US20150155313A1 - Semiconductor device - Google Patents

Semiconductor device Download PDF

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US20150155313A1
US20150155313A1 US14/546,443 US201414546443A US2015155313A1 US 20150155313 A1 US20150155313 A1 US 20150155313A1 US 201414546443 A US201414546443 A US 201414546443A US 2015155313 A1 US2015155313 A1 US 2015155313A1
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Prior art keywords
film
oxide semiconductor
conductive film
oxide
semiconductor film
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US14/546,443
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Shunpei Yamazaki
Junichi Koezuka
Yukinori SHIMA
Masami Jintyou
Takashi HAMOCHI
Satoshi HIGANO
Yasuharu Hosaka
Toshimitsu Obonai
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Semiconductor Energy Laboratory Co Ltd
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Semiconductor Energy Laboratory Co Ltd
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Priority to JP2013248284 priority Critical
Priority to JP2013-248284 priority
Priority to JP2014-038615 priority
Priority to JP2014038615 priority
Application filed by Semiconductor Energy Laboratory Co Ltd filed Critical Semiconductor Energy Laboratory Co Ltd
Assigned to SEMICONDUCTOR ENERGY LABORATORY CO., LTD. reassignment SEMICONDUCTOR ENERGY LABORATORY CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HAMOCHI, TAKASHI, HIGANO, SATOSHI, HOSAKA, YASUHARU, JINTYOU, MASAMI, KOEZUKA, JUNICHI, OBONAI, TOSHIMITSU, SHIMA, YUKINORI, YAMAZAKI, SHUNPEI
Publication of US20150155313A1 publication Critical patent/US20150155313A1/en
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/02Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier
    • H01L27/12Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being other than a semiconductor body, e.g. an insulating body
    • H01L27/1214Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being other than a semiconductor body, e.g. an insulating body comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
    • H01L27/1255Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being other than a semiconductor body, e.g. an insulating body comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs integrated with passive devices, e.g. auxiliary capacitors
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/02Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier
    • H01L27/12Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being other than a semiconductor body, e.g. an insulating body
    • H01L27/1214Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being other than a semiconductor body, e.g. an insulating body comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
    • H01L27/124Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being other than a semiconductor body, e.g. an insulating body comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs with a particular composition, shape or layout of the wiring layers specially adapted to the circuit arrangement, e.g. scanning lines in LCD pixel circuits
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L28/00Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
    • H01L28/20Resistors
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L28/00Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
    • H01L28/20Resistors
    • H01L28/24Resistors with an active material comprising a refractory, transition or noble metal, metal compound or metal alloy, e.g. silicides, oxides, nitrides
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L28/00Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
    • H01L28/40Capacitors
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L28/00Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
    • H01L28/40Capacitors
    • H01L28/60Electrodes
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L29/00Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof; Multistep manufacturing processes therefor
    • H01L29/40Electrodes ; Multistep manufacturing processes therefor
    • H01L29/43Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H01L29/45Ohmic electrodes
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L29/00Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof; Multistep manufacturing processes therefor
    • H01L29/66Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76Unipolar devices, e.g. field effect transistors
    • H01L29/772Field effect transistors
    • H01L29/78Field effect transistors with field effect produced by an insulated gate
    • H01L29/786Thin film transistors, i.e. transistors with a channel being at least partly a thin film
    • H01L29/7869Thin film transistors, i.e. transistors with a channel being at least partly a thin film having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L29/00Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof; Multistep manufacturing processes therefor
    • H01L29/66Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76Unipolar devices, e.g. field effect transistors
    • H01L29/772Field effect transistors
    • H01L29/78Field effect transistors with field effect produced by an insulated gate
    • H01L29/786Thin film transistors, i.e. transistors with a channel being at least partly a thin film
    • H01L29/7869Thin film transistors, i.e. transistors with a channel being at least partly a thin film having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
    • H01L29/78693Thin film transistors, i.e. transistors with a channel being at least partly a thin film having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate the semiconducting oxide being amorphous

Abstract

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 including an oxide semiconductor film is provided. The semiconductor device includes an oxide semiconductor film having conductivity on an insulating surface and a conductive film in contact with the oxide semiconductor film having conductivity. The conductive film includes a Cu—X alloy film (X is Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti).

Description

    TECHNICAL FIELD
  • One embodiment of the present invention relates to a semiconductor device and a display device each including an oxide semiconductor.
  • Note that 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. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, 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.
  • BACKGROUND ART
  • There is a trend in a display device using a transistor (e.g., a liquid crystal panel and an organic EL panel) toward a larger screen. As the screen size becomes larger, in the case of a display device using an active element such as a transistor, a voltage applied to an element varies depending on the position of a wiring which is connected to the element due to wiring resistance, which cause a problem of deterioration of display quality such as display unevenness and a defect in grayscale.
  • Conventionally, 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. However, 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. Note that 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).
  • In addition, as an ohmic electrode formed over a semiconductor film containing an oxide semiconductor material including indium, a Cu—Mn alloy has been disclosed (see Patent Document 2).
  • REFERENCE Patent Document
  • [Patent Document 1] Japanese Published Patent Application No. 2007-123861
  • [Patent Document 2] PCT International Publication No. 2012/002573
  • DISCLOSURE OF INVENTION
  • Regarding a transistor in which a silicon-based semiconductor material is used for a semiconductor film, research and development have been extensively conducted on a structure in which a copper film is used for a wiring, a signal line, or the like while copper in the copper film is not diffused into a semiconductor film. However, there has been a problem in that the structure and its manufacturing method are not yet optimized for a transistor using an oxide semiconductor film.
  • Furthermore, 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.
  • In view of the above problems, 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.
  • Note that the descriptions of these objects do not disturb the existence of other objects. In one embodiment of the present invention, there is no need to achieve all the objects. Objects other than the above objects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.
