Semiconductor device and electronic device

To provide a highly reliable semiconductor device that is suitable for miniaturization and higher density. A semiconductor device includes a first electrode including a protruding portion, a first insulator over the protruding portion, a second insulator covering the first electrode and the first insulator, and a second electrode over the second insulator. The second electrode includes a first region which overlaps with the first electrode with the first insulator and the second insulator provided therebetween and a second region which overlaps with the first electrode with the second insulator provided therebetween. The peripheral portion of the second electrode is provided in the first region.

TECHNICAL FIELD

One embodiment of the present invention relates to a capacitor and a semiconductor device including the capacitor.

In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A semiconductor element such as a transistor, a semiconductor circuit, an arithmetic device, and a memory device are embodiments of a semiconductor device. An imaging device, a display device, a liquid crystal display device, a light-emitting device, an electro-optical device, a power generation device (including a thin film solar cell, an organic thin film solar cell, and the like), and an electronic device may each include a semiconductor device.

BACKGROUND ART

A technique in which a transistor is formed using a semiconductor material has attracted attention. The transistor is applied to a wide range of electronic devices, such as integrated circuits (ICs) or image display devices (also simply referred to as display devices). A silicon-based semiconductor material is widely known as a semiconductor material applicable to the transistor. As another material, an oxide semiconductor has attracted attention.

For example, a technique in which a transistor is formed using zinc oxide or an In—Ga—Zn-based oxide as an oxide semiconductor is disclosed (see Patent Documents 1 and 2).

In addition, in recent years, a demand for an integrated circuit in which semiconductor elements, such as miniaturized transistors, are integrated with high density has grown, with increased performance and reductions in size and weight of electronic devices. For example, a tri-gate transistor and a capacitor-over-bitline (COB) MIM capacitor are reported (Non-Patent Document 1).

REFERENCE

Patent Document

DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to provide a semiconductor device that is suitable for miniaturization and higher density.

Another object of one embodiment of the present invention is to provide a semiconductor device with favorable electrical characteristics. Another object of one embodiment of the present invention is to provide a highly reliable semiconductor device. Another object of one embodiment of the present invention is to provide a semiconductor device with a novel structure.

Note that the description of these objects does not disturb the existence of other objects. In one embodiment of the present invention, there is no need to achieve all the objects. Other 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 includes a first electrode including a protruding portion, a first insulator over the protruding portion, a second insulator covering the first electrode and the first insulator, and a second electrode over the second insulator. The peripheral portion of the second electrode includes a region which overlaps with the first electrode with the first insulator and the second insulator provided therebetween.

Note that “peripheral portion” means a region including an edge along the side surface of an object. In particular, in the structure including a capacitor in this specification, the “peripheral portion” means a region at the edge of an object, which can generate leakage current (edge leakage current). For example, the peripheral portion of the second electrode means a region including an edge of the second electrode. Between the region and the first electrode, leakage current can be generated.

One embodiment of the present invention includes a first electrode including a protruding portion, a first insulator over the protruding portion, a second insulator covering the first electrode and the first insulator, and a second electrode over the second insulator. The second electrode includes a first region which overlaps with the first electrode with the first insulator and the second insulator provided therebetween and a second region which overlaps with the first electrode with the second insulator provided therebetween. The peripheral portion of the second electrode is provided in the first region.

In the above structure, the first electrode is electrically connected to a transistor.

In the above structure, the transistor includes a third electrode, and the third electrode is provided in a conductor that is also used for the first electrode.

One embodiment of the present invention is an electronic device including the above structure and at least one of a display device, a microphone, a speaker, an operation key, a touch panel, and an antenna.

In accordance with one embodiment of the present invention, a semiconductor device that is suitable for miniaturization and higher density can be provided.

In addition, a semiconductor device with favorable electrical characteristics can be provided. In addition, a highly reliable semiconductor device can be provided. In addition, a semiconductor device with a novel structure can be provided. Note that the description of these effects does not disturb the existence of other effects. One embodiment of the present invention does not necessarily achieve all the effects listed above. Other effects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to the drawings. Note that the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details thereof can be variously changed without departing from the spirit and the scope of the present invention. Accordingly, the present invention should not be interpreted as being limited to the content of the embodiments below.

In the structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and repetitive description thereof will be omitted. Furthermore, the same hatching pattern is applied to portions having similar functions, and the portions are not especially denoted by reference numerals in some cases.

In each drawing described in this specification, the size, the layer thickness, or the region of each component is exaggerated for clarity in some cases. Therefore, embodiments of the present invention are not limited to such a scale.

In this specification and the like, ordinal numbers, such as “first” and “second”, are used in order to avoid confusion among components and do not limit the components numerically.

A transistor is a kind of semiconductor element and can achieve amplification of current or voltage, the switching operation for controlling conduction or non-conduction, and the like. A transistor in this specification includes an insulated-gate field-effect transistor (IGFET) and a thin film transistor (TFT).

FIG. 1Ais an example of a top view of a capacitor300.FIG. 1Bis a cross-sectional view along dashed-dotted line A-B inFIG. 1A.

The capacitor300is provided over an insulating film301and includes a first electrode302including conductive layers302aand302b, a barrier layer303, an insulator304, and a second electrode305.

The conductive layers302aand302bcan each be formed using a conductive material, such as a metal material, an alloy material, or a metal oxide material. It is preferable to use a high-melting-point material which has both heat resistance and conductivity, such as tungsten or molybdenum, and it is particularly preferable to use tungsten. The conductive layers302aand302bmay be formed using the same material or different materials from each other.

The conductive layer302bis formed over the conductive layer302asuch that part of the conductive layer302ais exposed; in such a manner, the first electrode302has unevenness on its surface. Although the first electrode302having unevenness is formed using the conductive layers302aand302b, it may be formed by patterning one conductive layer or three or more conductive layers that are stacked. What is needed is that the conductive layer302bis at least provided in a region that overlaps with the peripheral portion of the second electrode305, and an optimal shape of the conductive layer302bmay be designed as appropriate. For example,FIGS. 1A and 1Billustrate an example in which the conductive layer302bhas a quadrangular island shape having an opening; however, the conductive layer302bmay have a polygonal or circular shape.

The barrier layer303is provided over the conductive layer302b. With the barrier layer303, the capacitor300can have fewer defects in shape. As the barrier layer303, an insulating film, such as a silicon oxide film or a gallium oxide film, or a semiconductor film, such as an oxide semiconductor film, can be used.

The insulator304is provided so as to cover the conductive layers302aand302band the barrier layer303. The insulator304can be formed to have a single-layer structure or a stacked-layer structure using, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminum nitride, or the like.

The second electrode305is provided over the first electrode302with the barrier layer303and the insulator304provided therebetween. The second electrode305can be formed using a conductive material, such as a metal material, an alloy material, or a metal oxide material. It is preferable to use a high-melting-point material which has both heat resistance and conductivity, such as tungsten or molybdenum, and it is particularly preferable to use tungsten.

Note that the second electrode305is provided such that its peripheral portion overlaps with the conductive layer302bwith the barrier layer303and the insulator304provided therebetween.

In the capacitor300, the peripheral portion of the second electrode305overlaps with the conductive layer302bwith the barrier layer303provided therebetween. Therefore, in the peripheral portion, the distance between the second electrode305and the first electrode302is longer than that in other regions by at least the thickness of the barrier layer303. This allows the capacitor300of one embodiment of the present invention to have fewer defects in shape and to be highly reliable.

With the first electrode302having unevenness, the capacitor300can be three-dimensional. Accordingly, the capacitance of the capacitor per projected area can be increased, leading to a smaller area, higher integration, and miniaturization of a semiconductor device.

The above is the description of the structural example.

As an application example of this embodiment, a plurality of capacitors300can be stacked as illustrated inFIGS. 2A and 2B. The capacitors300are connected in parallel inFIG. 2A, whereas the capacitors300are connected in series inFIG. 2B. Although two capacitors300are stacked inFIGS. 2A and 2B, three or more capacitors300can be stacked as necessary.

With the above structure, a three-dimensional capacitor can be formed. Accordingly, the capacitance of the capacitor per projected area can be increased, leading to a smaller area, higher integration, and miniaturization of a semiconductor device.

As a modification example of this embodiment, as illustrated inFIGS. 3A and 3B, a protruding portion formed using the conductive layer302bmay also be provided in a groove of the first electrode302of the capacitor300. An optimal shape of the protruding portion may be designed as appropriate. For example, in addition to a stripe (grid) shape, a truncated quadrangular pyramid shape, a truncated polygonal pyramid shape, a truncated conical shape, a polygonal prism shape, or a cylinder shape may be used as long as it is an island shape. In addition, the protruding portion is not necessarily arranged regularly and may be arranged irregularly.

With the protruding portion, the capacitance of the capacitor per projected area can be further increased, leading to a smaller area, higher integration, and miniaturization of a semiconductor device.

[Example of Manufacturing Method]

An example of a method for manufacturing the capacitor illustrated inFIGS. 3A and 3Bwill be described below with reference toFIGS. 4A to 4E,FIGS. 5A to 5D, andFIGS. 6A to 6D.

First, a conductive film302A is formed over the insulating film301(FIG. 4A). The insulating film301can be formed to have a single-layer structure or a stacked-layer structure using, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminum nitride, or the like. The insulating film301can be formed by a sputtering method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), an MBE method, an ALD method, a PLD method, or the like. In particular, it is preferable that the insulating film301be formed by a CVD method, more preferably, a plasma CVD method because coverage can be improved. It is preferable to use a thermal CVD method, an MOCVD method, or an ALD method in order to reduce plasma damage.

It is preferable that the conductive film302A be formed using a metal selected from tantalum, tungsten, titanium, molybdenum, chromium, niobium, and the like, or an alloy material or a compound material containing any of the metals as its main component. Alternatively, polycrystalline silicon to which an impurity, such as phosphorus, is added can be used. Alternatively, a stacked-layer structure including a metal nitride film and a film of any of the above metals may be used. As a metal nitride, tungsten nitride, molybdenum nitride, or titanium nitride can be used. When the metal nitride film is provided, adhesiveness of the metal film can be increased; thus, separation can be prevented.

The conductive film302A can be formed by a sputtering method, an evaporation method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), or the like. It is preferable to use a thermal CVD method, an MOCVD method, or an ALD method in order to reduce plasma damage.

Next, a resist mask319is formed over the conductive film302A by a lithography process or the like, and an unnecessary portion of the conductive film302A is removed. After that, the resist mask319is removed. In this manner, the conductive layer302acan be formed (FIG. 4B).

A method for processing a film is described. In the case of finely processing a film, a variety of fine processing techniques can be used. For example, a method may be used in which a resist mask formed by a lithography process or the like is subjected to slimming treatment. Alternatively, a dummy pattern is formed by a lithography process or the like, the dummy pattern is provided with a sidewall and then removed, and a film is etched using the remaining sidewall as a resist mask. To achieve a high aspect ratio, anisotropic dry etching is preferably used for etching of a film. Alternatively, a hard mask formed of an inorganic film or a metal film may be used.

As light used to form the resist mask, for example, light with an i-line (with a wavelength of 365 nm), light with a g-line (with a wavelength of 436 nm), light with an h-line (with a wavelength of 405 nm), or light in which the i-line, the g-line, and the h-line are mixed can be used. Alternatively, ultraviolet light, KrF laser light, ArF laser light, or the like can be used. Exposure may also be performed by a liquid immersion exposure technique. As light for the exposure, extreme ultra-violet light (EUV) or X-rays may be used. Instead of the light for the exposure, an electron beam can be used. It is preferable to use extreme ultra-violet light (EUV), X-rays, or an electron beam because extremely fine processing can be performed. In the case of performing exposure by scanning of a beam, such as an electron beam, a photomask is not needed.

Before a resist film that is processed into the resist mask is formed, an organic resin film having a function of improving adhesion between a film and the resist film may be formed. The organic resin film can be formed by, for example, a spin coating method to planarize a surface by covering a step thereunder and thus can reduce variation in thickness of the resist mask over the organic resin film. In the case of fine processing, in particular, a material serving as an anti-reflection film against light for the exposure is preferably used for the organic resin film. Examples of such an organic resin film serving as an anti-reflection film include a bottom anti-reflection coating (BARC) film. The organic resin film may be removed at the same time as the removal of the resist mask or after the removal of the resist mask.

