 is formed over the nitride insulating film 27.
  • the organic insulating film 31 overlapping with the oxide semiconductor film 19a of the transistor 102 with the inorganic insulating film 30 provided therebetween is included.
  • the substrate 151 described in Embodiment 1 can be used as appropriate.
  • the conductive film 13 functioning as a gate electrode can be formed using a metal element selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, and tungsten; an alloy containing any of these metal elements as a component; an alloy containing any of these metal elements in combination; or the like. Furthermore, one or more metal elements selected from manganese and zirconium may be used.
  • the conductive film 13 functioning as a gate electrode may have a single-layer structure or a stacked-layer structure of two or more layers.
  • a single-layer structure of an aluminum film containing silicon, a two-layer structure in which an aluminum film is stacked over a titanium film, a two-layer structure in which a titanium film is stacked over a titanium nitride film, a two-layer structure in which a tungsten film is stacked over a titanium nitride film, a two-layer structure in which a tungsten film is stacked over a tantalum nitride film or a tungsten nitride film, a two-layer structure in which a copper film is stacked over a titanium film, a two-layer structure in which a copper film is stacked over a molybdenum film, and a three-layer structure in which a titanium film, an aluminum film, and a titanium film are stacked in this order can be given.
  • the structure and the material used for the conductive film 159 in Embodiment 1 can be used as appropriate.
  • the light-transmitting conductive film described in the description of the conductive film 181 in Embodiment 3 can be used.
  • the conductive film 13 serving as a gate electrode can have a stacked-layer structure of the light-transmitting conductive film and the metal element.
  • the conductive film 13 serving as a gate electrode may be formed using the oxide semiconductor film 155b having conductivity in Embodiment 1.
  • the nitride insulating film 15 can be a nitride insulating film that is hardly permeated by oxygen. Furthermore, a nitride insulating film which is hardly permeated by oxygen, hydrogen, and water can be used. As the nitride insulating film that is hardly permeated by oxygen and the nitride insulating film that is hardly permeated by oxygen, hydrogen, and water, a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, an aluminum nitride oxide film, or the like is given.
  • an oxide insulating film such as an aluminum oxide film, an aluminum oxynitride film, a gallium oxide film, a gallium oxynitride film, an yttrium oxide film, an yttrium oxynitride film, a hafnium oxide film, or a hafnium oxynitride film can be used.
  • the thickness of the nitride insulating film 15 is preferably greater than or equal to 5 nm and less than or equal to 100 nm, further preferably greater than or equal to 20 nm and less than or equal to 80 nm.
  • the oxide insulating film 17 may be formed to have a single-layer structure or a stacked-layer structure using, for example, one or more of a silicon oxide film, a silicon oxynitride film, a silicon nitride oxide film, a silicon nitride film, an aluminum oxide film, a hafnium oxide film, a gallium oxide film, and a Ga-Zn-based metal oxide film.
  • the oxide insulating film 17 may also be formed using a material having a high relative dielectric constant such as hafnium silicate (HfSiO x ), hafnium silicate to which nitrogen is added (HfSi x OyN z ), hafnium aluminate to which nitrogen is added (HfAl x OyN z ), hafnium oxide, or yttrium oxide, so that gate leakage current of the transistor can be reduced.
  • hafnium silicate hafnium silicate to which nitrogen is added
  • HfAl x OyN z hafnium aluminate to which nitrogen is added
  • hafnium oxide or yttrium oxide
  • the thickness of the oxide insulating film 17 is preferably greater than or equal to 5 nm and less than or equal to 400 nm, further preferably greater than or equal to 10 nm and less than or equal to 300 nm, still further preferably greater than or equal to 50 nm and less than or equal to 250 nm.
  • the oxide semiconductor film 19a and the oxide semiconductor film 19b having conductivity are formed at the same time and are formed using a metal oxide film such as an In-Ga oxide film, an In-Zn oxide film, or an In-M-Zn oxide film ( represents Al, Ga, Y, Zr, Sn, La, Ce, or Nd).
  • a metal oxide film such as an In-Ga oxide film, an In-Zn oxide film, or an In-M-Zn oxide film ( represents Al, Ga, Y, Zr, Sn, La, Ce, or Nd.
  • the oxide semiconductor film 19a and the oxide semiconductor film 19b having conductivity include the same metal element.
  • the oxide semiconductor film 19b having conductivity has different electrical characteristics from the oxide semiconductor film 19a. Specifically, the oxide semiconductor film 19a has semiconductor characteristics and the oxide semiconductor film 19b having conductivity has conductivity.
  • the thicknesses of the oxide semiconductor film 19a and the oxide semiconductor film 19b having conductivity are greater than or equal to 3 nm and less than or equal to 200 nm, preferably greater than or equal to 3 nm and less than or equal to 100 nm, further preferably greater than or equal to 3 nm and less than or equal to 50 nm.
  • the energy gap of the oxide semiconductor film 19a is 2 eV or more, preferably 2.5 eV or more, further preferably 3 eV or more.
  • the off-state current of the transistor 102 can be reduced by using an oxide semiconductor having such a wide energy gap.
  • An oxide semiconductor film with low carrier density is used as the oxide semiconductor film 19a.
  • an oxide semiconductor film whose carrier density is 1 17 /cm 3 or lower, preferably 1 15 /cm3 or lower, preferably 1 13 x 10 x 10 x 10 /cm or lower, preferably 8 x 10 /cm or lower, preferably 1 x 10 /cm or lower, further preferably lower than 1 x 10 10 /cm 3 , and is 1 x 10 ⁇ 9 /cm 3 or higher is used as the oxide semiconductor film 19a.
  • a material with an appropriate composition may be used depending on required semiconductor characteristics and electrical characteristics (e.g., field-effect mobility and threshold voltage) of a transistor. Furthermore, in order to obtain required semiconductor characteristics of a transistor, it is preferable that the carrier density, the impurity concentration, the defect density, the atomic ratio of a metal element to oxygen, the interatomic distance, the density, and the like of the oxide semiconductor film 19a be set to be appropriate.
  • the oxide semiconductor film 19a by using an oxide semiconductor film in which the impurity concentration is low and density of defect states is low as the oxide semiconductor film 19a, in which case a transistor which has more excellent electrical characteristics can be manufactured.
  • the state in which impurity concentration is low and density of defect states is low (the amount of oxygen vacancies is small) is referred to as "highly purified intrinsic” or “substantially highly purified intrinsic”.
  • a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor has few carrier generation sources, and thus has a low carrier density in some cases.
  • a transistor in which a channel region is formed in the oxide semiconductor film rarely has a negative threshold voltage (is rarely normally on).
  • a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low density of defect states and accordingly has few carrier traps in some cases. Furthermore, the highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has an extremely low off-state current; even when an element has a channel width of 1 x 10 6 ⁇ and a channel length (L) of 10 ⁇ , the off-state current can be less than or equal to the measurement limit of a semiconductor parameter analyzer, i.e., less than or equal to 1 x 10 "13 A, at a voltage (drain voltage) between a source electrode and a drain electrode of from 1 V to 10 V. Thus, the transistor in which a channel region is formed in the oxide semiconductor film has a small variation in electrical characteristics and high reliability in some cases.
  • the impurities hydrogen, nitrogen, alkali metal, and alkaline earth metal are given.
  • Hydrogen contained in the oxide semiconductor film reacts with oxygen bonded to a metal atom to be water, and in addition, an oxygen vacancy is formed in a lattice from which oxygen is released (or a portion from which oxygen is released). Due to entry of hydrogen into the oxygen vacancy, an electron serving as a carrier is generated in some cases. Furthermore, in some cases, bonding of part of hydrogen to oxygen bonded to a metal atom causes generation of an electron serving as a carrier. Thus, a transistor including an oxide semiconductor which contains hydrogen is likely to be normally on.
  • the hydrogen concentration which is measured by secondary ion mass spectrometry is set to be lower than or equal to 5 x 10 19 atoms/cm 3 , preferably lower than or equal to 1 x 10 19 atoms/cm 3 , further preferably lower than or equal to 5 x 10 18 atoms/cm 3 , still further preferably lower than or equal to 1 x 10 18 atoms/cm 3 , yet still further preferably lower than or equal to 5 x 10 17 atoms/cm 3 , yet still furthermore preferably lower than or equal to 1 x 10 16 atoms/cm 3 .
  • SIMS secondary ion mass spectrometry
  • the concentration of silicon or carbon (the concentration is measured by SIMS) of the oxide semiconductor film 19a is set to be lower than or equal to 2 x 10 18 atoms/cm 3 , preferably lower than or equal to 2 x 10 17 atoms/cm 3 .
  • the concentration of alkali metal or alkaline earth metal in the oxide semiconductor film 19a which is measured by SIMS, is set to be lower than or equal to 1 x 10 atoms/cm , preferably lower than or equal to 2 x 10 atoms/cm .
  • Alkali metal and alkaline earth metal might generate carriers when bonded to an oxide semiconductor, in which case the off-state current of the transistor might be increased. Therefore, it is preferable to reduce the concentration of alkali metal or alkaline earth metal in the oxide semiconductor film 19a.
  • the oxide semiconductor film 19a when containing nitrogen, the oxide semiconductor film 19a easily has n-type conductivity by generation of electrons serving as carriers and an increase of carrier density. Thus, a transistor including an oxide semiconductor which contains nitrogen is likely to be normally on. For this reason, nitrogen in the oxide semiconductor film is preferably reduced as much as possible; the nitrogen concentration which is measured by SEVIS is preferably set to be, for example, lower than or equal to 5 x 10 18 atoms/cm 3 .
  • the oxide semiconductor film 19b having conductivity is formed by including defects, e.g., oxygen vacancies, and impurities in an oxide semiconductor film formed at the same time as the oxide semiconductor film 19a.
  • the oxide semiconductor film 19b having conductivity serves as an electrode, e.g., a pixel electrode in this embodiment.