  • 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 (X is 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 8×1019 atoms/cm3. The first conductive film includes a Cu—X alloy film (X is 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 1×10−3 Ωcm and lower than 1×104 Ωcm. The first conductive film includes a Cu—X alloy film (X is Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti).
  • Note that 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.
  • Alternatively, 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. Note that the insulating film may include a nitride insulating film.
  • The first conductive film includes a Cu—Mn alloy film. Alternatively, the first conductive film is a stack of a Cu—Mn alloy film and a Cu film over the Cu—Mn alloy film. Alternatively, 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. In the case where 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—M—Zn oxide (M is Al, Ga, Y, Zr, Sn, La, Ce, or Nd).
  • According to one embodiment of the present invention, 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. According to another embodiment of the present invention, 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. According to another embodiment of the present invention, 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. According to another embodiment of the present invention, a novel semiconductor device of which productivity is improved can be provided. According to another embodiment of the present invention, a novel semiconductor device or a method for manufacturing the novel semiconductor device can be provided.
  • Note that the description of these effects does not disturb the existence of other effects. In one embodiment of the present invention, there is no need to obtain all the effects. Other effects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.
  • BRIEF DESCRIPTION OF DRAWINGS
  • In the accompanying drawings:
  • FIGS. 1A to 1E are cross-sectional views illustrating embodiments of a semiconductor device of the present invention;
  • FIGS. 2A 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. 4A to 4C are cross-sectional views illustrating one embodiment of a method for manufacturing a semiconductor device of the present invention;
  • FIGS. 5A to 5F are cross-sectional views illustrating embodiments of a semiconductor device of the present invention;
  • FIGS. 6A to 6C are cross-sectional views illustrating embodiments of a semiconductor device of the present invention;
  • FIGS. 7A to 7D are cross-sectional views illustrating embodiments of a semiconductor device of the present invention;
  • FIGS. 8A and 8B are circuit diagrams each showing one embodiment of a semiconductor device of the present invention;
  • FIGS. 9A 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. 11A to 11C 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. 20A to 20C are cross-sectional views illustrating one embodiment of a method for manufacturing a display device;
  • FIGS. 21A 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. 26A 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. 29A 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. 38A to 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. 43A to 43C show an InGaZnO4 crystal and a pellet;
  • FIGS. 44A to 44D are schematic views illustrating a deposition model of a CAAC-OS;
  • FIGS. 45A and 45B illustrate an InGaZnO4 crystal;
  • FIGS. 46A and 46B show a structure and the like of InGaZnO4 before collision of an atom;
  • FIGS. 47A and 47B show a structure and the like of InGaZnO4 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. 52A to 52E are each an external view of an electronic device of one embodiment; and
  • FIGS. 53A and 53B show a STEM image of Sample and a result of EDX analysis.
  • BEST MODE FOR CARRYING OUT THE INVENTION
  • Embodiments will be described below with reference to drawings. However, the embodiments can be implemented with various modes. It will be readily appreciated by those skilled in the art that modes and details can be changed in various ways without departing from the spirit and scope of the present invention. Thus, the present invention should not be interpreted as being limited to the following description of the embodiments.
  • In the drawings, the size, the layer thickness, or the region is exaggerated for clarity in some cases. Therefore, embodiments of the present invention are not limited to such a scale. Note that the drawings are schematic views showing ideal examples, and embodiments of the present invention are not limited to shapes or values shown in the drawings.
  • Note that in this specification, ordinal numbers such as “first”, “second”, and “third” are used in order to avoid confusion among components, and the terms do not limit the components numerically.
  • Note that in this specification, terms for describing arrangement, such as “over” “above”, “under”, and “below”, are used for convenience in describing a positional relation between components with reference to drawings. The positional relation between components is changed as appropriate in accordance with a direction in which each component is described. Thus, the positional relation is not limited to that described with a term used in this specification and can be explained with another term as appropriate depending on the situation.
  • In this specification and the like, a transistor is an element having at least three terminals of a gate, a drain, and a source. In addition, 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. Note that in this specification and the like, a channel region refers to a region through which current mainly flows.
  • Furthermore, functions of a source and a drain might be switched when transistors having different polarities are employed or a direction of current flow is changed in circuit operation, for example. Therefore, the terms “source” and “drain” can be switched in this specification and the like.
  • Note that in this specification and the like, the expression “electrically connected” includes the case where components are connected through 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.
  • Embodiment 1
  • In this embodiment, a semiconductor device of one embodiment of the present invention is described with reference to FIGS. 1A to 1E, FIGS. 2A to 2D, FIGS. 3A to 3D, FIGS. 4A to 4C, FIGS. 5A to 5F, and FIGS. 6A to 6C. In this embodiment, 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. Here, the oxide semiconductor film having conductivity serves as an electrode or a wiring.
  • FIGS. 1A to 1E 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.
  • In FIG. 1A, an insulating film 153, an oxide semiconductor film 155 b having conductivity over the insulating film 153, and a conductive film 159 in contact with the oxide semiconductor film 155 b having conductivity are formed over a substrate 151.
  • Furthermore, as illustrated in FIG. 1B, an insulating film 157 may be formed over the insulating film 153, the oxide semiconductor film 155 b having conductivity, and the conductive film 159.
  • Alternatively, as illustrated in FIG. 1C, the oxide semiconductor film 155 b having conductivity may be formed over an insulating film 157 a. In this case, an insulating film 153 a can be provided over the oxide semiconductor film 155 b having conductivity and the conductive film 159.
  • The oxide semiconductor film 155 b 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 155 b having conductivity has a light-transmitting property.
  • In the case where the oxide semiconductor film 155 b having conductivity contains an In—M—Zn oxide film, 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 M is less than 66 atomic %.
  • The energy gap of the oxide semiconductor film 155 b 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 155 b 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.