Next, a conductive film302B and a barrier film303A are formed over the conductive layer302a. The conductive film302B can be formed in a manner similar to that of the conductive film302A. As the barrier film303A, an insulating film, such as a silicon oxide film or a gallium oxide film, or a semiconductor film, such as an oxide semiconductor film, can be used (FIG. 4C).

The barrier film303A can be formed by, for example, a sputtering method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), an MBE method, an ALD method, a PLD method, or the like. In particular, it is preferable that the barrier film303A be formed by a CVD method, more preferably, a plasma CVD method because coverage can be improved. It is preferable to use a thermal CVD method, an MOCVD method, or an ALD method in order to reduce plasma damage.

After that, a resist mask320is formed by a method similar to that described above, and unnecessary portions of the barrier film303A and the conductive film302B are removed by etching. Then, the resist mask320is removed, whereby the barrier layer303and the conductive layer302bare formed (FIG. 4D). When the conductive layer302bis formed, the first electrode302serving as one electrode of the capacitor300is completed.

The barrier film303A and the conductive film302B may be etched separately. In that case, the barrier layer303is first formed using the resist mask320, and then the barrier layer303is used as a hard mask to etch the conductive film302B.

Alternatively, the first electrode302including a protruding portion may be formed by processing one conductive film in such a manner that a barrier film is formed over a conductive film that is formed to be sufficiently thick. A technique, such as half etching, can be used for the processing. For example, as illustrated inFIGS. 5A and 5B, a resist mask330is formed over the barrier film303A and a conductive film302C that is formed to be sufficiently thick, and processing is performed to form a barrier film303B and a conductive film302c. After that, as illustrated inFIGS. 5C and 5D, the resist mask320is formed, and part of the barrier film303B and part of the conductive film302care removed. The conductive film302cmay be processed by timer etching in which the processing time corresponding to a desired etching amount is calculated from the etching rate of the conductive film302C and etching is stopped during the process using a timer. In this manner, the first electrode302can include a protruding portion as illustrated inFIG. 5D.

When an exposure method using an exposure mask including a semi-transmission portion, which is referred to as a half-tone exposure method, is used, the first electrode302can be formed using one mask. Alternatively, a photo mask or a reticle provided with an auxiliary pattern having a function of reducing light intensity, which is formed of a diffraction grating pattern, may be used in a lithography process for forming the first electrode302.

Next, the insulator304is formed over the first electrode302and the barrier layer303using a resist mask in a manner similar to that described above. The insulator304can be formed in a manner similar to that of the insulating film301(FIG. 4E).

A conductive film305A is formed over the insulator304(FIG. 6A). The conductive film305A can be formed in a manner similar to that of the conductive film302A. After that, a resist mask325is formed by a method similar to that described above, and an unnecessary portion of the conductive film305A is removed by etching, whereby the second electrode305is formed. At this time, not only the conductive film305A but also the surface of the insulator304is etched. Thus, the thickness of a region of the insulator304which does not overlaps with the second electrode305is smaller than that of a region of the insulator304which overlaps with the second electrode305. Furthermore, the surface of the insulator304is damaged by being exposed to plasma in the case of dry etching or to an etchant or the like in the case of wet etching. Therefore, without the barrier layer303, leakage current is likely to be generated in a region under the peripheral portion of the second electrode305. With the barrier layer303, the first electrode302and the second electrode305can be appropriately distanced from each other, leading to the capacitor300that is highly reliable, highly integrated, and miniaturized (FIG. 6B).

Then, an insulating film306that covers the capacitor300is formed. The insulating film306can be formed using a material and a method similar to those of the insulating film301and the like (FIG. 6C).

In addition, a wiring308may be formed so as to electrically connect the capacitor300to other semiconductor elements (FIG. 6D). The wiring308can be formed using a conductive material, such as a metal material, an alloy material, or a metal oxide material. In particular, the wiring308is preferably formed using a low-resistance conductive material, such as aluminum or copper. The use of the material as described above can reduce the wiring resistance.

Through the above steps, the capacitor of one embodiment of the present invention can be manufactured. The capacitor illustrated inFIGS. 1A and 1Bcan also be manufactured in a manner similar to that described above.

In this embodiment, one embodiment of the present invention is described. Other embodiments of the present invention are described in Embodiments 2 to 9. Note that one embodiment of the present invention is not limited to the above examples. In other words, various embodiments of the invention are described in this embodiment and other embodiments, and one embodiment of the present invention is not limited to a particular embodiment. For example, although an example in which the barrier layer is provided over the first electrode of the capacitor is described as one embodiment of the present invention, one embodiment of the present invention is not limited thereto. Depending on the case or circumstances, any of various layers may be provided over the first electrode of the capacitor in one embodiment of the present invention. Depending on the case or circumstances, a barrier layer is not necessarily provided over the first electrode of the capacitor in one embodiment of the present invention.

FIGS. 7A and 7Billustrate an example of a semiconductor device (memory device) in which the capacitor of one embodiment of the present invention is used. Note thatFIG. 7Bis a circuit diagram of the structure illustrated inFIG. 7A.

The semiconductor device illustrated inFIGS. 7A and 7Bincludes a first transistor100, a second transistor200, and a capacitor300. The capacitor described in Embodiment 1 can be used as the capacitor300.

The second transistor200is a transistor in which a channel is formed in a semiconductor layer including an oxide semiconductor. Since the off-state current of the second transistor200is small, by using the second transistor200in the semiconductor device (memory device), stored data can be held for a long time. In other words, power consumption can be sufficiently reduced because a semiconductor device (memory device) in which the refresh operation is unnecessary or the frequency of refresh operations is extremely low can be provided.

InFIG. 7B, a wiring3001is electrically connected to a source electrode of the first transistor100. A wiring3002is electrically connected to a drain electrode of the first transistor100. A wiring3003is electrically connected to one of a source electrode and a drain electrode of the second transistor200. A wiring3004is electrically connected to a gate electrode of the second transistor200. A gate electrode of the first transistor100and the other of the source electrode and the drain electrode of the second transistor200are electrically connected to one electrode of the capacitor300. A wiring3005is electrically connected to the other electrode of the capacitor300.

When semiconductor devices each having the structure illustrated inFIG. 7Aare arranged in a matrix, a memory device (memory cell array) can be manufactured.

The semiconductor device of one embodiment of the present invention includes the capacitor300in which the first electrode includes a protruding portion, which leads to a smaller area and higher integration of the semiconductor device. In the capacitor300, at least the distance between the electrodes in a region where the top surface of the protruding portion of the first electrode overlaps with an edge of the second electrode is longer than that at the side surface of the protruding portion of the first electrode; with such a structure, short-circuit between the electrodes can be prevented.

The semiconductor device illustrated inFIG. 7Aincludes the first transistor100, the second transistor200, and the capacitor300. The second transistor200is provided over the first transistor100. The capacitor300is provided between the first transistor100and the second transistor200.

The first transistor100is provided on a semiconductor substrate101and includes a semiconductor film102that is part of the semiconductor substrate101, a gate insulating film104, a gate electrode105, and low-resistance layers103aand103bserving as source and drain regions.

The first transistor100may be either a p-channel transistor or an n-channel transistor, and an appropriate transistor may be used depending on the circuit configuration or the driving method.

It is preferable that a region of the semiconductor film102where a channel is formed, a region in the vicinity thereof, the low-resistance layers103aand103bserving as source and drain regions, and the like include a semiconductor, such as a silicon-based semiconductor, more preferably, single crystal silicon. Alternatively, a material including germanium (Ge), silicon germanium (SiGe), gallium arsenide (GaAs), gallium aluminum arsenide (GaAlAs), or the like may be used. Silicon whose effective mass is controlled by applying stress to the crystal lattice and thereby changing the lattice spacing may also be used. Alternatively, the first transistor100may be formed as a high-electron-mobility transistor (HEMT) with the use of, for example, GaAs and GaAlAs.

The low-resistance layers103aand103bcontain an element that imparts n-type conductivity, such as arsenic or phosphorus, or an element that imparts p-type conductivity, such as boron, in addition to a semiconductor material used for the semiconductor film102.

The gate electrode105can be formed using a semiconductor material, such as silicon, containing the element that imparts n-type conductivity, such as arsenic or phosphorus, or the element that imparts p-type conductivity, such as boron, or a conductive material, such as a metal material, an alloy material, or a metal oxide material. To adjust the threshold voltage of the transistor, the work function is preferably adjusted by utilizing the gate electrode. Specifically, it is preferable to use titanium nitride, tantalum nitride, or the like for the gate electrode. Furthermore, to ensure conductivity and embeddability of the gate electrode, it is preferable that the gate electrode be a stack of metal materials, such as tungsten and aluminum. In particular, tungsten is preferable in terms of heat resistance.

The first transistor100may be a transistor as illustrated inFIG. 8.FIG. 8illustrates a cross section of the first transistor100in the channel length direction on the left side of the dashed-dotted line and a cross section of the first transistor100in the channel width direction on the right side of the dashed-dotted line. In the first transistor100illustrated inFIG. 8, the semiconductor film102(part of the semiconductor substrate101) in which a channel is formed includes a protruding portion. In addition, gate electrodes105aand105bare provided so as to cover the side surface and the top surface of the semiconductor film102with the gate insulating film104provided therebetween. Note that the gate electrode105amay be formed using a material with which the work function can be adjusted. The first transistor100which utilizes the protruding portion of the semiconductor substrate is also referred to as a fin-type transistor. An insulating film serving as a mask for forming the protruding portion may be provided in contact with the top surface of the protruding portion. Although the case where the protruding portion is formed by processing part of the semiconductor substrate is described here, a semiconductor film including a protruding portion may be formed by processing an SOI substrate.

An insulating film121, an insulating film122, and an insulating film301are stacked in this order so as to cover the first transistor100.

The insulating film121serves as a planarization film for eliminating a level difference generated by the first transistor100or the like underlying the insulating film121. The top surface of the insulating film121may be planarized by planarization treatment using a chemical mechanical polishing (CMP) method or the like to increase the level of planarity.

A wiring110that is electrically connected to the capacitor300or the second transistor200and the like are embedded in the insulating film121, the insulating film122, and the insulating film301. Note that in this specification and the like, an electrode and a wiring electrically connected to the electrode may be a single component. In other words, there are cases where part of a wiring serves as an electrode and where part of an electrode serves as a wiring.

Wirings (a wiring308and the like) can be formed using a conductive material, such as a metal material, an alloy material, or a metal oxide material. It is preferable to use a high-melting-point material which has both heat resistance and conductivity, such as tungsten or molybdenum, and it is particularly preferable to use tungsten. Also, it is particularly preferable to use a low-resistance conductive material, such as aluminum or copper. The use of the above-described materials can reduce the wiring resistance.

A first electrode302of the capacitor300is provided over the insulating film301and the wiring308. The first electrode302is electrically connected to the wiring308.

A barrier layer303and an insulator304are provided over the first electrode302of the capacitor300, and a second electrode305of the capacitor300is provided over the insulator304.

It is preferable that the capacitor300be embedded in an insulating film306and that the top surface of the insulating film306be planarized.

An insulating film is formed over the insulating film306. Although two layers, an insulating film201and an insulating film202, are formed in this embodiment, one layer or a stack of three or more layers may be formed.

The insulating film202is preferably formed using an oxide material from which part of oxygen is released by heating.

As the oxide material from which oxygen is released by heating, oxide containing oxygen in excess of the stoichiometric composition is preferably used. Part of oxygen is released by heating from an oxide film containing oxygen in excess of the stoichiometric composition. The oxide film containing oxygen in excess of the stoichiometric composition is an oxide film in which the amount of released oxygen converted into oxygen atoms is greater than or equal to 1.0×1018atoms/cm3, preferably greater than or equal to 3.0×1020atoms/cm3in thermal desorption spectroscopy (TDS) analysis. Note that the temperature of the film surface in the TDS analysis is preferably higher than or equal to 100° C. and lower than or equal to 700° C., or higher than or equal to 100° C. and lower than or equal to 500° C.