  • the oxide semiconductor film 19a and the oxide semiconductor film 19b having conductivity are both formed over the oxide insulating film 17, but differ in impurity concentration. Specifically, the oxide semiconductor film 19b having conductivity has a higher impurity concentration than the oxide semiconductor film 19a.
  • the hydrogen concentration in the oxide semiconductor film 19a is lower than or equal to 5 x 10 19 atoms/cm 3 , preferably lower than or equal to 1 x 10 19 atoms/cm 3 , further preferably lower than or equal to 5 x 10 18 atoms/cm 3 , still further preferably lower than or equal to 1 x 10 18 atoms/cm 3 , yet further preferably lower than or equal to 5 x 10 17 atoms/cm 3 , yet furthermore preferably lower than or equal to 1 x 10 16 atoms/cm 3 .
  • the hydrogen concentration in the oxide semiconductor film 19b having conductivity is higher than or equal to 8 x 10 19 atoms/cm , preferably higher than or equal to 1 x 10 atoms/cm , further preferably higher than or equal to 5 x 10 20 atoms/cm 3 .
  • the hydrogen concentration in the oxide semiconductor film 19b having conductivity is greater than or equal to 2 times, preferably greater than or equal to 10 times that in the oxide semiconductor film 19a.
  • the oxide semiconductor film 19b having conductivity has lower resistivity than the oxide semiconductor film 19a.
  • the resistivity of the oxide semiconductor film 19b having conductivity is preferably higher than or equal to 1 x 10 "8 times and lower than 1 x 10 "1 times the resistivity of the oxide semiconductor film 19a.
  • the resistivity of the oxide semiconductor film 19b having conductivity is typically higher than or equal to 1 x 10 "3 Qcm and lower than 1 x 10 4 Qcm, preferably higher than or equal to 1 x 10 "3 Qcm and lower than 1 x 10 "1 Qcm.
  • the oxide semiconductor film 19a and the oxide semiconductor film 19b having conductivity can each have a crystal structure similar to that of the oxide semiconductor film 155b having conductivity in Embodiment 1, as appropriate.
  • the structure and the material used for the conductive film 159 in Embodiment 1 can be used as appropriate.
  • the conductive film 21a has a stacked-layer structure of a conductive film 21a_l and a conductive film 21a_2.
  • the conductive film 21b has a stacked-layer structure of a conductive film 21b_l and a conductive film 21b_2.
  • a Cu-X alloy film is used as the conductive films 21a_l and 21b_l.
  • a conductive film including a low-resistance material is used as the conductive films 21a_2 and 21b_2.
  • an oxide insulating film which contains more oxygen than that in the stoichiometric composition is preferably used.
  • an oxide insulating film which permeates oxygen is formed, and as the oxide insulating film 25, an oxide insulating film which contains more oxygen than that in the stoichiometric composition is formed.
  • the oxide insulating film 23 is an oxide insulating film through which oxygen is permeated. Thus, oxygen released from the oxide insulating film 25 provided over the oxide insulating film 23 can be moved to the oxide semiconductor film 19a through the oxide insulating film 23. Moreover, the oxide insulating film 23 also serves as a film which relieves damage to the oxide semiconductor film 19a at the time of forming the oxide insulating film 25 later.
  • the oxide insulating film 23 is preferably an oxide insulating film containing nitrogen and having a small number of defects.
  • oxide insulating film containing nitrogen and having a small number of defects include a silicon oxynitride film and an aluminum oxynitride film.
  • a first signal that appears at a g-factor of greater than or equal to 2.037 and less than or equal to 2.039, a second signal that appears at a g-factor of greater than or equal to 2.001 and less than or equal to 2.003, and a third signal that appears at a g-factor of greater than or equal to 1.964 and less than or equal to 1.966 are observed.
  • the split width of the first and second signals and the split width of the second and third signals that are obtained by ESR measurement using an X-band are each approximately 5 ml
  • the sum of the spin densities of the first signal that appears at a ⁇ --factor of greater than or equal to 2.037 and less than or equal to 2.039, the second signal that appears at a g-factor of greater than or equal to 2.001 and less than or equal to 2.003, and the third signal that appears at a g-factor of greater than or equal to 1.964 and less than or equal to 1.966 is lower than 1 x 10 18 spins/cm 3 , typically higher than or equal to 1 x 10 17 spins/cm 3 and lower than 1 x 10 18 spins/cm 3 .
  • the first signal that appears at a ⁇ -factor of greater than or equal to 2.037 and less than or equal to 2.039, the second signal that appears at a ⁇ -factor of greater than or equal to 2.001 and less than or equal to 2.003, and the third signal that appears at a ⁇ -factor of greater than or equal to 1.964 and less than or equal to 1.966 correspond to signals attributed to nitrogen oxide (NO x ; x is greater than or equal to 0 and less than or equal to 2, preferably greater than or equal to 1 and less than or equal to 2).
  • nitrogen oxide include nitrogen monoxide and nitrogen dioxide.
  • the lower the total spin density of the first signal that appears at a ⁇ -factor of greater than or equal to 2.037 and less than or equal to 2.039, the second signal that appears at a ⁇ -factor of greater than or equal to 2.001 and less than or equal to 2.003, and the third signal that appears at a ⁇ -factor of greater than or equal to 1.964 and less than or equal to 1.966 is, the lower the content of nitrogen oxide in the oxide insulating film is.
  • the oxide insulating film 23 contains a small amount of nitrogen oxide as described above, the carrier trap at the interface between the oxide insulating film 23 and the oxide semiconductor film can be reduced.
  • the amount of change in the threshold voltage of the transistor included in the semiconductor device can be reduced, which leads to a reduced change in the electrical characteristics of the transistor.
  • the oxide insulating film 23 preferably has a nitrogen concentration measured by secondary ion mass spectrometry (SIMS) of lower than or equal to 6 x 10 20 atoms/cm 3 .
  • SIMS secondary ion mass spectrometry
  • nitrogen oxide is unlikely to be generated in the oxide insulating film 23, so that the carrier trap at the interface between the oxide insulating film 23 and the oxide semiconductor film 19a can be reduced.
  • the amount of change in the threshold voltage of the transistor included in the semiconductor device can be reduced, which leads to a reduced change in the electrical characteristics of the transistor.
  • the nitride oxide and ammonia react with each other in heat treatment in the manufacturing process; accordingly, the nitride oxide is released as a nitrogen gas.
  • the nitrogen concentration of the oxide insulating film 23 and the amount of nitrogen oxide therein can be reduced.
  • the carrier trap at the interface between the oxide insulating film 23 and the oxide semiconductor film 19a can be reduced.
  • the amount of change in threshold voltage of the transistor included in the semiconductor device can be reduced, which leads to a reduced change in the electrical characteristics of the transistor.
  • oxygen released from the oxide insulating film 25 provided over the oxide insulating film 23 can be moved to the oxide semiconductor film 19a through the oxide insulating film 23.
  • the oxide insulating film 25 is formed in contact with the oxide insulating film
  • the oxide insulating film 25 is formed using an oxide insulating film which contains oxygen at a higher proportion than the stoichiometric composition. Part of oxygen is released by heating from the oxide insulating film which contains oxygen at a higher proportion than the stoichiometric composition.
  • the oxide insulating film which contains oxygen at a higher proportion than the stoichiometric composition is an oxide insulating film of which the amount of released oxygen converted into oxygen atoms is greater than or equal to 1.0 x 10 18 atoms/cm 3 , preferably greater than or equal to 3.0 x 10 atoms/cm in TDS analysis. Note that the surface temperature of the oxide insulating film 25 in the TDS analysis is preferably higher than or equal to 100 °C and lower than or equal to 700 °C, or higher than or equal to 100 °C and lower than or equal to 500 °C.
  • the oxide insulating film 25 is provided more apart from the oxide semiconductor film 19a than the oxide insulating film 23 is; thus, the oxide insulating film 25 may have higher defect density than the oxide insulating film 23.
  • the nitride insulating film 27 can be a nitride insulating film which is hardly permeated by oxygen. Furthermore, a nitride insulating film which is hardly permeated by oxygen, hydrogen, and water can be used.
  • the nitride insulating film 27 is formed using a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, an aluminum nitride oxide film, or the like with a thickness greater than or equal to 50 nm and less than or equal to 300 nm, preferably greater than or equal to 100 nm and less than or equal to 200 nm.
  • the oxide insulating film which contains oxygen at a higher proportion than the stoichiometric composition is included in the oxide insulating film 23 or the oxide insulating film 25, part of oxygen contained in the oxide insulating film 23 or the oxide insulating film 25 can be moved to the oxide semiconductor film 19a, so that the amount of oxygen vacancies contained in the oxide semiconductor film 19a can be reduced.
  • the threshold voltage of a transistor using an oxide semiconductor film with oxygen vacancies shifts negatively with ease, and such a transistor tends to be normally on. This is because charges are generated owing to oxygen vacancies in the oxide semiconductor film and the resistance is thus reduced.
  • the transistor having normally-on characteristic causes various problems in that malfunction is likely to be caused when in operation and that power consumption is increased when not in operation, for example. Furthermore, there is a problem in that the amount of change in electrical characteristics, typically in threshold voltage, of the transistor is increased by change over time or due to a stress test.
  • the oxide insulating film 23 or the oxide insulating film 25 provided over the oxide semiconductor film 19a contains oxygen at a higher proportion than the stoichiometric composition. Furthermore, the oxide semiconductor film 19a, the oxide insulating film 23, and the oxide insulating film 25 are surrounded by the nitride insulating film 15 and the oxide insulating film 17. As a result, oxygen contained in the oxide insulating film 23 or the oxide insulating film 25 is moved to the oxide semiconductor film 19a efficiently, so that the amount of oxygen vacancies in the oxide semiconductor film 19a can be reduced. Accordingly, a transistor having normally-off characteristic is obtained. Furthermore, the amount of change in electrical characteristics, typically in threshold voltage, of the transistor over time or due to a stress test can be reduced.