  • In the case where the oxide semiconductor film 155 b 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. As the atomic ratio of metal elements of such a sputtering target, In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=2:1:1.5, In:M:Zn=2:1:2.3, In:M:Zn=2:1:3, In:M:Zn=3:1:2, or the like is preferable. Note that the proportion of each metal element in the atomic ratio of the formed oxide semiconductor film 155 b having conductivity varies within a range of ±40% of that in the above atomic ratio of the sputtering target as an error.
  • The oxide semiconductor film 155 b 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. Among the non-single crystal structures, the amorphous structure has the highest density of defect levels, whereas the CAAC-OS has the lowest density of defect levels.
  • Note that the oxide semiconductor film 155 b 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. Furthermore, 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 157 a are preferably formed of a film containing hydrogen, typically, a silicon nitride film containing hydrogen. When the insulating films 157 and 157 a in contact with an oxide semiconductor film contain hydrogen, the hydrogen is supplied to the oxide semiconductor film, so that the oxide semiconductor film 155 b having conductivity can be formed.
  • The oxide semiconductor film 155 b having conductivity includes an impurity. Hydrogen is given as an example of the impurity included in the oxide semiconductor film 155 b having conductivity. Instead of hydrogen, as 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 155 b having conductivity is higher than or equal to 8×1019 atoms/cm3, preferably higher than or equal to 1×1020 atoms/cm3, further preferably higher than or equal to 5×1020 atoms/cm3. The hydrogen concentration in the oxide semiconductor film 155 b having conductivity is lower than or equal to 20 atomic %, preferably lower than or equal to 1×1022 atoms/cm3. Note that the concentration of hydrogen in the oxide semiconductor film 155 b is measured by secondary ion mass spectrometry (SIMS) or hydrogen forward scattering (HFS).
  • Including defects and impurities, the oxide semiconductor film 155 b having conductivity exhibits conductivity. The resistivity of the oxide semiconductor film 155 b having conductivity is preferably higher than or equal to 1×10−3 Ωcm and lower than 1×104 Ωcm, further preferably higher than or equal to 1×10−3 Ωcm and lower than 1×10−1 Ωcm.
  • The oxide semiconductor film 155 b having conductivity includes defects in addition to impurities. The oxide semiconductor film 155 b 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. As an example of the defect included in the oxide semiconductor film 155 b having conductivity, an oxygen vacancy is given.
  • 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 155 b 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 (X is Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti) (hereinafter, simply referred to as Cu—X alloy film), and for example, 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. As 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.
  • Here, the conductive film 159 has a stacked-layer structure of a conductive film 159 a in contact with the oxide semiconductor film 155 b having conductivity and a conductive film 159 b in contact with the conductive film 159 a. Furthermore, the Cu—X alloy film is used as the conductive film 159 a and the conductive film including a low-resistance material is used as the conductive film 159 b.
  • The conductive film 159 also serves as a lead wiring or the like. The conductive film 159 includes the conductive film 159 a using the Cu—X alloy film and the conductive film 159 b 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 155 b having conductivity, whereby the adhesion between the oxide semiconductor film 155 b having conductivity and the conductive film 159 can be increased and the contact resistance therebetween can be reduced.
  • Here, FIG. 1D shows an enlarged view of a region where the oxide semiconductor film 155 b having conductivity is in contact with the conductive film 159. When the Cu—X alloy film is used as the conductive film 159 a in contact with the oxide semiconductor film 155 b having conductivity, a coating film 156 is formed at an interface between the oxide semiconductor film 155 b 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 155 b having conductivity or the insulating film 157. As the compound including X oxide including X, nitride including X silicide including X carbide including X and the like are given. As 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. By forming 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 155 b having conductivity can be suppressed.
  • As an example of the conductive film 159 a, a Cu—Mn alloy film is used, whereby the adhesion between the conductive film 159 a and the underlying oxide semiconductor film 155 b 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 155 b having conductivity.
  • As a specific example, 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 155 b having conductivity and the conductive film 159 a. 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 155 b having conductivity. With the coating film 156, the adhesion between the oxide semiconductor film 155 b having conductivity and the conductive film 159 a 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 159 a can obtain high conductivity.
  • Alternatively, as illustrated in FIG. 1E, a coating film 156 a 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 156 a 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 155 b having conductivity or the insulating film 157. As the compound including X, oxide including X nitride including X silicide including X carbide including X and the like are given.
  • In the case where an oxide insulating film is formed as the insulating film 157, in a region where the coating film 156 a is in contact with the conductive film 159 b, an oxide of a low-resistance material is formed. Note that X in the Cu—X alloy film is included in the region where the coating film 156 a is in contact with the conductive film 159 b in some cases. This is probably due to an attachment of a residue generated in the etching of the conductive film 159 a, 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, X in the Cu—X alloy film is oxidized to oxide in some cases.
  • For example, a copper (Cu) film is preferably used as the conductive film 159 b, because the thickness of the conductive film 159 b can be increased to improve the conductivity of the conductive film 159. Here, 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 155 b having conductivity is suppressed and a wiring has high conductivity can be obtained.
  • As the substrate 151, a variety of substrates can be used without particular limitation. Examples of 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. As an example of a glass substrate, a barium borosilicate glass substrate, an aluminoborosilicate glass substrate, a soda lime glass substrate, or the like can be given. 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. Specifically, the use of 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 high current capability. A circuit using such transistors achieves lower power consumption of the circuit or higher integration of the circuit.
  • Furthermore, a flexible substrate may be used as the substrate 151, and a semiconductor element may be formed directly on the flexible substrate. Alternatively, 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. As the above separation layer, 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.
  • As the insulating films 153 and 153 a, 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. Alternatively, the insulating films 153 and 153 a may be formed using a high-k material such as hafnium silicate (HfSiOx), hafnium silicate to which nitrogen is added (HfSixOyNz), hafnium aluminate to which nitrogen is added (HfAlxOyNz), hafnium oxide, or yttrium oxide. Note that in this specification, “silicon oxynitride film” refers to a film that contains more oxygen than nitrogen, and “silicon nitride oxide film” refers to a film that contains more nitrogen than oxygen.