For example, as such a material, a material containing silicon oxide or silicon oxynitride is preferably used. Alternatively, a metal oxide can be used. Note that in this specification, “silicon oxynitride” refers to a material that contains oxygen at a higher proportion than nitrogen, and “silicon nitride oxide” refers to a material that contains nitrogen at a higher proportion than oxygen.

The second transistor200is provided over the insulating film202.

One of electrodes204aand204bserves as a source electrode, and the other serves as a drain electrode.

The electrodes204aand204bare formed to have a single-layer structure or a stacked-layer structure using any of metals, such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten, or an alloy containing any of these metals as its main component. For example, a single-layer structure of an aluminum film containing silicon, a two-layer structure in which an aluminum film is stacked over a titanium film, a two-layer structure in which 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 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, or the like can be used. Note that a transparent conductive material containing indium oxide, tin oxide, or zinc oxide may also be used.

A gate insulating film205can be formed to have a single-layer structure or a stacked-layer structure using, for example, an insulating film containing a so-called high-k material, such as silicon oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3(BST). Alternatively, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide may be added to the above insulating film. Alternatively, the insulating film may be subjected to nitriding treatment. A layer of silicon oxide, silicon oxynitride, or silicon nitride may also be stacked over the insulating film.

As the gate insulating film205, like the insulating film202, an oxide insulating film containing oxygen in excess of the stoichiometric composition is preferably used.

When a specific material is used for the gate insulating film, electrons are trapped in the gate insulating film under specific conditions, and the threshold voltage can be thus increased. For example, a material having a lot of electron trap states, such as hafnium oxide, aluminum oxide, or tantalum oxide, is used as part of the gate insulating film, like a stacked-layer film of silicon oxide and hafnium oxide, and the state where the potential of the gate electrode is higher than that of the source electrode or the drain electrode is kept for ten milliseconds or more, typically one minute or more at a higher temperature (a temperature of higher than the operating temperature or the storage temperature of the semiconductor device, or a temperature of higher than or equal to 125° C. and lower than or equal to 450° C., typically higher than or equal to 150° C. and lower than or equal to 300° C.). Thus, electrons are moved from the semiconductor film to the gate electrode, and some of the electrons are trapped by the electron trap states.

In such a transistor in which a necessary amount of electrons is trapped by the electron trap states, the threshold voltage is shifted in the positive direction. By controlling the voltage of the gate electrode, the amount of trapped electrons can be controlled, and thus, the threshold voltage can be controlled. Treatment for trapping the electrons may be performed in the manufacturing process of the transistor.

For example, the treatment is preferably performed at any step before factory shipment, such as after the formation of a wiring connected to the source electrode or the drain electrode of the transistor, after pretreatment (wafer processing), after a wafer-dicing step, after packaging, or the like. In either case, it is preferable that the semiconductor device be not exposed to temperatures of higher than or equal to 125° C. for one hour or more after the treatment for trapping electrons.

A gate electrode206including conductors206aand206bcan be formed using, for example, a metal selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, and tungsten, an alloy containing any of these metals as its component, an alloy containing any of these metals in combination, or the like. Alternatively, one or more metals selected from manganese and zirconium may be used. Further alternatively, a semiconductor typified by polycrystalline silicon doped with an impurity element, such as phosphorus, or a silicide, such as nickel silicide, may be used. For example, a two-layer structure in which a titanium film is stacked over an aluminum film, a two-layer structure in which a titanium film is stacked over a titanium nitride film, a two-layer structure in which a tungsten film is stacked over a titanium nitride film, a two-layer structure in which a tungsten film is stacked over a tantalum nitride film or a tungsten nitride film, a three-layer structure in which a titanium film, an aluminum film, and a titanium film are stacked in this order, or the like can be used. Alternatively, an alloy film containing aluminum and one or more metals selected from titanium, tantalum, tungsten, molybdenum, chromium, neodymium, and scandium, or a nitride film thereof may be used.

The gate electrode206can also be formed using a light-transmitting conductive material, such as indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, or indium tin oxide to which silicon oxide is added. It is also possible to have a stacked-layer structure formed using the above light-transmitting conductive material and the above metal.

Another structural example of a transistor that can be used as the second transistor200is described.FIG. 9Ais a schematic top view of a transistor described below as an example, andFIGS. 9B and 9Care schematic cross-sectional views taken along section lines A1-A2and B1-B2, respectively, inFIG. 9A. Note thatFIG. 9Bcorresponds to a cross section of the transistor in the channel length direction, andFIG. 9Ccorresponds to a cross section of the transistor in the channel width direction.

As illustrated inFIG. 9C, the gate electrode206is provided so as to face the top surface and the side surface of an oxide semiconductor layer203bin a cross section of the transistor in the channel width direction. Thus, a channel is formed not only in the vicinity of the top surface but also in the vicinity of the side surface of the oxide semiconductor layer203b, and the effective channel width is increased, which results in increased current in an on state (i.e., on-state current) of the transistor. In particular, in the case where the width of the oxide semiconductor layer203bis extremely small (for example, less than or equal to 50 nm, preferably less than or equal to 30 nm, more preferably less than or equal to 20 nm), the proportion of a region where a channel is formed is increased inside the oxide semiconductor layer203b. Thus, as the miniaturization advances, contribution of this structure to on-state current increases.

The width of the gate electrode206may be made small as illustrated inFIGS. 10A to 10C. In that case, an impurity, such as argon, hydrogen, phosphorus, or boron, can be introduced into the oxide semiconductor layer203band the like using the electrodes204aand204b, the gate electrode206, and the like as a mask, for example. As a result, low-resistance regions209aand209bcan be provided in the oxide semiconductor layer203band the like. Note that the low-resistance regions209aand209bare not necessarily provided. The width of the gate electrode206can be made small not only in the structure illustrated inFIGS. 9A to 9Cbut also in other structures.

A transistor illustrated inFIGS. 11A and 11Bdiffers from the transistor illustrated inFIGS. 9A to 9Cmainly in that an oxide semiconductor layer203cis provided in contact with bottom surfaces of the electrodes204aand204b.

Such a structure enables films used for an oxide semiconductor layer203a, the oxide semiconductor layer203b, and the oxide semiconductor layer203cto be formed successively without contact with the air, which can reduce defects at each interface.

Although the oxide semiconductor layers203aand203care provided in contact with the oxide semiconductor layer203bin the above-described structure, one of the oxide semiconductor layers203aand203cor neither of them may be provided.

Note that the width of the gate electrode206can be made small in the structure illustrated inFIGS. 11A and 11Bas in the structure illustrated inFIGS. 9A to 9C. An example in that case is illustrated inFIGS. 12A and 12B. Note that the width of the gate electrode206can be made small not only in the structures illustrated inFIGS. 9A to 9CandFIGS. 11A and 11Bbut also in other structures.

Note that the channel length refers to, for example, the distance between a source (a source region or a source electrode) and a drain (a drain region or a drain electrode) in a region where a semiconductor (or a portion where a current flows in a semiconductor when a transistor is on) and a gate electrode overlap with each other or a region where a channel is formed in a top view of the transistor. In one transistor, channel lengths in all regions are not necessarily the same. In other words, the channel length of one transistor is not limited to one value in some cases. Therefore, in this specification, the channel length is any one of values, the maximum value, the minimum value, or the average value, in a region where a channel is formed.

The channel width refers to, for example, the length of a portion where a source and a drain face each other in a region where a semiconductor (or a portion where a current flows in a semiconductor when a transistor is on) and a gate electrode overlap with each other or a region where a channel is formed. In one transistor, channel widths in all regions are not necessarily the same. In other words, the channel width of one transistor is not limited to one value in some cases. Therefore, in this specification, the channel width is any one of values, the maximum value, the minimum value, or the average value, in a region where a channel is formed.

Note that depending on the structure of a transistor, the channel width in a region where a channel is formed actually (hereinafter referred to as an effective channel width) is different from the channel width shown in a top view of the transistor (hereinafter referred to as an apparent channel width) in some cases. For example, in a transistor having a three-dimensional structure, the effective channel width is larger than the apparent channel width shown in a top view of the transistor, and its influence cannot be ignored in some cases. For example, in a miniaturized transistor having a three-dimensional structure, the proportion of a channel region formed at the side surface of a semiconductor is high in some cases. In that case, the effective channel width in a region where a channel is actually formed is larger than the apparent channel width shown in the top view.

In a transistor having a three-dimensional structure, the effective channel width is difficult to measure in some cases. For example, estimation of the effective channel width from a design value requires an assumption that the shape of a semiconductor is known. Therefore, in the case where the shape of a semiconductor is not accurately known, it is difficult to measure the effective channel width accurately.

Thus, in this specification, the apparent channel width that is the length of a portion where a source and a drain face each other in a region where a semiconductor and a gate electrode overlap with each other in a top view of a transistor is referred to as a surrounded channel width (SCW) in some cases. Furthermore, in this specification, in the case where the term “channel width” is simply used, it may denote the surrounded channel width or the apparent channel width. Alternatively, in this specification, in the case where the term “channel width” is simply used, it may denote the effective channel width. Note that the values of the channel length, the channel width, the effective channel width, the apparent channel width, the surrounded channel width, and the like can be determined by obtaining and analyzing a cross-sectional TEM image and the like.

Note that in the case where the field-effect mobility, a current value per channel width, and the like of a transistor are obtained by calculation, the surrounded channel width may be used for the calculation. In that case, the values may be different from those calculated using the effective channel width.

The above is the description of the second transistor200.

An insulating film207and an insulating film208covering the second transistor200may serve as a barrier film or a planarization film which covers an uneven surface of an underlying layer.

The above is the description of the structural example.

[Example of Manufacturing Method]

An example of a method for manufacturing the semiconductor device described in the above structural example will be described below with reference toFIGS. 13A to 13C,FIGS. 14A and 14B, andFIG. 15.

First, the semiconductor substrate101is prepared. As the semiconductor substrate101, for example, a single crystal silicon substrate (including a p-type semiconductor substrate or an n-type semiconductor substrate), a compound semiconductor substrate containing silicon carbide or gallium nitride, or the like can be used. An SOI substrate may also be used as the semiconductor substrate101. The case where single crystal silicon is used for the semiconductor substrate101is described below.

Next, an element isolation layer is formed in the semiconductor substrate101. The element isolation layer may be formed by a local oxidation of silicon (LOCOS) method, a shallow trench isolation (STI) method, or the like.

In the case where a p-channel transistor and an n-channel transistor are formed on the same substrate, an n-well or a p-well may be formed in part of the semiconductor substrate101. For example, a p-well may be formed by adding an impurity element that imparts p-type conductivity, such as boron, to the n-type semiconductor substrate101, and an n-channel transistor and a p-channel transistor may be formed on the same substrate.

Next, an insulating film to be the gate insulating film104is formed over the semiconductor substrate101. For example, after surface nitriding treatment, oxidizing treatment may be performed to oxidize the interface between silicon and silicon nitride, whereby a silicon oxynitride film may be formed. For example, a silicon oxynitride film can be obtained by performing oxygen radical oxidation after a thermal silicon nitride film is formed on the surface at 700° C. in an NH3atmosphere.

The insulating film may also be formed by a sputtering method, a chemical vapor deposition (CVD) method (including a thermal CVD method, a metal organic CVD (MOCVD) method, a plasma enhanced CVD (PECVD) method, and the like), a molecular beam epitaxy (MBE) method, an atomic layer deposition (ALD) method, a pulsed laser deposition (PLD) method, or the like.

Next, a conductive film to be the gate electrode105is formed. It is preferable that the conductive film be formed using a metal selected from tantalum, tungsten, titanium, molybdenum, chromium, niobium, and the like, or an alloy material or a compound material containing any of these metals as its main component. Alternatively, polycrystalline silicon to which an impurity, such as phosphorus, is added can be used. Further alternatively, a stacked-layer structure including a metal nitride film and a film of any of the above metals may be used. As a metal nitride, tungsten nitride, molybdenum nitride, or titanium nitride can be used. When the metal nitride film is provided, adhesiveness of the metal film can be increased; thus, separation can be prevented. A metal film which controls the work function of the gate electrode105may be used.