  • the common electrode 29 is formed using a light-transmitting film, preferably a light-transmitting conductive film.
  • a light-transmitting conductive film an indium oxide film containing tungsten oxide, an indium zinc oxide film containing tungsten oxide, an indium oxide film containing titanium oxide, an indium tin oxide film containing titanium oxide, an ITO film, an indium zinc oxide film, an indium tin oxide film to which silicon oxide is added, and the like are given.
  • the common electrode 29 may be formed using the oxide semiconductor film 155b having conductivity in Embodiment 1.
  • the extending direction of the conductive film 21a functioning as a signal line and the extending direction of the common electrode 29 intersect with each other. Therefore, differences in directions between the electric field between the conductive film 21a functioning as a signal line and the common electrode 29 and the electric field between the pixel electrode formed using the oxide semiconductor film 19b having conductivity and the common electrode 29 arise and the differences form a large angle. Accordingly, in the case where negative liquid crystal molecules are used, the alignment state of the liquid crystal molecules in the vicinity of the conductive film functioning as a signal line and the alignment state of the liquid crystal molecules in the vicinity of the pixel electrode which is generated by an electric field between the pixel electrodes provided in adjacent pixels and the common electrode are less likely to be affected by each other. Thus, a change in the transmittance of the pixels is suppressed. Accordingly, flickers in an image can be reduced.
  • the liquid crystal display device having a low refresh rate alignment of liquid crystal molecules in the vicinity of the conductive film 21a functioning as a signal line is less likely to affect alignment state of liquid crystal molecules in the vicinity of the pixel electrode due to the electric field between the pixel electrodes in the adjacent pixels and the common electrode 29 even during the retention period.
  • the transmittance of the pixels in the retention period can be held and flickers can be reduced.
  • the common electrode 29 includes the stripe regions extending in a direction intersecting with the conductive film 21a functioning as a signal line. Accordingly, in the vicinity of the oxide semiconductor film 19b having conductivity and the conductive film 21a, unintended alignment of liquid crystal molecules can be prevented and thus light leakage can be suppressed. As a result, a display device with excellent contrast can be manufactured.
  • the shape of the common electrode 29 is not limited to that illustrated in FIG. 16, and may be stripe. In the case of a stripe shape, the extending direction may be parallel to the conductive film functioning as a signal line.
  • the common electrode 29 may have a comb shape.
  • the common electrode may be formed over the entire surface of the first substrate 11. Further alternatively, a light-transmitting conductive film different from the oxide semiconductor film 19b having conductivity may be formed over the common electrode 29 with an insulating film provided therebetween.
  • the thickness of the organic insulating film 31 is preferably greater than or equal to 500 nm and less than or equal to 10 ⁇ .
  • the thickness of the organic insulating film 31 in FIG. 17 is smaller than a gap between the inorganic insulating film 30 formed over the first substrate 11 and the element layer formed on the second substrate 342. Therefore, the liquid crystal layer 320 is provided between the organic insulating film 31 and the element layer formed on the second substrate 342. In other words, the liquid crystal layer 320 is provided between the alignment film 33 over the organic insulating film 31 and an alignment film 352 included in the element layer on the second substrate 342.
  • the alignment film 33 over the organic insulating film 31 and the alignment film 352 included in the element layer on the second substrate 342 may be in contact with each other.
  • the organic insulating film 31 functions as a spacer; therefore, the cell gap of the liquid crystal display device can be maintained with the organic insulating film 31.
  • the alignment film 33 is provided over the organic insulating film in
  • FIG. 17 one embodiment of the present invention is not limited thereto.
  • the organic insulating film 31 may be provided over the alignment film 33.
  • a rubbing step may be performed after the formation of the organic insulating film 31 over the alignment film 33 instead of directly after the formation of the alignment film 33, for example.
  • the surface of the inorganic insulating film 30 is positively charged, so that an electric field is generated and the electric field affects the interface between the oxide semiconductor film 19a and the inorganic insulating film 30.
  • the interface between the oxide semiconductor film 19a and the inorganic insulating film 30 is substantially in a state to which a positive bias is applied and therefore the threshold voltage of the transistor shifts in the negative direction.
  • the transistor 102 illustrated in this embodiment includes the organic insulating film 31 over the inorganic insulating film 30. Since the thickness of the organic insulating film 31 is as large as 500 nm or more, the electric field generated by application of a negative voltage to the conductive film 13 functioning as a gate electrode does not affect the surface of the organic insulating film 31 and the surface of the organic insulating film 31 is not positively charged easily.
  • the electric field of the positively charged particle adsorbed on the surface of the organic insulating film 31 is less likely to affect the interface between the oxide semiconductor film 19a and the inorganic insulating film 30, because the organic insulating film 31 is thick (greater than or equal to 500 nm).
  • the interface between the oxide semiconductor film 19a and the inorganic insulating film 30 is not substantially a state to which a positive bias is applied and therefore the amount of change in threshold voltage of the transistor is small.
  • the alignment film 33 is formed over the common electrode 29, the nitride insulating film 27, and the organic insulating film 31.
  • FIGS. 18A to 18D a method for manufacturing the transistor 102 and the capacitor 105 in FIG. 17 is described with reference to FIGS. 18A to 18D, FIGS. 19A to 19C, FIGS. 20A to 20C, and FIGS. 21 A and 21B.
  • a conductive film 12 to be the conductive film 13 is formed over the first substrate 11.
  • the conductive film 12 is formed by a sputtering method, a chemical vapor deposition (CVD) method such as a metal organic chemical vapor deposition (MOCVD) method, a metal chemical deposition method, an atomic layer deposition (ALD) method, or a plasma-enhanced chemical vapor deposition (PECVD) method, an evaporation method, a pulsed laser deposition (PLD) method, or the like.
  • MOCVD metal organic chemical vapor deposition
  • ALD atomic layer deposition
  • the conductive film is less damaged by plasma.
  • the manufacturing method of the oxide semiconductor film 155b having conductivity can be used as appropriate.
  • a glass substrate is used as the first substrate 11. Furthermore, as the conductive film 12, a 100-nm-thick tungsten film is formed by a sputtering method.
  • a mask is formed over the conductive film 12 by a photolithography process using a first photomask. Then, as illustrated in FIG. 18B, part of the conductive film 12 is etched with the use of the mask to form the conductive film 13 functioning as a gate electrode. After that, the mask is removed.
  • the conductive film 13 functioning as a gate electrode may be formed by an electrolytic plating method, a printing method, an ink-jet method, or the like instead of the above formation method.
  • the tungsten film is etched by a dry etching method to form the conductive film 13 functioning as a gate electrode.
  • the nitride insulating film 15 and an oxide insulating film 16 to be the oxide insulating film 17 later are formed.
  • an oxide semiconductor film 18 to be the oxide semiconductor film 19a and the oxide semiconductor film 19b having conductivity later is formed.
  • the nitride insulating film 15 and the oxide insulating film 16 are each formed by a sputtering method, a chemical vapor deposition (CVD) method such as a metal organic chemical vapor deposition (MOCVD) method, a metal chemical deposition method, an atomic layer deposition (ALD) method, or a plasma-enhanced chemical vapor deposition (PECVD) method, an evaporation method, a pulsed laser deposition (PLD) method, a coating method, a printing method, or the like.
  • CVD chemical vapor deposition
  • MOCVD metal organic chemical vapor deposition
  • ALD atomic layer deposition
  • PECVD plasma-enhanced chemical vapor deposition
  • PLD pulsed laser deposition
  • MOCVD metal organic chemical vapor deposition
  • ALD atomic layer deposition
  • nitride insulating film 15 a 300-nm-thick silicon nitride film is formed by a plasma CVD method in which silane, nitrogen, and ammonia are used as a source gas.
  • a deposition gas containing silicon and an oxidizing gas are preferably used as a source gas.
  • the deposition gas containing silicon include silane, disilane, trisilane, and silane fluoride.
  • oxygen, ozone, dinitrogen monoxide, and nitrogen dioxide can be given as examples.
  • MOCVD metal organic chemical vapor deposition
  • a 50-nm-thick silicon oxynitride film is formed by a plasma CVD method in which silane and dinitrogen monoxide are used as a source gas.
  • the oxide semiconductor film 18 can be formed by a method that is similar to that of the oxide semiconductor film 155 described in Embodiment 1 as appropriate.
  • the oxide semiconductor film 18 is partly etched using the mask.
  • the oxide semiconductor film 19a and an oxide semiconductor film 19c which are isolated from each other as illustrated in FIG. 18D are formed. After that, the mask is removed.
  • the oxide semiconductor films 19a and 19c are formed in such a manner that a mask is formed over the oxide semiconductor film 18 and part of the oxide semiconductor film 18 is etched by a wet etching method.
  • the conductive film 20 is a stack of a conductive film 20 1 and a conductive film 20 2.
  • the conductive films 20 1, a Cu-X alloy film is used.
  • the conductive films 20 2 a conductive film including a low-resistance material is used.
  • the conductive film 20 can be formed by a method similar to that of the conductive film 159 described in Embodiment 1 as appropriate.
  • a 50-nm-thick Cu-Mn alloy film and a 300-nm-thick copper film are sequentially stacked by a sputtering method.
  • a mask is formed over the conductive film 20 by a photolithography process using a third photomask. Then, the conductive film 20 is etched using the mask, so that the conductive films 21a and 21b serving as a source electrode and a drain electrode are formed as illustrated in FIG. 19B. After that, the mask is removed.
  • the conductive film 21a is a stack of the conductive film 21a_l formed by etching part of the conductive film 20 1 and the conductive film 21a_2 formed by etching part of the conductive film 20 2.
  • the conductive film 21b is a stack of the conductive film 21b_l formed by etching part of the conductive film 20 1 and the conductive film 21b_2 formed by etching part of the conductive film 20 2.