  • Alternatively, the insulating films 153 and 153 a 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.
  • <Formation Method 1 of Oxide Semiconductor Film 155 b Having Conductivity and Conductive Film 159>
  • First of all, a method for forming the oxide semiconductor film 155 b having conductivity and the conductive film 159, which are illustrated in FIG. 1A, is described with reference to FIGS. 2A to 2D.
  • First, the substrate 151 is prepared. Here, a glass substrate is used as the substrate 151.
  • As illustrated in FIG. 2A, 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.
  • 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.
  • As a sputtering gas, a rare gas (typically argon), an oxygen gas, or a mixed gas of a rare gas and an oxygen gas is used as appropriate. In the case of using the mixed gas of a rare gas and an oxygen gas, the proportion of an oxygen gas to a rare gas is preferably increased.
  • Furthermore, a target may be appropriately selected in accordance with the composition of the oxide semiconductor film to be formed.
  • For example, in the case where 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.
  • For the deposition of the CAAC-OS film as the oxide semiconductor film, the following conditions are preferably used.
  • By suppressing entry of impurities into the CAAC-OS film during the deposition, the crystal state can be prevented from being broken by the impurities. For example, the impurity concentration (e.g., hydrogen, water, carbon dioxide, and nitrogen) which exist in the deposition chamber may be reduced. Furthermore, the impurity concentration in a deposition gas may be reduced. Specifically, a deposition gas whose dew point is −80° C. or lower, preferably −100° C. or lower is used.
  • In the case where an oxide semiconductor film, e.g., an In—Ga—Zn—O film is formed using a deposition apparatus employing ALD, an In(CH3)3 gas and an O3 gas are sequentially introduced plural times to form an In—O layer, a Ga(CH3)3 gas and an O3 gas are introduced at a time to form a GaO layer, and then a Zn(CH3)2 gas and an O3 gas are introduced at a time to form a ZnO layer. Note that the order of these layers is not limited to this example. A mixed compound layer such as an In—Ga—O layer, an In—Zn—O layer, or a Ga—Zn—O layer may be formed by mixing of these gases. Note that although an H2O gas which is obtained by bubbling with an inert gas such as Ar may be used instead of an O3 gas, it is preferable to use an O3 gas that does not contain H. Instead of an In(CH3)3 gas, an In(C2H5)3 may be used. Instead of a Ga(CH3)3 gas, a Ga(C2H5)3 gas may be used. Furthermore, a Zn(CH3)2 gas may be used.
  • After that, 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. By the heat treatment, oxygen is released from the oxide semiconductor film 155, so that defects can be formed. As a result, variation in hydrogen concentration in the oxide semiconductor film 155 b 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. With the use of an RTA apparatus, 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. Thus, 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.
  • As 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.
  • As a result, as illustrated in FIG. 2B, an oxide semiconductor film 155 a including defects can be formed.
  • Then, the oxide semiconductor film 155 a 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.
  • Alternatively, after the surface of the oxide semiconductor film 155 a including defects is exposed to a solution including boron, phosphorus, alkali metal, alkaline earth metal, or the like heat treatment is performed.
  • 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. Note that 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.
  • As a result, as illustrated in FIG. 2C, the oxide semiconductor film 155 b having conductivity can be formed. The oxide semiconductor film 155 b having conductivity includes defects and impurities. By the effect of the defects and the impurities, the conductivity of the oxide semiconductor film 155 b having conductivity is increased as compared to that of the oxide semiconductor film 155. As an example of the action of defects and impurities, hydrogen enters an oxygen vacancy, whereby an electron serving as a carrier is generated. Alternatively, bonding of part of hydrogen to oxygen bonded to a metal atom causes generation of an electron serving as a carrier. By these actions, the conductivity of the oxide semiconductor film is increased. As a result, the oxide semiconductor film 155 b having conductivity serves as an electrode or a wiring. Furthermore, the oxide semiconductor film 155 b having conductivity has a light-transmitting property. Thus, a light-transmitting electrode or a light-transmitting wiring can be formed.
  • Note that the resistivity of the oxide semiconductor film 155 b having conductivity is higher than that of the conductive film 159. Thus, as a lead wiring, the conductive film 159 is preferably in contact with the oxide semiconductor film 155 b.
  • Next, as illustrated in FIG. 2D, the conductive film 159 is formed over the oxide semiconductor film 155 b having conductivity. Here, after a stack of the Cu—X alloy film and the conductive film including a low-resistance material is formed, 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 159 a formed of the Cu—X alloy film and the conductive film 159 b formed of the conductive film including a low-resistance material are stacked can be formed.
  • As a method for etching the Cu—X alloy film and the conductive film including a low-resistance material, a dry etching method or a wet etching method can be used as appropriate. In the case where a copper (Cu) film is used as the conductive film including a low-resistance material, 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 159 a formed of the Cu—X alloy film and the conductive film 159 b formed of the conductive film including a low-resistance material are stacked can be formed in a single wet etching step. As an etchant used in the wet etching method, an etchant containing an organic acid solution and hydrogen peroxide water, or the like is used.
  • Through the above steps, the oxide semiconductor film having conductivity and the conductive film in contact with the oxide semiconductor film having conductivity can be formed.
  • <Formation Method 2 of Oxide Semiconductor Film 155 b Having Conductivity and Conductive Film 159>
  • A formation method of the oxide semiconductor film 155 b having conductivity which is different from the method in FIGS. 2A to 2D is described with reference to FIGS. 3A to 3D.