The conductive film can be formed by a sputtering method, an evaporation method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), or the like. It is preferable to use a thermal CVD method, an MOCVD method, or an ALD method in order to reduce plasma damage.

Next, a resist mask is formed over the conductive film by a lithography process or the like, and an unnecessary portion of the conductive film is removed. After that, the resist mask is removed. In this manner, the gate electrode105can be formed.

A method for processing a film is described. In the case of finely processing a film, a variety of fine processing techniques can be used. For example, a method may be used in which a resist mask formed by a lithography process or the like is subjected to slimming treatment. Alternatively, a dummy pattern is formed by a lithography process or the like, the dummy pattern is provided with a sidewall and then removed, and a film is etched using the remaining sidewall as a resist mask. To achieve a high aspect ratio, anisotropic dry etching is preferably used for etching of a film. Alternatively, a hard mask formed of an inorganic film or a metal film may be used.

As light used to form the resist mask, for example, light with an i-line (with a wavelength of 365 nm), light with a g-line (with a wavelength of 436 nm), light with an h-line (with a wavelength of 405 nm), or light in which the i-line, the g-line, and the h-line are mixed can be used. Alternatively, ultraviolet light, KrF laser light, ArF laser light, or the like can be used. Exposure may also be performed by a liquid immersion exposure technique. As the light for the exposure, extreme ultra-violet light (EUV) or X-rays may be used. Instead of the light for the exposure, an electron beam can be used. It is preferable to use extreme ultra-violet light (EUV), X-rays, or an electron beam because extremely fine processing can be performed. Note that in the case of performing exposure by scanning of a beam, such as an electron beam, a photomask is not needed.

Before a resist film that is processed into the resist mask is formed, an organic resin film having a function of improving adhesion between a film and the resist film may be formed. The organic resin film can be formed by, for example, a spin coating method to planarize a surface by covering a step thereunder and thus can reduce variation in thickness of the resist mask over the organic resin film. In the case of fine processing, in particular, a material serving as an anti-reflection film against light for the exposure is preferably used for the organic resin film. Examples of such an organic resin film serving as an anti-reflection film include a bottom anti-reflection coating (BARC) film. The organic resin film may be removed at the same time as the removal of the resist mask or after the removal of the resist mask.

After the gate electrode105is formed, a sidewall covering the side surface of the gate electrode105may be formed. The sidewall can be formed in such a manner that an insulating film thicker than the gate electrode105is formed and subjected to anisotropic etching so that only a portion of the insulating film on the side surface of the gate electrode105remains.

The insulating film to be the gate insulating film104is etched at the same time as the formation of the sidewall, whereby the gate insulating film104is formed under the gate electrode105and the sidewall. Alternatively, after the gate electrode105is formed, the insulating film may be etched using the gate electrode105or a resist mask for forming the gate electrode105as an etching mask, thereby forming the gate insulating film104. Alternatively, the insulating film can be used as the gate insulating film104without being processed by etching.

Next, an element that imparts n-type conductivity, such as phosphorus, or an element that imparts p-type conductivity, such as boron, is added to a region of the semiconductor substrate101where the gate electrode105(and the sidewall) is not provided.FIG. 13Ais a schematic cross-sectional view at this stage.

Next, the insulating film121is formed, and then, first heat treatment is performed to activate the aforementioned element that imparts conductivity.

The insulating film121can be formed to have a single-layer structure or a stacked-layer structure using, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminum nitride, or the like. The insulating film121is preferably formed using silicon nitride containing oxygen and hydrogen (SiNOH) because the amount of hydrogen released by heating can be increased. Alternatively, the insulating film121can also be formed using silicon oxide with high step coverage that is formed by reacting tetraethyl orthosilicate (TEOS), silane, or the like with oxygen, nitrous oxide, or the like.

The insulating film121can be formed by, for example, a sputtering method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), an MBE method, an ALD method, a PLD method, or the like. In particular, it is preferable that the insulating film be formed by a CVD method, more preferably, a plasma CVD method because coverage can be improved. It is preferable to use a thermal CVD method, an MOCVD method, or an ALD method in order to reduce plasma damage.

The first heat treatment can be performed, for example, at a temperature of higher than or equal to 400° C. and lower than the strain point of the substrate in an inert gas atmosphere, such as a rare gas atmosphere or a nitrogen gas atmosphere, or in a reduced-pressure atmosphere.

At this stage, the first transistor100is completed.

Next, the top surface of the insulating film121is planarized by a CMP method or the like.

Next, openings that reach the low-resistance layers103aand103b, the gate electrode105, and the like are formed in the insulating film121. After that, a conductive film is formed so as to fill the openings, and the conductive film is subjected to planarization treatment to expose the top surface of the insulating film121, whereby a wiring111a, a wiring111b, a wiring110, and the like are formed. The conductive film can be formed by, for example, a sputtering method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), an MBE method, an ALD method, a PLD method, or the like.

A conductive film is then formed over the insulating film121. Then, a resist mask is formed by a method similar to that described above, and an unnecessary portion of the conductive film is removed by etching. After that, the resist mask is removed; thus, wirings are formed. Then, the insulating film122is formed and planarized by a CMP method or the like so that the top surfaces of the wirings are exposed. In this manner, embedded wirings are formed. Alternatively, the embedded wirings may be formed by a damascene method. Note that the insulating film122can be formed using a material and a method similar to those of the insulating film121.

Next, the insulating film301is formed, and a contact hole that reaches the wiring connected to the wiring110is formed in the insulating film301. Then, the wiring308is formed using a material and a method similar to those of the wiring110.FIG. 13Bis a schematic cross-sectional view at this stage.

Then, the capacitor300is formed so as to be connected to the wiring308by the manufacturing method described in Embodiment 1.FIG. 13Cis a schematic cross-sectional view at the stage after the formation of the capacitor300.

Then, an insulating film to be the insulating film306that covers the capacitor300is formed. The insulating film to be the insulating film306can be formed using a material and a method similar to those of the insulating film121or the like.

After the insulating film to be the insulating film306is formed, the insulating film may be subjected to planarization treatment using a CMP method or the like to improve the level of planarity of the top surface, thereby forming the insulating film306.

Then, an insulating film to be the insulating film201and an insulating film to be the insulating film202are formed. The insulating film to be the insulating film201and the insulating film to be the insulating film202can each be formed by, for example, a sputtering method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), an MBE method, an ALD method, a PLD method, or the like. In particular, it is preferable that the insulating films be formed by a CVD method, more preferably, a plasma CVD method because coverage can be improved. It is preferable to use a thermal CVD method, an MOCVD method, or an ALD method in order to reduce plasma damage.

To make the insulating film to be the insulating film202contain excess oxygen, the insulating film to be the insulating film202may be formed in an oxygen atmosphere, for example. Alternatively, a region containing excess oxygen may be formed by introducing oxygen into the insulating film to be the insulating film202that has been formed. These two methods may also be combined.

For example, oxygen (including at least one of an oxygen radical, an oxygen atom, and an oxygen ion) is introduced into the insulating film to be the insulating film202that has been formed, so that a region containing excess oxygen is formed. Oxygen can be introduced by an ion implantation method, an ion doping method, a plasma immersion ion implantation method, plasma treatment, or the like.

A gas containing oxygen can be used for oxygen introducing treatment. As the gas containing oxygen, oxygen, dinitrogen monoxide, nitrogen dioxide, carbon dioxide, carbon monoxide, or the like can be used. Furthermore, a rare gas may be contained in the gas containing oxygen for the oxygen introducing treatment. For example, a mixed gas of carbon dioxide, hydrogen, and argon can be used.

After the insulating film to be the insulating film202is formed, the insulating film may be subjected to planarization treatment using a CMP method or the like to improve the level of planarity of the top surface, thereby forming the insulating film202.

Next, an oxide semiconductor film to be the oxide semiconductor layer203aand an oxide semiconductor film to be the oxide semiconductor layer203bare formed in this order. The oxide semiconductor films are preferably formed successively without contact with the air.

After the oxide semiconductor film to be the oxide semiconductor layer203bis formed, heat treatment is preferably performed. The heat treatment may be performed at a temperature of 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., in an inert gas atmosphere, an atmosphere containing an oxidizing gas at 10 ppm or more, or a reduced pressure state. Alternatively, the heat treatment may be performed in such a manner that heat treatment is performed in an inert gas atmosphere, and then another heat treatment is performed in an atmosphere containing an oxidization gas at 10 ppm or more, in order to compensate desorbed oxygen. The heat treatment may be performed directly after the formation of the oxide semiconductor film to be the oxide semiconductor layer203bor may be performed after the oxide semiconductor film to be the oxide semiconductor layer203bis processed into the island-shaped oxide semiconductor layer203b. Through the heat treatment, oxygen can be supplied to the oxide semiconductor layer from the insulating film202; thus, oxygen vacancies in the oxide semiconductor layer can be reduced.

Next, over the oxide semiconductor film to be the oxide semiconductor layer203b, a conductive film to be a hard mask is formed, and a resist mask is formed by a method similar to that described above; then, an unnecessary portion of the conductive film is removed by etching. After that, unnecessary portions of the oxide semiconductor films are removed by etching using the conductive film as a mask. Then, the resist mask is removed. In this manner, a stacked-layer structure including the island-shaped oxide semiconductor layers203aand203bcan be formed. Note that the conductive film serving as a hard mask may be used as part of the electrodes204aand204bthat are formed later.

Then, a resist mask is formed over the insulating film202and the island-shaped oxide semiconductor layers203aand203b, and a contact hole310that penetrates the insulating film202, the insulating film201, the insulating film306, the insulator304, and the barrier layer303is formed (seeFIG. 14A).

Then, a conductive film is formed. The conductive film can be formed by, for example, a sputtering method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), an MBE method, an ALD method, a PLD method, or the like. In particular, it is preferable that the conductive film be formed by a CVD method, more preferably, a plasma CVD method because coverage can be improved. It is preferable to use a thermal CVD method, an MOCVD method, or an ALD method in order to reduce plasma damage.

Next, a resist mask is formed over the conductive film by a method similar to that described above, and an unnecessary portion of the conductive film is removed by etching. After that, the resist mask is removed. In this manner, the electrodes204aand204band a wiring307that connects the electrode204ato the first electrode302of the capacitor300through the contact hole310can be formed at the same time.

Then, an oxide semiconductor film to be the oxide semiconductor layer203cand an insulating film are formed in this order. A resist mask is formed over the insulating film by a method similar to that described above, and unnecessary portions of the insulating film and the oxide semiconductor film are removed by etching. Then, the resist mask is removed, so that the oxide semiconductor layer203cand the gate insulating film205are formed.

Next, conductive films are formed, and the gate electrode206including the conductors206aand206bis formed.

At this stage, the second transistor200is completed.

Then, the insulating film207is formed, and the insulating film208is formed as necessary. The insulating film207and the insulating film208can each be formed by, for example, a sputtering method, a CVD method (including a thermal CVD method, an MOCVD method, a PECVD method, and the like), an MBE method, an ALD method, or a PLD method. In particular, it is preferable that the insulating films be formed by a CVD method, more preferably, a plasma CVD method because coverage can be improved. It is preferable to use a thermal CVD method, an MOCVD method, or an ALD method in order to reduce plasma damage (seeFIG. 14B).

Through the above steps, the semiconductor device of one embodiment of the present invention can be manufactured.

FIG. 15illustrates a modification example of this embodiment, in which the capacitor300is provided over the second transistor200. Specifically, after the second transistor200is formed over the first transistor100, the capacitor300is formed. The first transistor100is connected to the second transistor200through a wiring250. In addition, a contact hole is formed in an interlayer insulating film so as to reach a wiring that is formed in the same layer as the electrode204bof the second transistor200. A wiring350is formed in the contact hole, so that the capacitor300, the first transistor100, and the second transistor200can be electrically connected to each other.