  • a mask is formed over the copper film by a photolithography process. Then, the Cu-Mn film and the copper film are etched with the use of the mask, so that the conductive films 21a and 21b are formed. By using a wet etching method, the Cu-Mn film and the copper film can be etched in one step.
  • an oxide insulating film 22 to be the oxide insulating film 23 later and an oxide insulating film 24 to be the oxide insulating film 25 later are formed over the oxide semiconductor films 19a and 19c and the conductive films 21a and 21b.
  • the oxide insulating film 22 and the oxide insulating film 24 can each be formed by a method similar to those of the nitride insulating film 15 and the oxide insulating film 16 as appropriate.
  • the oxide insulating film 24 is preferably formed in succession without exposure to the air.
  • the oxide insulating film 24 is formed in succession by adjusting at least one of the flow rate of a source gas, pressure, a high-frequency power, and a substrate temperature without exposure to the air, whereby the impurity concentration attributed to the atmospheric component at the interface between the oxide insulating film 22 and the oxide insulating film 24 can be reduced and oxygen in the oxide insulating film 24 can be moved to the oxide semiconductor film 19a; accordingly, the amount of oxygen vacancies in the oxide semiconductor film 19a can be reduced.
  • the oxide insulating film 22 can be formed using an oxide insulating film containing nitrogen and having a small number of defects which is formed by a CVD method under the conditions where the ratio of an oxidizing gas to a deposition gas is higher than 20 times and lower than 100 times, preferably higher than or equal to 40 times and lower than or equal to 80 times and the pressure in a treatment chamber is lower than 100 Pa, preferably lower than or equal to 50 Pa.
  • a deposition gas containing silicon and an oxidizing gas are preferably used as the source gas of the oxide insulating film 22.
  • Typical examples of the deposition gas containing silicon include silane, disilane, trisilane, and silane fluoride.
  • oxygen, ozone, dinitrogen monoxide, and nitrogen dioxide can be given as examples.
  • an oxide insulating film which permeates oxygen can be formed as the oxide insulating film 22. Furthermore, by providing the oxide insulating film 22, damage to the oxide semiconductor film 19a can be reduced in the step of forming the oxide insulating film 24.
  • a 50-nm-thick silicon oxynitride film is formed by a plasma CVD method in which silane with a flow rate of 50 seem and dinitrogen monoxide with a flow rate of 2000 seem are used as a source gas, the pressure in the treatment chamber is 20 Pa, the substrate temperature is 220 °C, and a high-frequency power of 100 W is supplied to parallel-plate electrodes with the use of a 27.12 MHz high-frequency power source. Under the above conditions, a silicon oxynitride film containing nitrogen and having a small number of defects can be formed.
  • a silicon oxide film or a silicon oxynitride film is formed under the following conditions: the substrate placed in a treatment chamber of a plasma CVD apparatus that is vacuum-evacuated is held at a temperature higher than or equal to 180 °C and lower than or equal to 280 °C, preferably higher than or equal to 200 °C and lower than or equal to 240 °C, the pressure is greater than or equal to 100 Pa and less than or equal to 250 Pa, preferably greater than or equal to 100 Pa and less than or equal to 200 Pa with introduction of a source gas into the treatment chamber, and a high-frequency power of greater than or equal to 0.17 W/cm 2 and less than or equal to 0.5 W/cm 2 , preferably greater than or equal to 0.25 W/cm 2 and less than or equal to 0.35 W/cm 2 is supplied to an electrode provided in the treatment chamber.
  • a deposition gas containing silicon and an oxidizing gas are preferably used as the source gas of the oxide insulating film 24.
  • Typical examples of the deposition gas containing silicon include silane, disilane, trisilane, and silane fluoride.
  • oxygen, ozone, dinitrogen monoxide, and nitrogen dioxide can be given as examples.
  • the high-frequency power having the above power density is supplied to the treatment chamber having the above pressure, whereby the degradation efficiency of the source gas in plasma is increased, oxygen radicals are increased, and oxidation of the source gas is promoted; therefore, the oxygen content in the oxide insulating film 24 becomes higher than that in the stoichiometric composition.
  • the bond between silicon and oxygen is weak, and accordingly, part of oxygen in the film is released by heat treatment in a later step.
  • the oxide insulating film 22 is provided over the oxide semiconductor film 19a. Accordingly, in the step of forming the oxide insulating film 24, the oxide insulating film 22 serves as a protective film of the oxide semiconductor film 19a. Consequently, the oxide insulating film 24 can be formed using the high-frequency power having a high power density while damage to the oxide semiconductor film 19a is reduced.
  • a 400-nm-thick silicon oxynitride film is formed by a plasma CVD method in which silane with a flow rate of 200 seem and dinitrogen monoxide with a flow rate of 4000 seem are used as the source gas, the pressure in the treatment chamber is 200 Pa, the substrate temperature is 220 °C, and a high-frequency power of 1500 W is supplied to the parallel-plate electrodes with the use of a 27.12 MHz high-frequency power source.
  • the plasma CVD apparatus is a parallel-plate plasma CVD apparatus in which the electrode area is 6000 cm 2 , and the power per unit area (power density) into which the supplied power is converted is 0.25 W/cm 2 .
  • the oxide semiconductor film 19a is damaged by the etching of the conductive film, so that oxygen vacancies are generated on the back channel side of the oxide semiconductor film 19a (the side of the oxide semiconductor film 19a which is opposite to the side facing the conductive film 13 functioning as a gate electrode).
  • the oxide insulating film which contains oxygen at a higher proportion than the stoichiometric composition as the oxide insulating film 24 the oxygen vacancies generated on the back channel side can be repaired by heat treatment. By this, defects contained in the oxide semiconductor film 19a can be reduced, and thus, the reliability of the transistor 102 can be improved.
  • a mask is formed over the oxide insulating film 24 by a photolithography process using a fourth photomask.
  • part of the oxide insulating film 22 and part of the oxide insulating film 24 are etched with the use of the mask to form the oxide insulating film 23 and the oxide insulating film 25 having the opening 40. After that, the mask is removed.
  • the oxide insulating films 22 and 24 are preferably etched by a dry etching method.
  • the oxide semiconductor film 19c is exposed to plasma in the etching treatment; thus, the amount of oxygen vacancies in the oxide semiconductor film 19c can be increased.
  • the heat treatment is performed typically at a temperature higher than or equal to 150 °C and lower than or equal to 400 °C, preferably higher than or equal to 300 °C and lower than or equal to 400 °C, further preferably higher than or equal to 320 °C and lower than or equal to 370 °C.
  • An electric furnace, an RTA apparatus, or the like can be used for the heat treatment.
  • the heat treatment can be performed at a temperature higher than or equal to the strain point of the substrate if the heating time is short. Therefore, the heat treatment time can be shortened.
  • the heat treatment may be performed under an atmosphere of nitrogen, oxygen, ultra-dry air (air in which a water content is 20 ppm or less, preferably 1 ppm or less, further preferably 10 ppb or less), or a rare gas (argon, helium, or the like).
  • the atmosphere of nitrogen, oxygen, ultra-dry air, or a rare gas preferably does not contain hydrogen, water, and the like.
  • part of oxygen contained in the oxide insulating film 25 can be moved to the oxide semiconductor film 19a, so that the amount of oxygen vacancies contained in the oxide semiconductor film 19a can be further reduced.
  • oxide insulating film 24 when the oxide insulating film 24 is formed over the oxide insulating film 22 while being heated, oxygen can be moved to the oxide semiconductor film 19a to reduce the amount of oxygen vacancies in the oxide semiconductor film 19a; thus, the heat treatment is not necessarily performed.
  • the heat treatment may be performed after the formation of the oxide insulating films 22 and 24.
  • the heat treatment is preferably performed after the formation of the oxide insulating films 23 and 25 because a film having higher conductivity can be formed in such a manner that oxygen is not moved to the oxide semiconductor film 19c and oxygen is released from the oxide semiconductor film 19c because of exposure of the oxide semiconductor film 19c and then oxygen vacancies are generated.
  • the heat treatment is performed at 350 °C in a mixed atmosphere of nitrogen and oxygen for one hour.
  • the nitride insulating film 26 is formed.
  • the nitride insulating film 26 can be formed by a method similar to those of the nitride insulating film 15 and the oxide insulating film 16 as appropriate. By forming the nitride insulating film 26 by a sputtering method, a CVD method, or the like, the oxide semiconductor film 19c is exposed to plasma; thus, the amount of oxygen vacancies in the oxide semiconductor film 19c can be increased.
  • the oxide semiconductor film 19c has improved conductivity, and becomes the oxide semiconductor film 19b having conductivity.
  • a silicon nitride film is formed by a plasma CVD method as the nitride insulating film 26
  • hydrogen contained in the silicon nitride film is diffused to the oxide semiconductor film 19c; thus, the conductivity of the oxide semiconductor film can be enhanced.
  • the manufacturing method of the oxide semiconductor film 19b having conductivity the manufacturing method of the oxide semiconductor film 155b having conductivity in Embodiment 1 can be used.
  • the substrate placed in the treatment chamber of the plasma CVD apparatus that is vacuum-evacuated is preferably held at a temperature higher than or equal to 300 °C and lower than or equal to 400 °C, further preferably higher than or equal to 320 °C and lower than or equal to 370 °C, so that a dense silicon nitride film can be formed.
  • a deposition gas containing silicon, nitrogen, and ammonia are preferably used as a source gas.
  • the source gas a small amount of ammonia compared to the amount of nitrogen is used, whereby ammonia is dissociated in the plasma and activated species are generated.
  • the activated species cleave a bond between silicon and hydrogen which are contained in a deposition gas containing silicon and a triple bond between nitrogen molecules.
  • the flow ratio of the nitrogen to the ammonia is set to be preferably greater than or equal to 5 and less than or equal to 50, further preferably greater than or equal to 10 and less than or equal to 50.