  • As illustrated in FIG. 3A, 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 155 a including defects can be obtained as illustrated in FIG. 3B. Note that a typical example of the defects included in the oxide semiconductor film 155 a 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. By performing heat treatment at 350° C. or higher, oxygen is released from the oxide semiconductor film. In addition, by performing heat treatment at 800° C. or lower, oxygen can be released from the oxide semiconductor film while the crystal structure of the oxide semiconductor film is maintained. Moreover, heating is preferably performed in vacuum, typically under a pressure higher than or equal to 1×10−7 Pa and lower than or equal to 10 Pa, preferably higher than or equal to 1×10−7 Pa and lower than or equal to 1 Pa, further preferably higher than or equal to 1×10−7 Pa and lower than or equal to 1E−1 Pa.
  • Next, by a method similar to that in FIG. 2B, the oxide semiconductor film 155 a 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.
  • Alternatively, after the surface of the oxide semiconductor film 155 a including defects is exposed to a solution including boron, phosphorus, alkali metal, or alkaline earth metal, heat treatment is performed.
  • As a result, as illustrated in FIG. 3C, the oxide semiconductor film 155 b having conductivity can be formed.
  • Next, by a method similar to that in FIG. 2D, the conductive film 159 can be formed over the oxide semiconductor film 155 b having conductivity (see FIG. 3D).
  • <Formation Method 3 of Oxide Semiconductor Film 155 b Having Conductivity and Conductive Film 159>
  • A formation method of the oxide semiconductor film 155 b having conductivity which is different from the methods in FIGS. 2A to 2D and FIGS. 3A to 3D is described with reference to FIGS. 4A to 4C.
  • As illustrated in FIG. 4A, after the insulating film 153 is formed over the substrate 151, the oxide semiconductor film 155 is formed over the insulating film 153.
  • Next, by a method similar to that in FIG. 2D, the conductive film 159 is formed over the oxide semiconductor film 155 (see FIG. 4B). Here, as the conductive film 159, the conductive film 159 a and the conductive film 159 b are formed.
  • Next, 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.
  • By using a sputtering method, a plasma CVD method, or the like as a formation method of the insulating film 157, 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 155 b having conductivity can be formed. By the action of defects and impurities, the conductivity of the oxide semiconductor film 155 b having conductivity is increased as compared to that of the oxide semiconductor film 155. Thus, the oxide semiconductor film 155 b having conductivity serves as an electrode or a wiring.
  • Modification Example 1
  • Modification examples of the conductive film 159 are described with reference to FIGS. 5A to 5F. Here, modification examples of the conductive film 159 in FIG. 1B are shown; however, the modification examples can be used in the conductive film 159 in FIGS. 1A and 1C as appropriate.
  • As illustrated in FIG. 5A, the conductive film 159 a can be formed of a single layer of the Cu—X alloy film over the oxide semiconductor film 155 b having conductivity.
  • Alternatively, as illustrated in FIG. 5B, the conductive film 159 can be formed over the oxide semiconductor film 155 b having conductivity by stacking the conductive film 159 a formed of the Cu—X alloy film, the conductive film 159 b formed of the conductive film including a low-resistance material, and a conductive film 159 c formed of the Cu—X alloy film.
  • When the conductive film 159 includes the conductive film 159 c formed of the Cu—X alloy film over the conductive film 159 b formed of the conductive film including a low-resistance material, the conductive film 159 c formed of the Cu—X alloy film serves as a protective film of the conductive film 159 b including a low-resistance material; thus, the reaction of the conductive film 159 b including a low-resistance material in the formation of the insulating film 157 can be prevented.
  • Alternatively, as illustrated in FIGS. 5C and 5D, the oxide semiconductor film 155 b having conductivity may be formed over the insulating film 157 a formed of a film including hydrogen. In this case, the insulating film 153 a can be provided over the oxide semiconductor film 155 b having conductivity and the conductive film 159.
  • Next, FIGS. 5E and 5F show enlarged views of regions where the oxide semiconductor film 155 b having conductivity is in contact with the conductive film 159 and the conductive film 159 a respectively. As illustrated in FIG. 5E, a coating film 156 b is formed on at least one of the bottom surface, side surface, and top surface of the conductive film 159 a, preferably on the outer periphery of the conductive film 159 a in some cases. The coating film 156 b 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 a and an element included in the oxide semiconductor film 155 b having conductivity or the insulating film 157. As the compound including X oxide including X nitride including X silicide including X carbide including X and the like are given.
  • In the case where a Cu—Mn alloy film is used as the Cu—X alloy film, as an example of the coating film 156 b, a manganese oxide film is formed.
  • Alternatively, as illustrated in FIG. 5F, a coating film 156 c 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 156 c 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 155 b having conductivity or the insulating film 157. In a region where the coating film 156 c is in contact with the conductive film 159 b, an oxide of the low-resistance material is formed. Furthermore, X in the Cu—X alloy film is included in the region where the coating film 156 c is in contact with the conductive film 159 b in some cases. This is probably due to an attachment of a residue generated in the etching of the conductive film 159 a or the conductive film 159 c, 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, X in 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 159 b, as an example of the coating film 156 c, a manganese oxide film is formed.
  • Modification Example 2
  • Here, modification examples of the oxide semiconductor film having conductivity and the conductive film are described with reference to FIGS. 6A to 6C.
  • In FIG. 6A, a single layer of the conductive film 159 a formed of the Cu—X alloy film is provided between the insulating film 153 and the oxide semiconductor film 155 b having conductivity.
  • Alternatively, as illustrated in FIG. 6B, the conductive film 159 having a two-layer structure is provided between the insulating film 153 and the oxide semiconductor film 155 b having conductivity. The conductive film 159 is formed by stacking the conductive film 159 a formed of the Cu—X alloy film and the conductive film 159 b formed of the conductive film including a low-resistance material.
  • Alternatively, as illustrated in FIG. 6C, the conductive film 159 having a three-layer structure is provided between the insulating film 153 and the oxide semiconductor film 155 b having conductivity. The conductive film 159 is formed by stacking the conductive film 159 a formed of the Cu—X alloy film, the conductive film 159 b formed of the conductive film including a low-resistance material, and the conductive film 159 c formed of the Cu—X alloy film.