Furthermore, as illustrated inFIGS. 16A and 16B, one of the source electrode and the drain electrode of the second transistor200and the first electrode of the capacitor300may be formed using the same conductive layer. Therefore, the electrode204bin the drawings serves as one of the source electrode and the drain electrode of the second transistor200and the first electrode of the capacitor300.

Specific description ofFIG. 16Ais given below. A conductive film to be the electrode204bis formed to be sufficiently thick. A resist mask is formed by a method similar to that described above, and an unnecessary portion of the conductive film is removed. Next, the resist mask is removed, and an oxide semiconductor film to be the oxide semiconductor layer203cand the barrier layer303is formed. A resist mask is formed by a method similar to that described above, and an unnecessary portion of the oxide semiconductor film is removed. The resist mask is removed, so that the oxide semiconductor layer203cand the barrier layer303are formed.

Then, the oxide semiconductor layer203cand the barrier layer303are used as a mask, and the conductive film to be the electrode204bis subjected to half etching in such a manner that the insulating film202is not exposed, whereby the electrode204bserving as one of the source electrode and the drain electrode of the second transistor200and the first electrode of the capacitor300can be formed.

Then, the insulator304(the gate insulating film205) is formed. Conductive films are formed over the insulator304. Then, a resist mask is formed in a manner similar to that described above, and unnecessary portions of the conductive films are removed, whereby the second transistor200and the capacitor300can be formed at the same time.

Specific description ofFIG. 16Bis given below. The electrode204bserving as one of the source electrode and the drain electrode of the second transistor200and part of the first electrode of the capacitor300is formed. After the conductive layer302bthat is a protruding portion of the first electrode and the barrier layer303of the capacitor300are formed, an oxide semiconductor film to be the oxide semiconductor layer203cand an intermediate layer340, an insulating film to be the insulator304and the gate insulating film205, and conductive films to be the second electrode305including conductors305aand305band the gate electrode206including the conductors206aand206bare formed. A resist mask is formed in a manner similar to that described above, and unnecessary portions of the oxide semiconductor film, the insulating film, and the conductive films are removed, whereby the second transistor200and the capacitor300can be formed at the same time.

With the structure illustrated inFIG. 16A or 16B, the semiconductor device can be suitable for miniaturization and can have higher density with a reduction or without an increase in the number of steps and masks.

In this embodiment, an oxide semiconductor that can be favorably used for a semiconductor film of the semiconductor device of one embodiment of the present invention will be described.

The structure of an oxide semiconductor is described below.

From another perspective, an oxide semiconductor is classified into an amorphous oxide semiconductor and a crystalline oxide semiconductor. Examples of a crystalline oxide semiconductor include a single crystal oxide semiconductor, a CAAC-OS, a polycrystalline oxide semiconductor, and an nc-OS.

It is known that an amorphous structure is generally defined as being metastable and unfixed, and being isotropic and having no non-uniform structure. In other words, an amorphous structure has a flexible bond angle and a short-range order but does not have a long-range order.

This means that an inherently stable oxide semiconductor cannot be regarded as a completely amorphous oxide semiconductor. Moreover, an oxide semiconductor that is not isotropic (e.g., an oxide semiconductor that has a periodic structure in a microscopic region) cannot be regarded as a completely amorphous oxide semiconductor. Note that an a-like OS has a periodic structure in a microscopic region, but at the same time contains a void and has an unstable structure. For this reason, an a-like OS has physical properties similar to those of an amorphous oxide semiconductor.

The CAAC-OS is one of oxide semiconductors having a plurality of c-axis aligned crystal parts.

In a combined analysis image (also referred to as a high-resolution transmission electron microscope (TEM) image) of a bright-field image and a diffraction pattern of the CAAC-OS, which is obtained using a TEM, a plurality of crystal parts can be observed. However, in the high-resolution TEM image, a boundary between crystal parts, that is, a grain boundary is not clearly observed. Thus, in the CAAC-OS, a reduction in electron mobility due to the grain boundary is less likely to occur.

FIG. 17Bis an enlarged Cs-corrected high-resolution TEM image of a region (1) inFIG. 17A.FIG. 17Bshows that metal atoms are arranged in a layered manner in a crystal part. Each metal atom layer has a configuration reflecting unevenness of a surface over which the CAAC-OS is formed (hereinafter, the surface is referred to as a formation surface) or a top surface of the CAAC-OS, and is arranged parallel to the formation surface or the top surface of the CAAC-OS.

As shown inFIG. 17B, the CAAC-OS has a characteristic atomic arrangement. The characteristic atomic arrangement is denoted by an auxiliary line inFIG. 17C.FIGS. 17B and 17Cprove that the size of a crystal part is approximately 1 nm to 3 nm, and the size of a space caused by tilt of the crystal parts is approximately 0.8 nm. Therefore, the crystal part can also be referred to as a nanocrystal (nc). Furthermore, the CAAC-OS can also be referred to as an oxide semiconductor including c-axis aligned nanocrystals (CANC).

Here, according to the Cs-corrected high-resolution TEM images, the schematic arrangement of crystal parts5100of a CAAC-OS over a substrate5120is illustrated by such a structure in which bricks or blocks are stacked (seeFIG. 17D). The part in which the crystal parts are tilted as observed inFIG. 17Ccorresponds to a region5161shown inFIG. 17D.

FIG. 18Ashows a Cs-corrected high-resolution TEM image of a plane of the CAAC-OS observed in a direction substantially perpendicular to the sample surface.FIGS. 18B, 18C, and 18Dare enlarged Cs-corrected high-resolution TEM images of regions (1), (2), and (3) inFIG. 18A, respectively.FIGS. 18B, 18C, and 18Dindicate that metal atoms are arranged in a triangular, quadrangular, or hexagonal configuration in a crystal part. However, there is no regularity of arrangement of metal atoms between different crystal parts.

Next, a CAAC-OS analyzed by X-ray diffraction (XRD) is described. For example, when the structure of a CAAC-OS including an InGaZnO4crystal is analyzed by an out-of-plane method, a peak appears at a diffraction angle (2θ) of around 31° as shown inFIG. 19A. This peak is derived from the (009) plane of the InGaZnO4crystal, which indicates that crystals in the CAAC-OS have c-axis alignment, and that the c-axes are aligned in a direction substantially perpendicular to the formation surface or the top surface of the CAAC-OS.

Note that in structural analysis of the CAAC-OS by an out-of-plane method, another peak may appear when 2θ is around 36°, in addition to the peak at 2θ of around 31°. The peak of 2θ at around 36° indicates that a crystal having no c-axis alignment is included in part of the CAAC-OS. It is preferable that in the CAAC-OS analyzed by an out-of-plane method, a peak appear when 2θ is around 31° and that a peak not appear when 2θ is around 36°.

On the other hand, in structural analysis of the CAAC-OS by an in-plane method in which an X-ray is incident on a sample in a direction substantially perpendicular to the c-axis, a peak appears when 2θ is around 56°. This peak is derived from the (110) plane of the InGaZnO4crystal. In the case of the CAAC-OS, when analysis (ϕ scan) is performed with 2θ fixed at around 56° and with the sample rotated using a normal vector of the sample surface as an axis (ϕ axis), as shown inFIG. 19B, a peak is not clearly observed. In contrast, in the case of a single crystal oxide semiconductor of InGaZnO4, when ϕ scan is performed with 2θ fixed at around 56°, as shown inFIG. 19C, six peaks which are derived from crystal planes equivalent to the (110) plane are observed. Accordingly, the structural analysis using XRD shows that the directions of a-axes and b-axes are irregularly oriented in the CAAC-OS.

Next, a CAAC-OS analyzed by electron diffraction is described. For example, when an electron beam with a probe diameter of 300 nm is incident on a CAAC-OS including an InGaZnO4crystal in a direction parallel to the sample surface, a diffraction pattern (also referred to as a selected-area transmission electron diffraction pattern) shown inFIG. 20Acan be obtained. In this diffraction pattern, spots derived from the (009) plane of an InGaZnO4crystal are included. Thus, the electron diffraction also indicates that crystal parts included in the CAAC-OS have c-axis alignment and that the c-axes are aligned in a direction substantially perpendicular to the formation surface or the top surface of the CAAC-OS. Meanwhile,FIG. 20Bshows a diffraction pattern obtained in such a manner that an electron beam with a probe diameter of 300 nm is incident on the same sample in a direction perpendicular to the sample surface. As shown inFIG. 20B, a ring-like diffraction pattern is observed. Thus, the electron diffraction also indicates that the a-axes and b-axes of the crystal parts included in the CAAC-OS do not have regular alignment. The first ring inFIG. 20Bis considered to be derived from the (010) plane, the (100) plane, and the like of the InGaZnO4crystal. The second ring inFIG. 20Bis considered to be derived from the (110) plane and the like.

As described above, the CAAC-OS is an oxide semiconductor with high crystallinity. Entry of impurities, formation of defects, or the like might decrease the crystallinity of an oxide semiconductor. This means that the CAAC-OS has negligible amounts of impurities and defects (e.g., oxygen vacancies).

The characteristics of an oxide semiconductor having impurities or defects might be changed by light, heat, or the like. Impurities contained in the oxide semiconductor might serve as carrier traps or carrier generation sources, for example. Furthermore, oxygen vacancies in the oxide semiconductor might serve as carrier traps or carrier generation sources when hydrogen is trapped therein.

The CAAC-OS having small amounts of impurities and oxygen vacancies is an oxide semiconductor with low carrier density (specifically, lower than 8×1011/cm3, preferably lower than 1×1011/cm3, more preferably lower than 1×1010/cm3, and higher than or equal to 1×10−9/cm3). Such an oxide semiconductor is referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor. The CAAC-OS has a low impurity concentration and a low density of defect states. Thus, the CAAC-OS can be referred to as an oxide semiconductor having stable characteristics.

An nc-OS has a region where a crystal part is observed and a region where a crystal part is not clearly observed in a high-resolution TEM image. In most cases, the size of a crystal part included in the nc-OS is greater than or equal to 1 nm and less than or equal to 10 nm, or greater than or equal to 1 nm and less than or equal to 3 nm. An oxide semiconductor including a crystal part whose size is greater than 10 nm and less than or equal to 100 nm can be referred to as a microcrystalline oxide semiconductor. In a high-resolution TEM image of the nc-OS, for example, a grain boundary is not clearly observed in some cases. Note that there is a possibility that the origin of the nanocrystal is the same as that of a crystal part in a CAAC-OS.

In the nc-OS, a microscopic region (for example, a region with a size of greater than or equal to 1 nm and less than or equal to 10 nm, in particular, a region with a size of greater than or equal to 1 nm and less than or equal to 3 nm) has a periodic atomic arrangement. There is no regularity of crystal orientation between different crystal parts in the nc-OS. Thus, the orientation of the whole film is not observed. Accordingly, the nc-OS cannot be distinguished from an a-like OS or an amorphous oxide semiconductor, depending on an analysis method. For example, when the nc-OS is analyzed by an out-of-plane method using an X-ray beam having a diameter larger than the diameter of a crystal part, a peak that shows a crystal plane does not appear. Furthermore, a halo pattern is shown in an electron diffraction pattern of the nc-OS obtained by using an electron beam having a probe diameter larger than the diameter of a crystal part (e.g., larger than or equal to 50 nm). Meanwhile, spots are shown in a nanobeam electron diffraction pattern of the nc-OS obtained by using an electron beam having a probe diameter close to, or smaller than the diameter of a crystal part. Moreover, in a nanobeam electron diffraction pattern of the nc-OS, regions with high luminance in a circular (ring) pattern are shown in some cases. Also in a nanobeam electron diffraction pattern of the nc-OS, a plurality of spots are shown in a ring-like region in some cases.

Since there is no regularity of crystal orientation between the crystal parts (nanocrystals) as mentioned above, the nc-OS can also be referred to as an oxide semiconductor including random aligned nanocrystals (RANC) or an oxide semiconductor including non-aligned nanocrystals (NANC).

The nc-OS is an oxide semiconductor that has high regularity as compared with an amorphous oxide semiconductor. Therefore, the nc-OS is likely to have a lower density of defect states than an a-like OS and an amorphous oxide semiconductor. However, there is no regularity of crystal orientation between different crystal parts in the nc-OS. Therefore, the nc-OS has a higher density of defect states than the CAAC-OS.