  • a 50-nm-thick silicon nitride film is formed as the nitride insulating film 26 by a plasma CVD method in which silane with a flow rate of 50 seem, nitrogen with a flow rate of 5000 seem, and ammonia with a flow rate of 100 seem are used as the source gas, the pressure in the treatment chamber is 100 Pa, the substrate temperature is 350 °C, and a high-frequency power of 1000 W is supplied to parallel -plate electrodes with a high-frequency power supply of 27.12 MHz.
  • the plasma CVD apparatus is a parallel-plate plasma CVD apparatus in which the electrode area is 6000 cm 2 , and the power per unit area (power density) into which the supplied power is converted is 1.7 x 10 "1 W/cm 2 .
  • heat treatment may be performed.
  • the heat treatment is performed typically at a temperature higher than or equal to 150 °C and lower than or equal to 400 °C, preferably higher than or equal to 300 °C and lower than or equal to 400 °C, further preferably higher than or equal to 320 °C and lower than or equal to 370 °C.
  • the negative shift of the threshold voltage can be reduced.
  • the amount of change in the threshold voltage can be reduced.
  • a mask is formed by a photolithography process using a fifth photomask. Then, part of each of the nitride insulating film 15, the oxide insulating film 16, the oxide insulating film 23, the oxide insulating film 25, and the nitride insulating film 26 is etched using the mask to form the nitride insulating film 27 and an opening through which part of a connection terminal formed at the same time as the conductive film 13 is exposed.
  • part of each of the oxide insulating film 23, the oxide insulating film 25, and the nitride insulating film 26 is etched to form the nitride insulating film 27 and an opening through which part of a connection terminal formed at the same time as the conductive films 21a and 21b is exposed.
  • a conductive film 28 to be the common electrode 29 later is formed over the nitride insulating film 27.
  • the conductive film 28 is formed by a sputtering method, a CVD method, an evaporation method, or the like.
  • the manufacturing method of the oxide semiconductor film 155b having conductivity can be used as appropriate.
  • a mask is formed over the conductive film 28 by a photolithography process using a sixth photomask.
  • part of the conductive film 28 is etched with the use of the mask to form the common electrode 29.
  • the common electrode 29 is connected to the connection terminal formed at the same time as the conductive film 13 or the connection terminal formed at the same time as the conductive films 21a and 21b. After that, the mask is removed.
  • the organic insulating film 31 is formed over the nitride insulating film 27.
  • An organic insulating film can be formed by a coating method, a printing method, or the like as appropriate.
  • a photosensitive composition with which the upper surfaces of the nitride insulating film 27 and the common electrode 29 are coated, is exposed to light and developed by photolithography process using a seventh photomask, and is then subjected to heat treatment.
  • a resist with which the upper surface of the non-photosensitive composition is coated, is processed by a photolithography process using a seventh mask to form a mask, and then the non-photosensitive composition is etched using the mask, whereby the organic insulating film 31 can be formed.
  • the transistor 102 is manufactured and the capacitor 105 can be manufactured.
  • the conductive film 21b including the Cu-X alloy film is formed over the oxide semiconductor film 19b having conductivity, whereby the adhesion between the oxide semiconductor film 19b having conductivity and the conductive film 21b can be increased and the contact resistance between them can be reduced.
  • the element substrate of the display device described in this embodiment includes an organic insulating film overlapping with a transistor with an inorganic insulating film provided therebetween. Therefore, a display device in which reliability of the transistor can be improved and whose display quality is maintained can be manufactured.
  • the element substrate of the display device of this embodiment is provided with a common electrode whose upper surface has a zigzag shape and which includes stripe regions extending in a direction intersecting with the conductive film functioning as a signal line. Therefore, the display device can have excellent contrast. In addition, flickers can be reduced in a liquid crystal display device having a low refresh rate.
  • the oxide semiconductor film having conductivity serving as the pixel electrode is formed at the same time as the oxide semiconductor film of the transistor, in which the channel region is formed; therefore, the transistor 102 and the capacitor 105 can be formed using six photomasks.
  • the oxide semiconductor film having conductivity functions as the one of electrodes of the capacitor.
  • the common electrode also functions as the other of electrodes of the capacitor.
  • a step of forming another conductive film is not needed to form the capacitor, and the number of steps of manufacturing the display device can be reduced.
  • the capacitor has a light-transmitting property. As a result, the area occupied by the capacitor can be increased and the aperture ratio in a pixel can be increased. Moreover, power consumption of the display device can be reduced.
  • a film having a colored property (hereinafter referred to as a coloring film 346) is formed on the second substrate 342.
  • the coloring film 346 functions as a color filter.
  • a light-blocking film 344 adjacent to the coloring film 346 is formed on the second substrate 342.
  • the light-blocking film 344 functions as a black matrix.
  • the coloring film 346 is not necessarily provided in the case where the liquid crystal display device is a monochrome display device, for example.
  • the coloring film 346 is a coloring film that transmits light in a specific wavelength range.
  • a red (R) film for transmitting light in a red wavelength range a green (G) film for transmitting light in a green wavelength range, a blue (B) film for transmitting light in a blue wavelength range, or the like can be used.
  • the light-blocking film 344 preferably has a function of blocking light in a specific wavelength range, and can be a metal film or an organic insulating film including a black pigment or the like, for example.
  • An insulating film 348 is formed on the coloring film 346.
  • the insulating film 348 functions as a planarization layer or suppresses diffusion of impurities in the coloring film 346 to the liquid crystal element side.
  • a conductive film 350 is formed on the insulating film 348.
  • the conductive film 350 is formed using a light-transmitting conductive film.
  • the potential of the conductive film 350 is preferably the same as that of the common electrode 29. In other words, a common potential is preferably applied to the conductive film 350.
  • the alignment film 352 is formed on the conductive film 350.
  • liquid crystal layer 320 is formed between the alignment films 33 and 352.
  • the liquid crystal layer 320 is sealed between the first substrate 11 and the second substrate 342 with the use of a sealant (not illustrated).
  • the sealant is preferably in contact with an inorganic material to prevent entry of moisture and the like from the outside.
  • a spacer may be provided between the alignment films 33 and 352 to maintain the thickness of the liquid crystal layer 320 (also referred to as a cell gap).
  • FIG. 22 illustrates a modification example of the display device in FIG. 17.
  • an organic resin film is not formed over the inorganic insulating film 30, and the alignment film 33 is in contact with the whole of the inorganic insulating film 30.
  • the number of photomasks for forming the element portion over the first substrate 11 can be reduced, and simplification of the manufacturing process of the first substrate 11 provided with the element portion can be achieved.
  • FIG. 23 illustrates a modification example of the display device in FIG. 17.
  • a continuous organic resin film 31a that is not divided is formed over the nitride insulating film 27. Furthermore, the common electrode 29 is formed over the organic resin film 31a.
  • the organic resin film 31a serves as a planarization film; thus, irregularity in alignment of liquid crystal molecules included in the liquid crystal layer can be reduced.
  • FIG. 24 illustrates a modification example of the display device in FIG. 17.
  • the oxide semiconductor film 19b having conductivity that serves as a pixel electrode in FIG. 24 has a slit. Note that the oxide semiconductor film 19b having conductivity may have a comb-like shape.
  • FIG. 25 illustrates a modification example of the display device in FIG. 17.
  • the common electrode 29 in FIG. 25 overlaps with the conductive film 21b with the nitride insulating film 27 provided therebetween.
  • the common electrode 29, the nitride insulating film 27, and the conductive film 21b constitute a capacitor 105b. By providing the capacitor 105b, the capacitance value in the pixel can be increased.
  • FIGS. 26A and 26B illustrate modification examples of the transistor 102 in
  • a transistor 102d illustrated in FIG. 26A includes an oxide semiconductor film 19g and a pair of conductive films 21c and 2 Id, which are formed with a multi-tone photomask.
  • the conductive film 21c has a stacked-layer structure of a conductive film 21c_l and a conductive film 21c_2.
  • the conductive film 2 Id has a stacked-layer structure of a conductive film 21d_l and a conductive film 21d_2.
  • a Cu-X alloy film is used.
  • As the conductive films 21c_2 and 21d_2, a conductive film including a low-resistance material is used.
  • a resist mask having a plurality of thicknesses can be formed. After the oxide semiconductor film 19g is formed with the resist mask, the resist mask is exposed to oxygen plasma or the like and is partly removed; accordingly, a resist mask for forming a pair of conductive films is formed. Therefore, the number of steps in the photolithography process in the process of forming the oxide semiconductor film 19g and the pair of conductive films 21c and 21d can be reduced.
  • the oxide semiconductor film 19g formed with a multi-tone photomask is partly exposed when seen from the above.
  • a transistor 102e illustrated in FIG. 26B is a channel-protective transistor.
  • the transistor 102e illustrated in FIG. 26B includes the conductive film 13 functioning as a gate electrode provided over the first substrate 11, the gate insulating film 14 formed over the first substrate 11 and the conductive film 13 functioning as a gate electrode, the oxide semiconductor film 19a overlapping with the conductive film 13 functioning as a gate electrode with the gate insulating film 14 provided therebetween, an inorganic insulating film 30a covering a channel region and side surfaces of the oxide semiconductor film 19a, and conductive films 21e and 2 If functioning as a source electrode and a drain electrode in contact with the oxide semiconductor film 19a in an opening of the inorganic insulating film 30a.
  • the conductive film 21e has a stacked-layer structure of a conductive film 2 le i and a conductive film 21e_2.
  • the conductive film 21f has a stacked-layer structure of a conductive film 21f_l and a conductive film 21f_2.
  • a Cu-X alloy film is used as the conductive films 21e l and 21f_l.
  • a conductive film including a low-resistance material is used as the conductive films 21e_2 and 21f_2.
  • the oxide semiconductor film 19a is not damaged by etching for forming the conductive films 21e and 21f because the oxide semiconductor film 19a is covered with the inorganic insulating film 30a. Therefore, defects in the oxide semiconductor film 19a can be reduced.
  • a liquid crystal display device driven in a vertical alignment (VA) mode will be described.