  • When the conductive film 159 c formed of the Cu—X alloy film is provided over the conductive film 159 b formed of the conductive film including a low-resistance material in the conductive film 159, the conductive film 159 c formed of the Cu—X alloy film serves as a protective film of the conductive film 159 b including a low-resistance material; thus, the reaction of the conductive film 159 b including a low-resistance material in the formation of the oxide semiconductor film 155 b having conductivity can be prevented.
  • The structures, methods, and the like described in this embodiment can be used as appropriate in combination with any of the structures, methods, and the like described in the other embodiments.
  • Embodiment 2
  • In this embodiment, 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. 10A and 10B, and FIGS. 11A to 11C.
  • FIGS. 7A to 7D are cross-sectional views of resistors included in a semiconductor device.
  • A resistor 160 a in FIG. 7A includes the oxide semiconductor film 155 b having conductivity and a pair of conductive films 161 and 162 in contact with the oxide semiconductor film 155 b having conductivity. The oxide semiconductor film 155 b having conductivity and the pair of conductive films 161 and 162 are provided over the insulating film 153 formed over the substrate 151.
  • Furthermore, 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.
  • In the resistor 160 a in FIG. 7A, the conductive film 161 has a stacked-layer structure of a conductive film 161 a in contact with the oxide semiconductor film 155 b having conductivity and a conductive film 161 b in contact with the conductive film 161 a, and the conductive film 162 has a stacked-layer structure of a conductive film 162 a in contact with the oxide semiconductor film 155 b having conductivity and a conductive film 162 b in contact with the conductive film 162 a.
  • Here, as the conductive films 161 a and 162 a, the Cu—X alloy film is used. As the conductive films 161 b and 162 b, the conductive film including a low-resistance material is used.
  • Furthermore, as in a resistor 160 b illustrated in FIG. 7B, the insulating film 157 made of a film including hydrogen may be formed over the insulating film 153, the oxide semiconductor film 155 b having conductivity, and the pair of conductive films 161 and 162.
  • Alternatively, as in a resistor 160 c illustrated in FIG. 7C, the oxide semiconductor film 155 b having conductivity and the pair of conductive films 161 and 162 may be formed over the insulating film 157 a made of a film including hydrogen. In this case, the insulating film 153 a can be provided over the oxide semiconductor film 155 b having conductivity and the pair of conductive films 161 and 162.
  • The resistivity of the oxide semiconductor film 155 b having conductivity is higher than those of the pair of conductive films 161 and 162 including the Cu—X film. Thus, by providing the oxide semiconductor film 155 b having conductivity between the pair of conductive films 161 and 162, they serve as a resistor.
  • The oxide semiconductor film 155 b having conductivity includes defects and impurities. By the effect of the defects and the impurities, the conductivity of the oxide semiconductor film 155 b having conductivity is increased. Furthermore, the oxide semiconductor film 155 b 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 155 b having conductivity, whereby the adhesion between the oxide semiconductor film 155 b having conductivity and the pair of conductive films 161 and 162 can be increased and the contact resistance therebetween can be reduced.
  • Here, FIG. 7D shows an enlarged view of a region where the oxide semiconductor film 155 b having conductivity is in contact with the conductive film 161. When the Cu—X alloy film is used as the conductive film 161 a in contact with the oxide semiconductor film 155 b having conductivity, the coating film 156 including X in the Cu—X alloy film is formed at an interface between the oxide semiconductor film 155 b having conductivity and the conductive film 161 a in some cases. By forming 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 155 b having conductivity can be suppressed.
  • Furthermore, although not illustrated, a coating film such as the coating film 156 a 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.
  • <Circuit Diagram of Protection Circuit>
  • A protection circuit using the resistor in this embodiment is described with reference to FIGS. 8A and 8B. Although a display device is used as a semiconductor device here, a protection circuit can be used in another semiconductor device.
  • FIG. 8A illustrates a specific example of a protection circuit 170 a included in the semiconductor device.
  • The protection circuit 170 a illustrated in FIG. 8A 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 GND) of a power supply line for supplying power to a gate driver or a source driver. Alternatively, the wiring 172 is a wiring that is supplied with a common potential (common line).
  • For example, 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.
  • Although the resistor 173 illustrated in FIG. 8A 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.
  • Next, FIG. 8B illustrates a protection circuit including a plurality of transistors and a plurality of resistors.
  • A protection circuit 170 b illustrated in FIG. 8B includes transistors 174 a, 174 b, 174 c, and 174 d and resistors 173 a, 173 b, and 173 c. The protection circuit 170 b 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. In addition, a first terminal serving as a source electrode of the transistor 174 a is connected to a second terminal serving as a gate electrode of the transistor 174 a, and a third terminal serving as a drain electrode of the transistor 174 a is connected to a wiring 177. A first terminal serving as a source electrode of the transistor 174 b is connected to a second terminal serving as a gate electrode of the transistor 174 b, and a third terminal serving as a drain electrode of the transistor 174 b is connected to the first terminal of the transistor 174 a. A first terminal serving as a source electrode of the transistor 174 c is connected to a second terminal serving as a gate electrode of the transistor 174 c, and a third terminal serving as a drain electrode of the transistor 174 c is connected to the first terminal of the transistor 174 b. A first terminal serving as a source electrode of the transistor 174 d is connected to a second terminal serving as a gate electrode of the transistor 174 d, and a third terminal serving as a drain electrode of the transistor 174 d is connected to the first terminal of the transistor 174 c. In addition, the resistors 173 a and 173 c are provided in the wiring 177. The resistor 173 b is provided between the wiring 176 and the first terminal of the transistor 174 b and the third terminal of the transistor 174 c.
  • Note that 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.