An a-like OS has a structure intermediate between those of the nc-OS and the amorphous oxide semiconductor.

In a high-resolution TEM image of the a-like OS, a void may be observed. Furthermore, in the high-resolution TEM image, there are a region where a crystal part is clearly observed and a region where a crystal part is not observed.

The a-like OS has an unstable structure because it contains a void. To verify that the a-like OS has an unstable structure as compared with a CAAC-OS and an nc-OS, change in structure caused by electron irradiation is described below.

An a-like OS (sample A), an nc-OS (sample B), and a CAAC-OS (sample C) are prepared as samples subjected to electron irradiation. Each of the samples is an In—Ga—Zn oxide.

Note that which part is regarded as a crystal part is determined as follows. It is known that a unit cell of the InGaZnO4crystal has a structure in which nine layers including three In—O layers and six Ga—Zn—O layers are stacked in the c-axis direction. The spacing between these adjacent layers is equivalent to the lattice spacing on the (009) plane (also referred to as d value). The value is calculated to 0.29 nm from crystal structure analysis. Accordingly, a portion where the lattice spacing between lattice fringes is greater than or equal to 0.28 nm and less than or equal to 0.30 nm is regarded as a crystal part of InGaZnO4. Each of lattice fringes corresponds to the a-b plane of the InGaZnO4crystal.

FIG. 21shows change in the average size of crystal parts (at 22 points to 45 points) in each sample. Note that the crystal part size corresponds to the length of a lattice fringe.FIG. 21indicates that the crystal part size in the a-like OS increases with an increase in the cumulative electron dose. Specifically, as shown by (1) inFIG. 21, a crystal part of approximately 1.2 nm (also referred to as an initial nucleus) at the start of TEM observation grows to a size of approximately 2.6 nm at a cumulative electron dose of 4.2×108e−/nm2. In contrast, the crystal part size in the nc-OS and the CAAC-OS shows little change from the start of electron irradiation to a cumulative electron dose of 4.2×108e−/nm2. Specifically, as shown by (2) and (3) inFIG. 21, the average crystal sizes in the nc-OS and the CAAC-OS are approximately 1.4 nm and approximately 2.1 nm, respectively, regardless of the cumulative electron dose.

In this manner, growth of the crystal part in the a-like OS is induced by electron irradiation. In contrast, in the nc-OS and the CAAC-OS, growth of the crystal part is hardly induced by electron irradiation. Therefore, the a-like OS has an unstable structure as compared with the nc-OS and the CAAC-OS.

For example, in the case of an oxide semiconductor having an atomic ratio of In:Ga:Zn=1:1:1, the density of single crystal InGaZnO4with a rhombohedral crystal structure is 6.357 g/cm3. Accordingly, in the case of the oxide semiconductor having an atomic ratio of In:Ga:Zn=1:1:1, the density of the a-like OS is higher than or equal to 5.0 g/cm3and lower than 5.9 g/cm3. For example, in the case of the oxide semiconductor having an atomic ratio of In:Ga:Zn=1:1:1, the density of each of the nc-OS and the CAAC-OS is higher than or equal to 5.9 g/cm3and lower than 6.3 g/cm3.

Note that a single crystal oxide semiconductor with the same composition does not exist in some cases. In that case, single crystal oxide semiconductors with different compositions are combined at an adequate ratio, which makes it possible to calculate density equivalent to that of a single crystal oxide semiconductor with a desired composition. The density of a single crystal oxide semiconductor with a desired composition can be calculated using a weighted average according to the combination ratio of the single crystal oxide semiconductors with different compositions. Note that it is preferable to use as few kinds of single crystal oxide semiconductors as possible to calculate the density.

As described above, oxide semiconductors have various structures and various properties. Note that an oxide semiconductor may be a stacked layer including two or more of an amorphous oxide semiconductor, an a-like OS, an nc-OS, and a CAAC-OS, for example.

In this embodiment, a structural example of a semiconductor device including the transistor of one embodiment of the present invention will be described with reference to the drawings.

FIG. 22Ais a cross-sectional view of a semiconductor device of one embodiment of the present invention. The semiconductor device illustrated inFIG. 22Aincludes a transistor2200including a first semiconductor material in a lower portion and a transistor2100including a second semiconductor material in an upper portion. A cross-sectional view of the transistors in the channel length direction is on the left side of the dashed-dotted line, and a cross-sectional view of the transistors in the channel width direction is on the right side of the dashed-dotted line.

Note that the transistor2100may be provided with a back gate.

The first and second semiconductor materials preferably have different energy gaps. For example, the first semiconductor material can be a semiconductor material other than an oxide semiconductor (examples of such a semiconductor material include silicon (including strained silicon), germanium, silicon germanium, silicon carbide, gallium arsenide, aluminum gallium arsenide, indium phosphide, gallium nitride, and an organic semiconductor), and the second semiconductor material can be an oxide semiconductor. A transistor including a material other than an oxide semiconductor, such as single crystal silicon, can operate at high speed easily. On the other hand, a transistor including an oxide semiconductor has a small off-state current.

The transistor2200may be either an n-channel transistor or a p-channel transistor, and an appropriate transistor may be used in accordance with a circuit. Furthermore, the specific structure of the semiconductor device, such as the material or the structure used for the semiconductor device, is not necessarily limited to those described here except for the use of the transistor of one embodiment of the present invention which includes an oxide semiconductor.

FIG. 22Aillustrates a structure in which the transistor2100is provided over the transistor2200with an insulating film2201and an insulating film2207provided therebetween. A plurality of wirings2202are provided between the transistor2200and the transistor2100. Furthermore, wirings and electrodes provided over and under the insulating films are electrically connected to each other through a plurality of plugs2203embedded in the insulating films. In addition, an interlayer insulating film2204covering the transistor2100is provided.

The stack of the two kinds of transistors reduces the area occupied by the circuit, allowing a plurality of circuits to be highly integrated.

In the case where a silicon-based semiconductor material is used for the transistor2200provided in the lower portion, hydrogen in an insulating film provided in the vicinity of the semiconductor film of the transistor2200terminates dangling bonds of silicon; accordingly, the reliability of the transistor2200can be improved. Meanwhile, in the case where an oxide semiconductor is used for the transistor2100provided in the upper portion, hydrogen in an insulating film provided in the vicinity of the semiconductor film of the transistor2100becomes a factor of generating carriers in the oxide semiconductor; thus, the reliability of the transistor2100might be decreased. Therefore, in the case where the transistor2100including an oxide semiconductor is provided over the transistor2200including a silicon-based semiconductor material, it is particularly effective that the insulating film2207having a function of preventing diffusion of hydrogen is provided between the transistors2100and2200. The insulating film2207makes hydrogen remain in the lower portion, thereby improving the reliability of the transistor2200. In addition, since the insulating film2207suppresses diffusion of hydrogen from the lower portion to the upper portion, the reliability of the transistor2100can also be improved.

Furthermore, a blocking film having a function of preventing entry of hydrogen may be formed over the transistor2100so as to cover the transistor2100including an oxide semiconductor film. For the blocking film, a material that is similar to that of the insulating film2207can be used, and in particular, aluminum oxide is preferably used. The aluminum oxide film has a high shielding (blocking) effect of preventing penetration of both oxygen and impurities, such as hydrogen and moisture. Thus, by using the aluminum oxide film as the blocking film covering the transistor2100, release of oxygen from the oxide semiconductor film included in the transistor2100and entry of water and hydrogen into the oxide semiconductor film can be prevented.

Note that the transistor2200can be a transistor of various types without being limited to a planar type transistor. For example, the transistor2200can be a fin-type transistor, a tri-gate transistor, or the like. An example of a cross-sectional view in that case is illustrated inFIG. 22D. An insulating film2212is provided over a semiconductor substrate2211. The semiconductor substrate2211includes a protruding portion with a thin tip (also referred to a fin). Note that an insulating film may be provided over the protruding portion. The insulating film serves as a mask for preventing the semiconductor substrate2211from being etched when the protruding portion is formed. Alternatively, the protruding portion does not necessarily have a thin tip; a cuboid-like protruding portion or a protruding portion with a thick tip can be used, for example. A gate insulating film2214is provided over the protruding portion of the semiconductor substrate2211, and a gate electrode2213is provided over the gate insulating film2214. Although the gate electrode2213has a single-layer structure in this embodiment, one embodiment of the present invention is not limited to this example, and the gate electrode2213may have a stacked-layer structure of two or more layers. Source and drain regions2215are formed in the semiconductor substrate2211. Note that here is illustrated an example in which the semiconductor substrate2211includes a protruding portion; however, the semiconductor device of one embodiment of the present invention is not limited thereto. For example, a semiconductor region including a protruding portion may be formed by processing an SOI substrate.

[Examples of Circuit Configuration]

In the above structure, electrodes of the transistors2100and2200can be connected in a variety of ways; thus, a variety of circuits can be formed. Examples of a circuit configuration which can be achieved by using the semiconductor device of one embodiment of the present invention are shown below.

A circuit diagram inFIG. 22Bshows a configuration of a “CMOS circuit” in which the p-channel transistor2200and the n-channel transistor2100are connected to each other in series and in which gates of them are connected to each other.

A circuit diagram inFIG. 22Cshows a configuration in which a source and a drain of the transistor2100are connected to a source and a drain of the transistor2200. With such a configuration, the transistors can function as a so-called analog switch.

FIG. 23is a cross-sectional view of a semiconductor device in which a CMOS circuit is formed using the transistor2200and a transistor2300each including a channel formed using the first semiconductor material.

The transistor2300includes impurity regions2301serving as source and drain regions, a gate electrode2303, a gate insulating film2304, and a sidewall insulating film2305. The transistor2300may also include an impurity region2302serving as an LDD region under the sidewall insulating film2305. The description forFIG. 22Acan be referred to for other components inFIG. 23.

The transistors2200and2300preferably have opposite polarities. For example, when the transistor2200is a p-channel transistor, the transistor2300is preferably an n-channel transistor.

A photoelectric conversion element, such as a photodiode, may be provided in the semiconductor devices illustrated inFIG. 22AandFIG. 23.

The photodiode can be formed using a single crystal semiconductor or a polycrystalline semiconductor. The photodiode formed using a single crystal semiconductor or a polycrystalline semiconductor is preferable because of its high light detection sensitivity.

FIG. 24Ais a cross-sectional view of a semiconductor device in which a substrate2001is provided with a photodiode2400. The photodiode2400includes a conductive film2401having a function as one of an anode and a cathode, a conductive film2402having a function as the other of the anode and the cathode, and a conductive film2403electrically connecting the conductive film2402and a plug2004. The conductive films2401to2403may be formed by injecting an impurity into the substrate2001.

Although the photodiode2400is provided so that a current flows in the vertical direction with respect to the substrate2001inFIG. 24A, the photodiode2400may be provided so that a current flows in the lateral direction with respect to the substrate2001.

FIG. 24Bis a cross-sectional view of a semiconductor device in which a photodiode2500is provided over the transistor2100. The photodiode2500includes a conductive film2501having a function as one of an anode and a cathode, a conductive film2502having a function as the other of the anode and the cathode, and a semiconductor layer2503. The photodiode2500is electrically connected to the transistor2100through a plug2504.

InFIG. 24B, the photodiode2500may also be provided at the same level as the transistor2100. Alternatively, the photodiode2500may also be provided at the level between the transistor2200and the transistor2100.

The description forFIG. 22AandFIG. 23can be referred to for the details of other components inFIGS. 24A and 24B.

The photodiode2400or the photodiode2500may be formed using a material capable of generating charge by absorbing a radiation. Examples of a material capable of generating charge by absorbing a radiation include selenium, lead iodide, mercury iodide, gallium arsenide, CdTe, and CdZn.

The use of selenium for the photodiode2400or the photodiode2500can provide a photoelectric conversion element having a light absorption coefficient in a wide wavelength range of visible light, ultraviolet light, X-rays, and gamma rays, for example.

An example of a semiconductor device (memory device) which includes the transistor of one embodiment of the present invention, which can hold stored data even when not powered, and which has an unlimited number of write cycles is illustrated inFIG. 25.