  • VA vertical alignment
  • a conductive film 13 functioning as a scan line extends in a direction substantially perpendicularly to a conductive film functioning as a signal line (in the lateral direction in the drawing).
  • the conductive film 21a functioning as a signal line extends in a direction substantially perpendicularly to the conductive film functioning as a scan line (in the longitudinal direction in the drawing).
  • a conductive film 21g functioning as a capacitor line extends in a direction parallel to the signal line. Note that the conductive film 13 functioning as a scan line is electrically connected to the scan line driver circuit 104 (see FIG. 15 A), and the conductive film 21a functioning as a signal line and the conductive film 21g functioning as a capacitor line is electrically connected to the signal line driver circuit 106 (see FIG. 15 A).
  • the transistor 102 is provided in a region where the conductive film functioning as a scan line and the conductive film functioning as a signal line intersect with each other.
  • the transistor 102 includes the conductive film 13 functioning as a gate electrode; a gate insulating film (not illustrated in FIG. 27); the oxide semiconductor film 19a where a channel region is formed, over the gate insulating film; and the conductive films 21a and 21b functioning as a pair of electrodes.
  • the conductive film 13 also functions as a scan line, and a region of the conductive film 13 that overlaps with the oxide semiconductor film 19a functions as the gate electrode of the transistor 102.
  • the conductive film 21a also functions as a signal line, and a region of the conductive film 21a that overlaps with the oxide semiconductor film 19a functions as the source electrode or the drain electrode of the transistor 102. Furthermore, in the top view of FIG. 27, an end portion of the conductive film functioning as a scan line is positioned on an outer side of an end portion of the oxide semiconductor film 19a. Thus, the conductive film functioning as a scan line functions as a light-blocking film for blocking light from a light source such as a backlight. For this reason, the oxide semiconductor film 19a included in the transistor is not irradiated with light, so that a variation in the electrical characteristics of the transistor can be suppressed.
  • the transistor 102 includes the organic insulating film 31 overlapping with the oxide semiconductor film 19a in a manner similar to that in Embodiment 4.
  • the organic insulating film 31 overlaps with the oxide semiconductor film 19a (in particular, a region of the oxide semiconductor film 19a which is between the conductive films 21a and 21b) with an inorganic insulating film (not illustrated in FIG. 27) provided therebetween.
  • the conductive film 21b is electrically connected to a light-transmitting conductive film 29c that functions as a pixel electrode in an opening 41.
  • the capacitor 105 is connected to the conductive film 21g functioning as a capacitor line.
  • the capacitor 105 includes an oxide semiconductor film 19d having conductivity formed over the gate insulating film, a dielectric film formed over the transistor 102, and the light-transmitting conductive film 29c functioning as a pixel electrode.
  • the oxide semiconductor film 19d having conductivity formed over the gate insulating film has a light-transmitting property. That is, the capacitor 105 has a light-transmitting property.
  • the capacitor 105 can be formed large (in a large area) in the pixel 103.
  • a display device with a large-capacitance capacitor as well as an aperture ratio increased to typically 55 % or more, preferably 60 % or more can be provided.
  • the area of a pixel is small and accordingly the area of a capacitor is also small. For this reason, the amount of charges accumulated in the capacitor is small in the high-resolution display device.
  • the capacitor 105 of this embodiment has a light-transmitting property, when the capacitor 105 is provided in a pixel, a sufficient capacitance value can be obtained in the pixel and the aperture ratio can be improved.
  • the capacitor 105 can be favorably used for a high-resolution display device with a pixel density of 200 pixels per inch (ppi) or more, 300 ppi or more, or furthermore, 500 ppi or more.
  • the aperture ratio can be improved even in a high-resolution display device, which makes it possible to use light from a light source such as a backlight efficiently, so that power consumption of the display device can be reduced.
  • FIG. 28 is a cross-sectional view taken along dashed-dotted lines A-B and C-D in FIG. 27.
  • the transistor 102 illustrated in FIG. 27 is a channel-etched transistor. Note that the transistor 102 in the channel length direction, a connection portion between the transistor 102 and the light-transmitting conductive film 29c functioning as a pixel electrode, and the capacitor 105 are illustrated in the cross-sectional view taken along dashed-dotted line A-B, and the transistor 102 in the channel width direction is illustrated in the cross-sectional view taken along dashed-dotted line C-D.
  • a liquid crystal element 322 includes the light-transmitting conductive film 29c functioning as a pixel electrode included in the element layer of the first substrate 11, the conductive film 350 included in the element layer of the second substrate 342, and the liquid crystal layer 320.
  • the transistor 102 in FIG. 28 has a structure similar to that of the transistor 102 in Embodiment 4.
  • the light-transmitting conductive film 29c functioning as a pixel electrode connected to one of the conductive films 21a and 21b functioning as a source electrode and a drain electrode (here, connected to the conductive film 21b) is formed over the nitride insulating film 27.
  • the conductive film 21b is connected to the light-transmitting conductive film 29c functioning as a pixel electrode.
  • the light-transmitting conductive film 29c functioning as a pixel electrode can be formed using as appropriate a material and a manufacturing method similar to those of the common electrode 29 in Embodiment 4.
  • the capacitor 105 in FIG. 28 includes the oxide semiconductor film 19d having conductivity formed over the oxide insulating film 17, the nitride insulating film 27, and the light-transmitting conductive film 29c functioning as a pixel electrode.
  • the oxide insulating films 23 and 24 are formed over the transistor 102 in this embodiment.
  • the oxide insulating films 23 and 25 which are isolated from each other overlap with the oxide semiconductor film 19a.
  • the organic insulating film 31 overlapping with the oxide semiconductor film 19a is provided over the nitride insulating film 27.
  • the organic insulating film 31 overlapping with the oxide semiconductor film 19a is provided over the transistor 102, whereby the surface of the oxide semiconductor film 19a can be made apart from the surface of the organic insulating film 31.
  • the surface of the oxide semiconductor film 19a is not affected by the electric field of positively charged particles adsorbed on the surface of the organic insulating film 31 and therefore the reliability of the transistor 102 can be improved.
  • the oxide semiconductor film 19d having conductivity is different from that in Embodiment 4 and is not connected to the conductive film 21b.
  • the oxide semiconductor film 19d having conductivity is in contact with a conductive film 2 Id.
  • the conductive film 21d serves as a capacitor line.
  • the oxide semiconductor film 19d having conductivity can be formed in a manner similar to that of the oxide semiconductor film 19b having conductivity in Embodiment 4. That is, the oxide semiconductor film 19d having conductivity is a metal oxide film containing the same metal element as the oxide semiconductor film 19a.
  • FIG. 28 is described with reference to FIGS. 29A to 29C and FIGS. 30Ato 30C.
  • a conductive film is formed over the first substrate 11 and then etched using a mask formed through the first photolithography process in Embodiment 4, whereby the conductive film 13 functioning as a gate electrode is formed over the first substrate 11 (see FIG. 29A).
  • the nitride insulating film 15 and the oxide insulating film 16 are formed over the first substrate 11 and the conductive film 13 functioning as a gate electrode.
  • an oxide semiconductor film is formed over the oxide insulating film 16 and then etched using a mask formed through the second photolithography process in Embodiment 4, whereby the oxide semiconductor films 19a and 19c are formed (see FIG. 29B).
  • a conductive film is formed over the oxide insulating film 16 and the oxide semiconductor films 19a and 19c and then etched using a mask formed through the third photolithography process in Embodiment 4, whereby the conductive films 21a, 21b, and 21d are formed (see FIG. 29C).
  • the conductive film 21b is formed so as not to be in contact with the oxide semiconductor film 19c.
  • the conductive film 21d is formed so as to be in contact with the oxide semiconductor film 19c.
  • the conductive film 21d_l and the conductive film 21d_2 are stacked.
  • an oxide insulating film is formed over the oxide insulating film 16, the oxide semiconductor films 19a and 19c, and the conductive films 21a, 21b, and 21d and then etched using a mask formed through the fourth photolithography process in Embodiment 4, whereby the oxide insulating films 23 and 25 having the opening 40 are formed (see FIG. 3 OA).
  • a nitride insulating film is formed over the oxide insulating film 17, the oxide semiconductor films 19a and 19c, the conductive films 21a, 21b, and 2 Id, and the oxide insulating films 23 and 25 and then etched using a mask formed through the fifth photolithography process in Embodiment 4, whereby the nitride insulating film 27 having the opening 41 through which part of the conductive film 21b is exposed is formed (see FIG. 30B).
  • the oxide semiconductor film 19c becomes the oxide semiconductor film 19d having conductivity.
  • a silicon nitride film is formed later by a plasma CVD method as the nitride insulating film 27, hydrogen contained in the silicon nitride film is diffused to the oxide semiconductor film 19c; thus, the conductivity of the oxide semiconductor film 19d having conductivity can be enhanced.
  • a conductive film is formed over the conductive film 21b and the nitride insulating film 27 and then etched using a mask formed through the sixth photolithography process in Embodiment 4, whereby the conductive film 29c connected to the conductive film 21b is formed (see FIG. 30C).
  • one electrode of the capacitor is formed at the same time as the oxide semiconductor film of the transistor.
  • the light-transmitting conductive film functioning as a pixel electrode is used as the other electrode of the capacitor.
  • a step of forming another conductive film is not needed to form the capacitor, and the number of steps of manufacturing the display device can be reduced.
  • the capacitor since the pair of electrodes has a light-transmitting property, the capacitor has a light-transmitting property. As a result, the area occupied by the capacitor can be increased and the aperture ratio in a pixel can be increased.
  • the number of masks can be reduced by not etching the oxide insulating film 22 and the oxide insulating film 24 formed over the transistor 102.
  • the nitride insulating film 27 is formed over the oxide insulating film 24, and an opening 41a through which part of the conductive film 21b is exposed is formed in the oxide insulating films 22 and 24 and the nitride insulating film 27.