  • The resistor in this embodiment can be used as the resistors in FIGS. 8A and 8B. By appropriately adjusting the shape, specifically the length or the width, of the oxide semiconductor film having conductivity included in the resistor, the resistor can have a given resistance. FIGS. 9A and 9B illustrate an example of a resistor 160 d. FIG. 9A is a top view of the resistor 160 d, and FIG. 9B is a cross-sectional view taken along dashed-dotted line A-B in FIG. 9A. As in the resistor 160 d illustrated in FIGS. 9A and 9B, the top surface of an oxide semiconductor film 155 c having conductivity has a zigzag shape, whereby the resistance of the resistor can be controlled.
  • In this manner, the protection circuit 170 b includes the plurality of transistors that are diode-connected and the plurality of resistors. In other words, the protection circuit 170 b can include diode-connected transistors and resistors that are combined in parallel.
  • With the protection circuit, 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.
  • Furthermore, because 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.
  • The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.
  • Modification Example 1
  • As in a resistor 160 e illustrated in FIG. 10A, each of the conductive films 161 a and 162 a can be formed of a single layer of the Cu—X alloy film over the oxide semiconductor film 155 b having conductivity.
  • Alternatively, as in a resistor 160 f illustrated in FIG. 10B, 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 161 a in contact with the oxide semiconductor film 155 b having conductivity, the conductive film 161 b in contact with the conductive film 161 a, and a conductive film 161 c in contact with the conductive film 161 b. The conductive film 162 has a stacked-layer structure of the conductive film 162 a in contact with the oxide semiconductor film 155 b having conductivity, the conductive film 162 b in contact with the conductive film 162 a, and a conductive film 162 c in contact with the conductive film 162 b.
  • When the pair of conductive films 161 and 162 includes the conductive films 161 c and 162 c formed of the Cu—X alloy film over the conductive films 161 b and 162 b formed of the conductive film including a low-resistance material, the conductive films 161 c and 162 c formed of the Cu—X alloy film serve as protective films of the conductive films 161 b and 162 b including a low-resistance material; thus, the reaction of the conductive films 161 b and 162 b including a low-resistance material in the formation of the insulating film 157 can be prevented.
  • Furthermore, although not illustrated, a coating film such as the coating films 156 b and 156 c 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.
  • Modification Example 2
  • Here, a modification example of a resistor is described with reference to FIGS. 11A to 11C.
  • A resistor 160 g in FIG. 11A includes the pair of conductive films 163 a and 164 a formed of the single-layer Cu—X alloy film between the insulating film 153 and the oxide semiconductor film 155 b having conductivity.
  • Alternatively, as illustrated in FIG. 11B, in a resistor 160 h, the pair of conductive films 163 and 164 is provided between the insulating film 153 and the oxide semiconductor film 155 b having conductivity and has a two-layer structure. The conductive film 163 is formed by stacking the conductive film 163 a formed of the Cu—X alloy film and the conductive film 163 b formed of the conductive film including a low-resistance material. The conductive film 164 is formed by stacking the conductive film 164 a formed of the Cu—X alloy film and the conductive film 164 b formed of the conductive film including a low-resistance material.
  • Alternatively, as illustrated in FIG. 11C, in a resistor 160 i, the pair of conductive films 163 and 164 is provided between the insulating film 153 and the oxide semiconductor film 155 b having conductivity and has a three-layer structure. The conductive film 163 is formed by stacking the conductive film 163 a formed of the Cu—X alloy film, the conductive film 163 b formed of the conductive film including a low-resistance material, and the conductive film 163 c formed of the Cu—X alloy film. The conductive film 164 is formed by stacking the conductive film 164 a formed of the Cu—X alloy film, the conductive film 164 b formed of the conductive film including a low-resistance material, and the conductive film 164 c formed of the Cu—X alloy film.
  • When the conductive films 163 c and 164 c formed of the Cu—X alloy film are provided over the conductive films 163 b and 164 b formed of the conductive film including a low-resistance material in the pair of conductive films 163 and 164, the conductive films 163 c and 164 c formed of the Cu—X alloy film serve as protective films of the conductive films 163 b and 164 b formed of a conductive film including a low-resistance material; thus, the reaction of the conductive films 163 b and 164 b including a low-resistance material in the formation of the oxide semiconductor film 155 b having conductivity and the insulating film 157 can be prevented.
  • Furthermore, although not illustrated, a coating film such as the coating films 156, 156 a, 156 b and 156 c 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.
  • The structures, methods, and the like described in this embodiment can be used as appropriate in combination with any of the structures, methods, and the like described in the other embodiments.
  • Embodiment 3
  • In this embodiment, a capacitor including the oxide semiconductor film having conductivity in Embodiment 1 is described with reference to FIGS. 12A to 12C, FIGS. 13A and 13B, and FIGS. 14A to 14C.
  • FIGS. 12A to 12C are cross-sectional views of capacitors included in a semiconductor device.
  • A capacitor 180 a in FIG. 12A includes the oxide semiconductor film 155 b having conductivity, the insulating film 157 in contact with the oxide semiconductor film 155 b having conductivity, and a conductive film 181 overlapping with the oxide semiconductor film 155 b with the insulating film 157 therebetween. Furthermore, a conductive film serving as a lead wiring may be in contact with the oxide semiconductor film 155 b having conductivity or the conductive film 181. Here, the conductive film 159 in contact with the oxide semiconductor film 155 b having conductivity is the film serving as a lead wiring. The oxide semiconductor film 155 b having conductivity, the insulating film 157, and the conductive film 159 are provided over the insulating film 153 formed over the substrate 151.
  • Furthermore, 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.
  • In the capacitor 180 a in FIG. 12A, the conductive film 159 has a stacked-layer structure of a conductive film 159 a in contact with the oxide semiconductor film 155 b having conductivity and a conductive film 159 b in contact with the conductive film 159 a. As the conductive film 159 a, the Cu—X alloy film is used. As the conductive film 159 b, the conductive film including a low-resistance material is used.