A semiconductor device illustrated inFIG. 25is different from the memory device described in Embodiment 1 in that the transistor100is not provided. Also in that case, writing and holding of data can be performed in a manner similar to the above.

Next, reading of data in the semiconductor device shown inFIG. 25is described. When a transistor200is turned on, a wiring3003which is in a floating state and a capacitor300are electrically connected to each other, and charge is redistributed between the wiring3003and the capacitor300. As a result, the potential of the wiring3003is changed. The amount of change in potential of the wiring3003varies depending on the potential of one electrode of the capacitor300(or charge accumulated in the capacitor300).

For example, the potential of the wiring3003after the charge redistribution is (CB×VB0+C×V)/(CB+C), where V is the potential of the one electrode of the capacitor300, C is the capacitance of the capacitor300, CBis the capacitance component of the wiring3003, and VB0is the potential of the wiring3003before the charge redistribution. Thus, it can be found that, assuming that a memory cell is in either of two states in which the potential of the one electrode of the capacitor300is V1and V0(V1>V0), the potential of the wiring3003in the case of holding the potential V1(=(CB×VB0+C×V1)/(CB+C)) is higher than the potential of the wiring3003in the case of holding the potential V0(=(CB×VB0+C×V0)/(CB+C)).

Then, by comparing the potential of the wiring3003with a predetermined potential, data can be read.

In that case, a transistor including a first semiconductor material may be used for a driver circuit for driving the memory cell, and a transistor including a second semiconductor material may be stacked over the driver circuit as the transistor200.

When a transistor including a channel formation region formed using an oxide semiconductor and having an extremely small off-state current is applied to the semiconductor device in this embodiment, the semiconductor device can hold stored data for an extremely long time. In other words, power consumption can be sufficiently reduced because the refresh operation becomes unnecessary or the frequency of refresh operations can be extremely low. Moreover, stored data can be held for a long time even when power is not supplied (note that a potential is preferably fixed).

Furthermore, in the semiconductor device described in this embodiment, high voltage is not needed for writing data and there is no problem, such as deterioration of elements. For example, unlike a conventional nonvolatile memory, it is not necessary to inject and extract electrons into and from a floating gate, and thus, a problem, such as deterioration of a gate insulating film, does not arise at all. In other words, the semiconductor device of one embodiment of the disclosed invention does not have a limit on the number of times of writing, which is a problem in a conventional nonvolatile memory, and reliability thereof is drastically improved. Furthermore, data is written depending on the on state and the off state of the transistor, whereby high-speed operation can be easily achieved.

The memory device described in this embodiment can also be used in an LSI, such as a central processing unit (CPU), a digital signal processor (DSP), a custom LSI, or a programmable logic device (PLD) and a radio frequency identification (RF-ID) tag, for example.

In this embodiment, an RF device tag that includes any of the transistors and the memory devices described in the above embodiments will be described with reference toFIG. 26.

The RF device tag of this embodiment includes a memory circuit, stores necessary data for the memory circuit, and transmits and receives data to and from the outside by using contactless means, for example, wireless communication. With these features, the RF device tag can be used for an individual authentication system in which an object or the like is recognized by reading its individual information, for example. In order that the RF device tag is used for such application, extremely high reliability is needed.

The configuration of the RF device tag is described with reference toFIG. 26.FIG. 26is a block diagram showing a configuration example of the RF device tag.

As shown inFIG. 26, an RF device tag800includes an antenna804that receives a radio signal803that is transmitted from an antenna802connected to a communication device801(also referred to as an interrogator, a reader/writer, or the like). The RF device tag800includes a rectifier circuit805, a constant voltage circuit806, a demodulation circuit807, a modulation circuit808, a logic circuit809, a memory circuit810, and a ROM811. A transistor having a rectifying function included in the demodulation circuit807may be formed using a material which enables a reverse current to be small enough, for example, an oxide semiconductor. This can suppress the phenomenon of a rectifying function becoming weaker due to generation of a reverse current and prevent saturation of the output from the demodulation circuit. In other words, the input to the demodulation circuit and the output from the demodulation circuit can have a relation closer to a linear relation. Note that data transmission methods are roughly classified into the following three methods: an electromagnetic coupling method by which a pair of coils is provided so as to face each other and communicates with each other by mutual induction, an electromagnetic induction method by which communication is performed using an induction field, and an electric wave method by which communication is performed using an electric wave. Any of these methods can be used in the RF device tag800described in this embodiment.

Next, the configuration of each circuit is described. The antenna804exchanges the radio signal803with the antenna802that is connected to the communication device801. The rectifier circuit805generates an input potential by rectification, for example, half-wave voltage doubler rectification, of an input alternating signal generated by reception of a radio signal at the antenna804and smoothing of the rectified signal with a capacitor provided in a later stage. Note that a limiter circuit may be provided on an input side or an output side of the rectifier circuit805. The limiter circuit controls power so that power which is higher than or equal to a certain power is not input to a circuit in a later stage if the amplitude of the input alternating signal is high and an internal generation voltage is high.

The constant voltage circuit806generates a stable power supply voltage from an input potential and supplies it to each circuit. Note that the constant voltage circuit806may include a reset signal generation circuit. The reset signal generation circuit is a circuit which generates a reset signal of the logic circuit809by utilizing rise of the stable power supply voltage.

The demodulation circuit807demodulates the input alternating signal by envelope detection and generates a demodulated signal. Furthermore, the modulation circuit808performs modulation in accordance with data output from the antenna804.

The logic circuit809analyzes and processes the demodulated signal. The memory circuit810holds the input data and includes a row decoder, a column decoder, a memory region, and the like. The ROM811stores an identification number (ID) or the like and outputs it in accordance with processing.

Note that whether each circuit as described above is provided can be determined as appropriate and as needed.

Any of the memory devices described in the above embodiments can be used for the memory circuit810. Since the memory device of one embodiment of the present invention can hold data even when not powered, the memory device can be favorably used for the RF device tag. In addition, the memory device of one embodiment of the present invention needs much less power (voltage) for data writing than a conventional nonvolatile memory; thus, it is possible to prevent a difference between the maximum communication range in data reading and that in data writing. Furthermore, it is possible to suppress malfunction or incorrect writing which is caused by power shortage in data writing.

Since the memory device of one embodiment of the present invention can be used for a nonvolatile memory, it can also be used for the ROM811. In that case, it is preferable that a manufacturer separately prepare a command for writing data to the ROM811so that a user cannot rewrite data freely. The manufacturer gives identification numbers before shipment and then starts shipment of products, instead of putting identification numbers to all the manufactured RF device tags; thus, it is possible to put identification numbers only to good products to be shipped. Therefore, the identification numbers of the shipped products are in series and customer management corresponding to the shipped products is easily performed.

In this embodiment, a CPU will be described, which includes at least any of the transistors described in the above embodiments and any of the memory devices described in the above embodiments.

FIG. 27is a block diagram showing a configuration example of a CPU which includes at least any of the transistors described in the above embodiments as a component.

The CPU shown inFIG. 27includes, over a substrate1190, an arithmetic logic unit (ALU)1191, an ALU controller1192, an instruction decoder1193, an interrupt controller1194, a timing controller1195, a register1196, a register controller1197, a bus interface1198(BUS I/F), a rewritable ROM1199, and a ROM interface (ROM I/F)1189. A semiconductor substrate, an SOI substrate, a glass substrate, or the like is used as the substrate1190. The ROM1199and the ROM interface1189may each be provided over a separate chip. Needless to say, the CPU shown inFIG. 27is just an example with a simplified configuration, and an actual CPU may have a variety of configurations depending on the application. For example, the CPU may have the following configuration: a structure including the CPU shown inFIG. 27or an arithmetic circuit is considered as one core, a plurality of the cores are included, and the cores operate in parallel. The number of bits that the CPU can process in an internal arithmetic circuit or in a data bus can be8,16,32, or64, for example.

The timing controller1195generates signals for controlling operation timings of the ALU1191, the ALU controller1192, the instruction decoder1193, the interrupt controller1194, and the register controller1197. For example, the timing controller1195includes an internal clock generator for generating an internal clock signal CLK2on the basis of a reference clock signal CLK1and supplies the internal clock signal CLK2to the above circuits.

In the CPU shown inFIG. 27, a memory cell is provided in the register1196. For the memory cell of the register1196, any of the transistors described in the above embodiments can be used.

In the CPU shown inFIG. 27, the register controller1197selects an operation of holding data in the register1196in accordance with an instruction from the ALU1191. That is, the register controller1197selects whether data is held by a flip-flop or by a capacitor in the memory cell included in the register1196. When data holding by the flip-flop is selected, a power supply voltage is supplied to the memory cell in the register1196. When data holding by the capacitor is selected, the data is rewritten in the capacitor, and supply of a power supply voltage to the memory cell in the register1196can be stopped.

FIG. 28is an example of a circuit diagram of a memory element that can be used as the register1196. A memory element1200includes a circuit1201in which stored data is volatile when power supply is stopped, a circuit1202in which stored data is nonvolatile even when power supply is stopped, a switch1203, a switch1204, a logic element1206, a capacitor1207, and a circuit1220having a selecting function. The circuit1202includes a capacitor1208, a transistor1209, and a transistor1210. Note that the memory element1200may further include another element, such as a diode, a resistor, or an inductor, as necessary.

Any of the memory devices described in the above embodiments can be used as the circuit1202. When supply of a power supply voltage to the memory element1200is stopped, a ground potential (0 V) or a potential at which the transistor1209in the circuit1202is turned off continues to be input to a gate electrode of the transistor1209. For example, the gate electrode of the transistor1209is grounded through a load, such as a resistor.

Shown here is an example in which the switch1203is a transistor1213having one conductivity type (e.g., an n-channel transistor) and the switch1204is a transistor1214having a conductivity type opposite to the one conductivity type (e.g., a p-channel transistor). A first terminal of the switch1203corresponds to one of a source electrode and a drain electrode of the transistor1213, a second terminal of the switch1203corresponds to the other of the source electrode and the drain electrode of the transistor1213, and conduction or non-conduction between the first terminal and the second terminal of the switch1203(i.e., the on/off state of the transistor1213) is selected by a control signal RD input to a gate electrode of the transistor1213. A first terminal of the switch1204corresponds to one of a source electrode and a drain electrode of the transistor1214, a second terminal of the switch1204corresponds to the other of the source electrode and the drain electrode of the transistor1214, and conduction or non-conduction between the first terminal and the second terminal of the switch1204(i.e., the on/off state of the transistor1214) is selected by the control signal RD input to a gate electrode of the transistor1214.

One of a source electrode and a drain electrode of the transistor1209is electrically connected to one of a pair of electrodes of the capacitor1208and a gate electrode of the transistor1210. Here, the connection portion is referred to as a node M2. One of a source electrode and a drain electrode of the transistor1210is electrically connected to a wiring which can supply a low power supply potential (e.g., a GND line), and the other thereof is electrically connected to the first terminal of the switch1203(the one of the source electrode and the drain electrode of the transistor1213). The second terminal of the switch1203(the other of the source electrode and the drain electrode of the transistor1213) is electrically connected to the first terminal of the switch1204(the one of the source electrode and the drain electrode of the transistor1214). The second terminal of the switch1204(the other of the source electrode and the drain electrode of the transistor1214) is electrically connected to a wiring which can supply a power supply potential VDD. The second terminal of the switch1203(the other of the source electrode and the drain electrode of the transistor1213), the first terminal of the switch1204(the one of the source electrode and the drain electrode of the transistor1214), an input terminal of the logic element1206, and one of a pair of electrodes of the capacitor1207are electrically connected to each other. Here, the connection portion is referred to as a node M1. The other of the pair of electrodes of the capacitor1207can be supplied with a constant potential. For example, the other of the pair of electrodes of the capacitor1207can be supplied with a low power supply potential (e.g., GND) or a high power supply potential (e.g., VDD). The other of the pair of electrodes of the capacitor1207is electrically connected to the wiring which can supply a low power supply potential (e.g., the GND line). The other of the pair of electrodes of the capacitor1208can be supplied with a constant potential. For example, the other of the pair of electrodes of the capacitor1208can be supplied with a low power supply potential (e.g., GND) or a high power supply potential (e.g., VDD). The other of the pair of electrodes of the capacitor1208is electrically connected to the wiring which can supply a low power supply potential (e.g., the GND line).