  • the conductive film 21d is formed over the oxide insulating film 17. Since the conductive film 21d is formed at the same time as the conductive films 21a and 21b are formed, an additional photomask is not needed to form the conductive film 2 Id.
  • the conductive film 21d functions as a capacitor line. That is, a capacitor 105a includes the conductive film 2 Id, the oxide insulating film 22, the oxide insulating film 24, the nitride insulating film 27, and the light-transmitting conductive film 29d functioning as a pixel electrode.
  • a display device which is different from the display devices in Embodiment 4 and a manufacturing method thereof are described with reference to drawings.
  • This embodiment is different from Embodiment 4 in that the transistor has a structure in which an oxide semiconductor film is provided between different gate electrodes, that is, a dual-gate structure. Note that the structures similar to those in Embodiment 4 are not described repeatedly here.
  • the transistor provided in the display device of this embodiment is different from that in Embodiment 4 in that a conductive film 29b functioning as a gate electrode and overlapping part of or the whole of each of the conductive film 13 functioning as a gate electrode, the oxide semiconductor film 19a, the conductive films 21a and 21b, and the oxide insulating film 25 is provided.
  • the conductive film 29b functioning as a gate electrode is connected to the conductive film 13 functioning as a gate electrode in the opening 41a.
  • a transistor 102a illustrated in FIG. 32 is a channel-etched transistor. Note that the transistor 102a in the channel length direction and the capacitor 105a are illustrated in a cross-sectional view in a portion A-B, and the transistor 102a in the channel width direction and a connection portion between the conductive film 13 functioning as a gate electrode and the conductive film 29b functioning as a gate electrode are illustrated in a cross-sectional view in a portion C-D.
  • the transistor 102a in FIG. 32 has a dual -gate structure and includes the conductive film 13 functioning as a gate electrode over the first substrate 11.
  • the transistor 102a includes the nitride insulating film 15 formed over the first substrate 11 and the conductive film 13 functioning as a gate electrode, the oxide insulating film 17 formed over the nitride insulating film 15, the oxide semiconductor film 19a overlapping with the conductive film 13 functioning as a gate electrode with the nitride insulating film 15 and the oxide insulating film 17 provided therebetween, and the conductive films 21a and 21b functioning as a source electrode and a drain electrode which are in contact with the oxide semiconductor film 19a.
  • the oxide insulating film 23 is formed over the oxide insulating film 17, the oxide semiconductor film 19a, and the conductive films 21a and 21b functioning as a source electrode and a drain electrode, and the oxide insulating film 25 is formed over the oxide insulating film 23.
  • the nitride insulating film 27 is formed over the nitride insulating film 15, the oxide insulating film 23, the oxide insulating film 25, and the conductive film 21b.
  • the oxide semiconductor film 19b having conductivity is formed over the oxide insulating film 17.
  • the oxide semiconductor film 19b having conductivity is connected to one of the conductive films 21a and 21b functioning as a source electrode and a drain electrode, here, connected to the conductive film 21b.
  • the common electrode 29 and the conductive film 29b functioning as a gate electrode are formed over the nitride insulating film 27.
  • the conductive film As illustrated in the cross-sectional view in a portion C-D, the conductive film
  • the conductive film 13 functioning as a gate electrode is connected to the conductive film 13 functioning as a gate electrode in the opening 41a provided in the nitride insulating film 15 and the nitride insulating film 27. That is, the conductive film 13 functioning as a gate electrode and the conductive film 29b functioning as a gate electrode have the same potential.
  • the oxide insulating films 23 and 25 are formed.
  • the oxide insulating films 23 and 25 overlap with the oxide semiconductor film 19a.
  • end portions of the oxide insulating films 23 and 25 are positioned on an outer side of an end portion of the oxide semiconductor film 19a.
  • the conductive film 29b functioning as a gate electrode is positioned at end portions of the oxide insulating films 23 and 25.
  • An end portion processed by etching or the like of the oxide semiconductor film is damaged by processing, to produce defects and also contaminated by the attachment of an impurity, or the like.
  • the end portion of the oxide semiconductor film is easily activated by application of a stress such as an electric field, thereby easily becoming n-type (having a low resistance). Therefore, the end portion of the oxide semiconductor film 19a overlapping with the conductive film 13 functioning as a gate electrode easily becomes n-type.
  • the end portion which becomes n-type is provided between the conductive films 21a and 21b functioning as a source electrode and a drain electrode, the region which becomes n-type functions as a carrier path, resulting in a parasitic channel.
  • the oxide semiconductor film having conductivity functioning as the pixel electrode is formed at the same time as the oxide semiconductor film of the transistor.
  • the oxide semiconductor film having conductivity also functions as one of electrodes of the capacitor.
  • the common electrode also functions as the other of electrodes of the capacitor.
  • transistor 102a Details of the transistor 102a are described below. Note that the components with the same reference numerals as those in Embodiment 4 are not described here.
  • the conductive film 29b functioning as a gate electrode can be formed using a material similar to that of the common electrode 29 in Embodiment 4.
  • FIGS. 18A to 18D a method for manufacturing the transistor 102a and the capacitor 105a in FIG. 32 is described with reference to FIGS. 18A to 18D, FIGS. 19A to 19C, FIGS. 20A and 20B, and FIGS. 33 A to 33C.
  • the conductive film 13 functioning as a gate electrode, the nitride insulating film 15, the oxide insulating film 16, the oxide semiconductor film 19a, the oxide semiconductor film 19b having conductivity, the conductive films 21a and 21b functioning as a source electrode and a drain electrode, the oxide insulating film 22, the oxide insulating film 24, and the nitride insulating film 26 are formed over the first substrate 11.
  • photolithography processes using the first photomask to the fourth photomask are performed.
  • a mask is formed over the nitride insulating film 26 through a photolithography process using a fifth photomask, and then part of the nitride insulating film 26 is etched using the mask; thus, the nitride insulating film 27 having the opening 41a is formed as illustrated in FIG. 33 A.
  • the conductive film 28 to be the common electrode 29 and the conductive film 29b functioning as a gate electrode is formed over the conductive film 13 functioning as a gate electrode, and the nitride insulating film 27.
  • a mask is formed over the conductive film 28 by a photolithography process using a sixth photomask.
  • part of the conductive film 28 is etched with the use of the mask to form the common electrode 29 and the conductive film 29b functioning as a gate electrode. After that, the mask is removed.
  • the transistor 102a is manufactured and the capacitor 105a can also be manufactured.
  • the transistor described in this embodiment when the conductive film 29b functioning as a gate electrode faces a side surface of the oxide semiconductor film 19a with the oxide insulating films 23 and 25 provided therebetween in the channel width direction, due to the electric field of the conductive film 29b functioning as a gate electrode, generation of a parasitic channel on the side surface of the oxide semiconductor film 19a or in a region including the side surface and the vicinity of the side surface is suppressed. As a result, a transistor which has excellent electrical characteristics such as a sharp increase in the drain current at the threshold voltage is obtained.
  • the element substrate of the display device of this embodiment is provided with a common electrode including a stripe region extending in a direction intersecting with a signal line. Therefore, the display device can have excellent contrast.
  • the oxide semiconductor film having conductivity functioning as the pixel electrode is formed at the same time as the oxide semiconductor film of the transistor.
  • the oxide semiconductor film having conductivity functions as the one of electrodes of the capacitor.
  • the common electrode also functions as the other of electrodes of the capacitor.
  • a display device including a transistor in which the number of defects in an oxide semiconductor film can be further reduced as compared with the above embodiments is described with reference to drawings.
  • the transistor described in this embodiment is different from any of the transistors in Embodiments 4 to 6 in that a multilayer film including a plurality of oxide semiconductor films is provided.
  • details are described using the transistor in Embodiment 4.
  • FIGS. 34A and 34B each show a cross-sectional view of an element substrate included in a display device.
  • FIGS. 34A and 34B are cross-sectional views taken along dashed-dotted lines A-B and C-D in FIG. 16.
  • a transistor 102b in FIG. 34A includes a multilayer film 37a overlapping with the conductive film 13 functioning as a gate electrode with the nitride insulating film 15 and the oxide insulating film 17 provided therebetween, and the conductive films 21a and 21b functioning as a source electrode and a drain electrode in contact with the multilayer film 37a.
  • the oxide insulating film 23, the oxide insulating film 25, and the nitride insulating film 27 are formed over the nitride insulating film 15, the oxide insulating film 17, the multilayer film 37a, and the conductive films 21a and 21b functioning as a source electrode and a drain electrode.
  • the capacitor 105b in FIG. 34A includes a multilayer film 37b formed over the oxide insulating film 17, the nitride insulating film 27 in contact with the multilayer film 37b, and the common electrode 29 in contact with the nitride insulating film 27.
  • the multilayer film 37b functions as a pixel electrode.
  • the multilayer film 37a includes the oxide semiconductor film 19a and an oxide semiconductor film 39a. That is, the multilayer film 37a has a two-layer structure. In addition, part of the oxide semiconductor film 19a functions as a channel region. Moreover, the oxide insulating film 23 is formed in contact with the multilayer film 37a, and the oxide insulating film 25 is formed in contact with the oxide insulating film 23. That is, the oxide semiconductor film 39a is provided between the oxide semiconductor film 19a and the oxide insulating film 23.
  • the oxide semiconductor film 39a is an oxide film containing one or more elements that constitute the oxide semiconductor film 19a. Thus, interface scattering is unlikely to occur at the interface between the oxide semiconductor films 19a and 39a. Thus, the transistor can have high field-effect mobility because the movement of carriers is not hindered at the interface.
  • the oxide semiconductor film 39a is typically an In-Ga oxide film, an In-Zn oxide film, or an In- -Zn oxide film (M represents Al, Ga, Y, Zr, Sn, La, Ce, or Nd).