  • Alternatively, as in a capacitor 180 b illustrated in FIG. 12B, the oxide semiconductor film 155 b having conductivity and the conductive film 159 may be formed over the insulating film 157 a. In this case, the insulating film 153 a can be provided between the oxide semiconductor film 155 b 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. For example, a single-layer structure of an aluminum film containing silicon; a single-layer structure of a copper film containing manganese; a two-layer structure in which an aluminum film is stacked over a titanium film; a two-layer structure in which an aluminum film is stacked over a tungsten film; a two-layer structure in which a copper film is stacked over a copper-magnesium-aluminum alloy 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 tungsten film; a two-layer structure in which a copper film is stacked over a copper film containing manganese; a three-layer structure in which a titanium film or a titanium nitride film, an aluminum film or a copper film, and a titanium film or a titanium nitride film are stacked in this order; a three-layer structure in which a molybdenum film or a molybdenum nitride film, an aluminum film or a copper film, and a molybdenum film or a molybdenum nitride film are stacked in this order; a three-layer structure in which a copper film containing manganese, a copper film, and a copper film containing manganese are stacked in this order; and the like can be given.
  • For the conductive film 181, a structure and a material similar to those of the conductive film 159 can be used as appropriate.
  • Furthermore, as the conductive film 181, a light-transmitting conductive film can be used. As the 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 155 b having conductivity includes defects and impurities. By the action of the defects and the impurities, the conductivity of the oxide semiconductor film 155 b having conductivity is increased. Furthermore, the oxide semiconductor film 155 b 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 155 b having conductivity, whereby the adhesion between the oxide semiconductor film 155 b having conductivity and the conductive film 159 can be increased and the contact resistance between them can be reduced.
  • Here, FIG. 12C shows an enlarged view of a region where the oxide semiconductor film 155 b having conductivity is in contact with the conductive film 159. When the Cu—X alloy film is used as the conductive film 159 a in contact with the oxide semiconductor film 155 b having conductivity, the coating film 156 including X in the Cu—X alloy film is formed at an interface between the oxide semiconductor film 155 b having conductivity and the conductive film 159 a in some cases. By forming 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 155 b having conductivity can be suppressed.
  • Furthermore, although not illustrated, a coating film such as the coating film 156 a 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.
  • Modification Example 1
  • As in a capacitor 180 c illustrated in FIG. 13A, a single layer of the conductive film 159 a formed of the Cu—X alloy film can be formed over the oxide semiconductor film 155 b having conductivity.
  • Alternatively, as in a capacitor 180 d illustrated in FIG. 13B, the conductive film 159 can have a three-layer structure. The conductive film 159 has a stacked-layer structure of the conductive film 159 a in contact with the oxide semiconductor film 155 b having conductivity, the conductive film 159 b in contact with the conductive film 159 a, and the conductive film 159 c in contact with the conductive film 159 b.
  • When the conductive film 159 c formed of the Cu—X alloy film is provided over the conductive film 159 b formed of the conductive film including a low-resistance material in the conductive film 159, the conductive film 159 c formed of the Cu—X alloy film serves as a protective film of the conductive film 159 b including a low-resistance material; thus, the reaction of the conductive film 159 b including a low-resistance material in the formation of the insulating film 157 can be prevented.
  • Furthermore, although not illustrated, a coating film such as the coating films 156 b and 156 c 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.
  • Modification Example 2
  • Here, a modification example of a capacitor is described with reference to FIGS. 14A to 14C.
  • A capacitor 180 e in FIG. 14A includes the conductive film 159 a formed of the single-layer Cu—X alloy film between the insulating film 153 and the oxide semiconductor film 155 b having conductivity.
  • Alternatively, as illustrated in FIG. 14B, in a capacitor 180 f, the conductive film 159 is provided between the insulating film 153 and the oxide semiconductor film 155 b having conductivity and has a two-layer structure. The conductive film 159 is formed by stacking the conductive film 159 a formed of the Cu—X alloy film and the conductive film 159 b formed of the conductive film including a low-resistance material.
  • Alternatively, as illustrated in FIG. 14C, in a capacitor 180 g, the conductive film 159 is provided between the insulating film 153 and the oxide semiconductor film 155 b having conductivity and has a three-layer structure. The conductive film 159 is formed by stacking the conductive film 159 a formed of the Cu—X alloy film, the conductive film 159 b formed of the conductive film including a low-resistance material, and the conductive film 159 c formed of the Cu—X alloy film.
  • When the conductive film 159 c formed of the Cu—X alloy film is provided over the conductive film 159 b formed of the conductive film including a low-resistance material in the conductive film 159, the conductive film 159 c formed of the Cu—X alloy film serves as a protective film of the conductive film 159 b including a low-resistance material; thus, the reaction of the conductive film 159 b including a low-resistance material in the formation of the oxide semiconductor film 155 b having conductivity and the insulating film 157 can be prevented.
  • Furthermore, although not illustrated, a coating film such as the coating films 156, 156 a, 156 b and 156 c 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.
  • The structures, methods, and the like described in this embodiment can be used as appropriate in combination with any of the structures, methods, and the like described in the other embodiments.
  • Embodiment 4
  • In this embodiment, a display device of one embodiment of the present invention is described with reference to drawings. 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. 21A 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. Furthermore, 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.
  • In addition, 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. Note that 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.
  • In the case where FFS driving is used for a liquid crystal display device, the capacitor line is not provided and a common line or a common electrode serves as a capacitor line.
  • Note that here, 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. In the case of a liquid crystal display device, 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. 15A.
  • 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. Furthermore, 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.
  • As examples of a driving method of the display device including the liquid crystal element 121, 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. Note that one embodiment of the present invention is not limited to this, and various liquid crystal elements and driving methods can be used as a liquid crystal element and a driving method thereof.
  • 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.
  • In the structure of the pixel 103 illustrated in FIG. 15B, 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.
  • In the pixel 103 in FIG. 15B, 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