  • the energy at the conduction band bottom of the oxide semiconductor film 39a is closer to a vacuum level than that of the oxide semiconductor film 19a is, and typically, the difference between the energy at the conduction band bottom of the oxide semiconductor film 39a and the energy at the conduction band bottom of the oxide semiconductor film 19a is any one of 0.05 eV or more, 0.07 eV or more, 0.1 eV or more, or 0.15 eV or more, and any one of 2 eV or less, 1 eV or less, 0.5 eV or less, or 0.4 eV or less.
  • the difference between the electron affinity of the oxide semiconductor film 39a and the electron affinity of the oxide semiconductor film 19a is any one of 0.05 eV or more, 0.07 eV or more, 0.1 eV or more, or 0.15 eV or more, and any one of 2 eV or less, 1 eV or less, 0.5 eV or less, or 0.4 eV or less.
  • the oxide semiconductor film 39a preferably contains In because carrier mobility (electron mobility) can be increased.
  • any of the following effects may be obtained: (1) the energy gap of the oxide semiconductor film 39a is widened; (2) the electron affinity of the oxide semiconductor films film 39a is reduced; (3) scattering of impurities from the outside is reduced; (4) an insulating property increases as compared to the oxide semiconductor film 19a; and (5) oxygen vacancies are less likely to be generated because Al, Ga, Y, Zr, Sn, La, Ce, or Nd is a metal element strongly bonded to oxygen.
  • the proportions of In and M when the summation of In and M is assumed to be 100 atomic% are preferably as follows: the atomic percentage of In is less than 50 atomic% and the atomic percentage of M is greater than 50 atomic%; further preferably, the atomic percentage of In is less than 25 atomic% and the atomic percentage of M is greater than 75 atomic%.
  • the oxide semiconductor film 39a is an In-M-Zn oxide film (M represents Al, Ga, Y, Zr, Sn, La, Ce, or Nd), the proportion of M atoms (M represents Al, Ga, Y, Zr, Sn, La, Ce, or Nd) in the oxide semiconductor film 39a is higher than that in the oxide semiconductor film 19a.
  • the proportion ofMin the oxide semiconductor film 39a is 1.5 times or more, preferably twice or more, further preferably three times or more as high as that in the oxide semiconductor film 19a.
  • each of the oxide semiconductor film 19a and the oxide semiconductor film 39a is an In-M-Zn oxide film (M represents Al, Ga, Y, Zr, Sn, La, Ce, or Nd)
  • y ⁇ lx ⁇ is higher than y-Jx-i.
  • yi/xi is 1.5 times or more as high as yilxi. Further preferably, is twice or more as high as yilxi. Still further preferably, is three times or more as high as jV 2 .
  • oxide semiconductor film 19a is an In-M-Zn oxide film
  • xi/yi is preferably greater than or equal to 1/3 and less than or equal to 6, further preferably greater than or equal to 1 and less than or equal to 6, and z 1 /y 1 is preferably greater than or equal to 1/3 and less than or equal to 6, further preferably greater than or equal to 1 and less than or equal to 6.
  • z 1 /y 1 is preferably greater than or equal to 1/3 and less than or equal to 6, further preferably greater than or equal to 1 and less than or equal to 6.
  • x 2 /y 2 is preferably less than xi/yi
  • z 2 /y 2 is preferably greater than or equal to 1/3 and less than or equal to 6, further preferably greater than or equal to 1 and less than or equal to 6. Note that when z 2 /y 2 is greater than or equal to 1 and less than or equal to 6, a CAAC-OS film to be described later as the oxide semiconductor film 39a is easily formed.
  • the oxide semiconductor film 39a also functions as a film that relieves damage to the oxide semiconductor film 19a at the time of forming the oxide insulating film 25 later.
  • the thickness of the oxide semiconductor film 39a is greater than or equal to 3 nm and less than or equal to 100 nm, preferably greater than or equal to 3 nm and less than or equal to 50 nm.
  • the oxide semiconductor film 39a can have a crystal structure of the oxide semiconductor film 19a as appropriate.
  • the oxide semiconductor films 19a and 39a may each be a mixed film including two or more of the following: a region having an amorphous structure, a region having a microcrystalline structure, a region having a poly crystalline structure, a CAAC-OS region, and a region having a single-crystal structure.
  • the mixed film has a single-layer structure including, for example, two or more of a region having an amorphous structure, a region having a microcrystalline structure, a region having a polycrystalline structure, a CAAC-OS region, and a region having a single-crystal structure in some cases.
  • the mixed film has a stacked-layer structure in which two or more of the following regions are stacked: a region having an amorphous structure, a region having a microcrystalline structure, a region having a polycrystalline structure, a CAAC-OS region, and a region having a single-crystal structure.
  • the oxide semiconductor film 39a is formed between the oxide semiconductor film 19a and the oxide insulating film 23.
  • carrier traps are formed between the oxide semiconductor film 39a and the oxide insulating film 23 by impurities and defects, electrons flowing in the oxide semiconductor film 19a are less likely to be captured by the carrier traps because there is a distance between the carrier traps and the oxide semiconductor film 19a. Accordingly, the amount of on-state current of the transistor can be increased, and the field-effect mobility can be increased.
  • the electrons become negative fixed charges. As a result, a threshold voltage of the transistor changes.
  • capture of electrons by the carrier traps can be reduced, and accordingly, the amount of change in the threshold voltage can be reduced.
  • Impurities from the outside can be blocked by the oxide semiconductor film 39a, and accordingly, the amount of impurities that are transferred from the outside to the oxide semiconductor film 19a can be reduced. Furthermore, an oxygen vacancy is less likely to be formed in the oxide semiconductor film 39a. Consequently, the impurity concentration and the number of oxygen vacancies in the oxide semiconductor film 19a can be reduced.
  • the oxide semiconductor films 19a and 39a are not only formed by simply stacking each film, but also are formed to have a continuous junction (here, in particular, a structure in which the energy of the bottom of the conduction band is changed continuously between each film). In other words, a stacked-layer structure in which there exist no impurity that forms a defect level such as a trap center or a recombination center at the interface between the films is provided. If an impurity exists between the oxide semiconductor films 19a and 39a which are stacked, a continuity of the energy band is damaged, and the carrier is captured or recombined at the interface and then disappears.
  • a multi-chamber deposition apparatus including a load lock chamber.
  • Each chamber in the sputtering apparatus is preferably evacuated to be a high vacuum state (to the degree of about 5 x 10 ⁇ 7 Pa to 1 x 10 ⁇ 4 Pa) with an adsorption vacuum evacuation pump such as a cryopump in order to remove water or the like, which serves as an impurity against the oxide semiconductor film, as much as possible.
  • a turbo molecular pump and a cold trap are preferably combined so as to prevent a backflow of a gas, especially a gas containing carbon or hydrogen from an exhaust system to the inside of the chamber.
  • a multilayer film 38a may be provided instead of the multilayer film 37a.
  • a multilayer film 38b may be provided instead of the multilayer film 37b.
  • the multilayer film 38a includes an oxide semiconductor film 49a, the oxide semiconductor film 19a, and the oxide semiconductor film 39a. That is, the multilayer film 38a has a three-layer structure. Furthermore, the oxide semiconductor film 19a functions as a channel region.
  • the oxide semiconductor film 49a can be formed using a material and a formation method similar to those of the oxide semiconductor film 39a.
  • the multilayer film 38b includes an oxide semiconductor film 49b having conductivity, an oxide semiconductor film 19f having conductivity, and an oxide semiconductor film 39b having conductivity. In other words, the multilayer film 38b has a three-layer structure.
  • the multilayer film 38b functions as a pixel electrode.
  • the oxide semiconductor film 49b can be formed using a material and a formation method similar to those of the oxide semiconductor film 39b as appropriate.
  • the oxide insulating film 17 and the oxide semiconductor film 49a are in contact with each other. That is, the oxide semiconductor film 49a is provided between the oxide insulating film 17 and the oxide semiconductor film 19a.
  • the multilayer film 38a and the oxide insulating film 23 are in contact with each other.
  • the oxide semiconductor film 39a and the oxide insulating film 23 are in contact with each other. That is, the oxide semiconductor film 39a is provided between the oxide semiconductor film 19a and the oxide insulating film 23.
  • the thickness of the oxide semiconductor film 49a be smaller than that of the oxide semiconductor film 19a.
  • the thickness of the oxide semiconductor film 49a is greater than or equal to 1 nm and less than or equal to 5 nm, preferably greater than or equal to 1 nm and less than or equal to 3 nm, the amount of change in the threshold voltage of the transistor can be reduced.
  • the oxide semiconductor film 39a is provided between the oxide semiconductor film 19a and the oxide insulating film 23.
  • the oxide semiconductor film 39a is provided between the oxide semiconductor film 19a and the oxide insulating film 23.
  • Impurities from the outside can be blocked by the oxide semiconductor film 39a, and accordingly, the amount of impurities that are transferred from the outside to the oxide semiconductor film 19a can be reduced. Furthermore, an oxygen vacancy is less likely to be formed in the oxide semiconductor film 39a. Consequently, the impurity concentration and the number of oxygen vacancies in the oxide semiconductor film 19a can be reduced.
  • the oxide semiconductor film 49a is provided between the oxide insulating film 17 and the oxide semiconductor film 19a
  • the oxide semiconductor film 39a is provided between the oxide semiconductor film 19a and the oxide insulating film 23.
  • the transistor 102c having such a structure includes very few defects in the multilayer film 38a including the oxide semiconductor film 19a; thus, the electrical characteristics of the transistor can be improved, and typically, the on-state current can be increased and the field-effect mobility can be improved. Moreover, in a BT stress test and a BT photostress test which are examples of a stress test, the amount of change in threshold voltage is small, and thus, reliability is high.

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  • Thin Film Transistor (AREA)
  • Electrodes Of Semiconductors (AREA)
  • Liquid Crystal (AREA)
  • Semiconductor Integrated Circuits (AREA)
  • Metal-Oxide And Bipolar Metal-Oxide Semiconductor Integrated Circuits (AREA)
  • Devices For Indicating Variable Information By Combining Individual Elements (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
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