The capacitor1207and the capacitor1208are not necessarily provided when the parasitic capacitance or the like of the transistor or the wiring is utilized.

A control signal WE is input to a first gate electrode of the transistor1209. As for each of the switch1203and the switch1204, a conduction state or a non-conduction state between the first terminal and the second terminal is selected by the control signal RD which is different from the control signal WE. When one of the switches is in the conduction state between the first terminal and the second terminal, the other of the switches is in the non-conduction state between the first terminal and the second terminal

A signal corresponding to data held in the circuit1201is input to the other of the source electrode and the drain electrode of the transistor1209.FIG. 28shows an example in which a signal output from the circuit1201is input to the other of the source electrode and the drain electrode of the transistor1209. The logic value of a signal output from the second terminal of the switch1203(the other of the source electrode and the drain electrode of the transistor1213) is inverted by the logic element1206, and the inverted signal is input to the circuit1201through the circuit1220.

InFIG. 28, a signal output from the second terminal of the switch1203(the other of the source electrode and the drain electrode of the transistor1213) is input to the circuit1201through the logic element1206and the circuit1220; however, one embodiment of the present invention is not limited thereto. The signal output from the second terminal of the switch1203(the other of the source electrode and the drain electrode of the transistor1213) may be input to the circuit1201without its logic value being inverted. For example, in the case where the circuit1201includes a node at which a signal obtained by inverting the logic value of a signal input from the input terminal is held, the signal output from the second terminal of the switch1203(the other of the source electrode and the drain electrode of the transistor1213) can be input to the node.

InFIG. 28, the transistors included in the memory element1200except for the transistor1209can each be a transistor in which a channel is formed in a layer formed using a semiconductor other than an oxide semiconductor or in the substrate1190. For example, the transistor can be a transistor in which a channel is formed in a silicon layer or a silicon substrate. Alternatively, all the transistors in the memory element1200may each be a transistor in which a channel is formed in an oxide semiconductor film. Further alternatively, the memory element1200may include, besides the transistor1209, a transistor in which a channel is formed in an oxide semiconductor film; for the other transistors, a transistor in which a channel is formed in a layer formed using a semiconductor other than an oxide semiconductor or in the substrate1190can be used.

As the circuit1201shown inFIG. 28, for example, a flip-flop circuit can be used. As the logic element1206, for example, an inverter or a clocked inverter can be used.

In the semiconductor device of one embodiment of the present invention, in a period during which the memory element1200is not supplied with a power supply voltage, data stored in the circuit1201can be held by the capacitor1208which is provided in the circuit1202.

The off-state current of a transistor in which a channel is formed in an oxide semiconductor film is extremely small. For example, the off-state current of a transistor in which a channel is formed in an oxide semiconductor film is much smaller than that of a transistor in which a channel is formed in silicon having crystallinity. Thus, when the transistor is used as the transistor1209, a signal held in the capacitor1208is held for a long time also in a period during which a power supply voltage is not supplied to the memory element1200. The memory element1200can accordingly hold the stored content (data) also in a period during which the supply of a power supply voltage is stopped.

Since the above-described memory element performs pre-charge operation with the switch1203and the switch1204, the time required for the circuit1201to hold original data again after the supply of a power supply voltage is restarted can be shortened.

In the circuit1202, a signal held by the capacitor1208is input to the gate electrode of the transistor1210. Therefore, after the supply of a power supply voltage to the memory element1200is restarted, the signal held by the capacitor1208can be converted into the one corresponding to the state (the on state or the off state) of the transistor1210to be read from the circuit1202. Consequently, an original signal can be accurately read even when the potential corresponding to the signal held by the capacitor1208varies to some degree.

By applying the above-described memory element1200to a memory device, such as a register or a cache memory, included in a processor, data in the memory device can be prevented from being lost owing to the stop of the supply of a power supply voltage. Furthermore, shortly after the supply of a power supply voltage is restarted, the memory can be returned to the state before the stop of the power supply. Therefore, the power supply can be stopped even for a short time in the processor or one or a plurality of logic circuits included in the processor. Accordingly, power consumption can be suppressed.

Although the memory element1200is used in a CPU in this embodiment, the memory element1200can also be used in an LSI, such as a digital signal processor (DSP), a custom LSI, or a programmable logic device (PLD), and a radio frequency identification (RF-ID) tag.

In this embodiment, a display device of one embodiment of the present invention will be described with reference toFIGS. 29A to 29CandFIGS. 30A and 30B.

Examples of a display element provided in the display device include a liquid crystal element (also referred to as a liquid crystal display element) and a light-emitting element (also referred to as a light-emitting display element). The light-emitting element includes, in its category, an element whose luminance is controlled by current or voltage and specifically includes, in its category, an inorganic electroluminescent (EL) element, an organic EL element, and the like. A display device including an EL element (an EL display device) and a display device including a liquid crystal element (a liquid crystal display device) are described below as examples of the display device.

Note that the display device described below includes, in its category, a panel in which a display element is sealed and a module in which an IC, such as a controller, or the like is mounted on the panel.

The display device described below refers to an image display device or a light source (including a lighting device). The display device includes, in its category, any of the following modules: a module provided with a connector, such as an FPC or TCP, a module in which a printed wiring board is provided at the end of TCP, and a module in which an integrated circuit (IC) is mounted directly on a display element by a COG method.

FIGS. 29A to 29Cillustrate an example of an EL display device of one embodiment of the present invention.FIG. 29Ais a circuit diagram of a pixel in the EL display device.FIG. 29Bis a top view illustrating the whole EL display device.FIG. 29Cis a cross-sectional view taken along part of dashed-dotted line M-N inFIG. 29B.

FIG. 29Ashows an example of a circuit diagram of a pixel used in the EL display device.

Note that in this specification and the like, it might be possible for those skilled in the art to constitute one embodiment of the invention even when portions to which all the terminals of an active element (e.g., a transistor or a diode), a passive element (e.g., a capacitor or a resistor), or the like are connected are not specified. In other words, one embodiment of the invention can be clear even when connection portions are not specified. Furthermore, in the case where a connection portion is disclosed in this specification and the like, it can be determined that one embodiment of the invention in which a connection portion is not specified is disclosed in this specification and the like. Particularly in the case where the number of portions to which a terminal is connected might be plural, it is not necessary to specify the portions to which the terminal is connected. Therefore, it might be possible to constitute one embodiment of the invention by specifying only portions to which some of terminals of an active element (e.g., a transistor or a diode), a passive element (e.g., a capacitor or a resistor), or the like are connected.

Note that in this specification and the like, it might be possible for those skilled in the art to specify the invention when at least a connection portion of a circuit is specified. Alternatively, it might be possible for those skilled in the art to specify the invention when at least a function of a circuit is specified. In other words, when a function of a circuit is specified, one embodiment of the invention can be clear. Furthermore, it can be determined that one embodiment of the invention whose function is specified is disclosed in this specification and the like. Alternatively, when a connection portion of a circuit is specified, the circuit is disclosed as one embodiment of the invention even when its function is not specified, and one embodiment of the invention can be constituted. Alternatively, when a function of a circuit is specified, the circuit is disclosed as one embodiment of the invention even when its connection portion is not specified, and one embodiment of the invention can be constituted.

The EL display device shown inFIG. 29Aincludes a switching element743, a transistor741, a capacitor742, and a light-emitting element719.

FIG. 29Ashows one example of a circuit configuration; therefore, a transistor can be provided additionally. In contrast, for each node inFIG. 29A, it is possible not to provide an additional transistor, switch, passive element, or the like.

A gate electrode of the transistor741is electrically connected to a first terminal of the switching element743and one electrode of the capacitor742. A source electrode of the transistor741is electrically connected to the other electrode of the capacitor742and one electrode of the light-emitting element719. A power supply potential VDD is supplied to a drain electrode of the transistor741. A second terminal of the switching element743is electrically connected to a signal line744. A constant potential is supplied to the other electrode of the light-emitting element719. The constant potential is a ground potential GND or a potential lower than the ground potential GND.

It is preferable to use a transistor as the switching element743. When the transistor is used as the switching element, the area of the pixel can be reduced, so that the EL display device can have high resolution. As the switching element743, a transistor formed through the same process as the transistor741can be used, so that the EL display device can be manufactured with high productivity. Note that as the transistor741and/or the switching element743, any of the above-described transistors can be used, for example.

FIG. 29Bis a top view of the EL display device. The EL display device includes a substrate700, a substrate750, a sealant734, a driver circuit735, a driver circuit736, a pixel737, and an FPC732. The sealant734is provided between the substrate700and the substrate750so as to surround the pixel737, the driver circuit735, and the driver circuit736. Note that the driver circuit735and/or the driver circuit736may be provided outside the sealant734.

FIG. 29Cis a cross-sectional view of the EL display device taken along part of dashed-dotted line M-N inFIG. 29B.

FIG. 29Cillustrates the structure of the transistor741including an insulator712over the substrate700, semiconductors706aand706bover the insulator712, conductors716aand716bin contact with the semiconductors706aand706b, a semiconductor706cand an insulator718over the semiconductor706band the conductor716aand716b, and conductors714aand714bthat are provided over the insulator718and overlap with the semiconductor706c. Note that the structure of the transistor741is just an example; the transistor741may have a structure different from that illustrated inFIG. 29C.

In the transistor741illustrated inFIG. 29C, the conductors714aand714bserve as a gate electrode, the insulator718serves as a gate insulator, the conductor716aserves as a source electrode, and the conductor716bserves as a drain electrode.

InFIG. 29C, a capacitor having a structure similar to that of the capacitor300, which is described in the above embodiment and is a three-dimensional capacitor, can be used as the capacitor742. Accordingly, the capacitance of the capacitor per projected area can be increased, leading to a smaller area, higher integration, and miniaturization of the EL display device.

The capacitor742can be formed using a film that is also used for the transistor741. The conductor716aand a first electrode of the capacitor742are preferably formed using the same kind of conductor, in which case the conductor716aand the first electrode of the capacitor742can be formed through the same step. The conductors714aand714band a second electrode of the capacitor742are preferably formed using the same kind of conductor, in which case the conductors714aand714band the second electrode of the capacitor742can be formed through the same step.

The capacitor742illustrated inFIG. 29Chas a large capacitance per area. Therefore, the EL display device illustrated inFIG. 29Chas high display quality.

An insulator720is provided over the transistor741and the capacitor742. The insulator720may have an opening reaching the conductor716athat serves as a source electrode of the transistor741. A conductor781is provided over the insulator720. The conductor781may be electrically connected to the transistor741through the opening in the insulator720.

A partition wall784having an opening reaching the conductor781is provided over the conductor781. A light-emitting layer782in contact with the conductor781in the opening provided in the partition wall784is provided over the partition wall784. A conductor783is provided over the light-emitting layer782. A region where the conductor781, the light-emitting layer782, and the conductor783overlap with each other serves as the light-emitting element719.

So far, an example of the EL display device has been described. Next, an example of a liquid crystal display device is described.

FIG. 30Ais a circuit diagram showing a configuration example of a pixel of a liquid crystal display device. A pixel illustrated inFIGS. 30A and 30Bincludes a transistor751, a capacitor752, and an element (liquid crystal element)753in which a space between a pair of electrodes is filled with a liquid crystal.

One of a source electrode and a drain electrode of the transistor751is electrically connected to a signal line755, and a gate electrode of the transistor751is electrically connected to a scan line754.

One electrode of the capacitor752is electrically connected to the other of the source electrode and the drain electrode of the transistor751, and the other electrode of the capacitor752is electrically connected to a wiring for supplying a common potential.

One electrode of the liquid crystal element753is electrically connected to the other of the source electrode and the drain electrode of the transistor751, and the other electrode of the liquid crystal element753is electrically connected to a wiring for supplying a common potential. The common potential supplied to the wiring electrically connected to the other electrode of the capacitor752may be different from that supplied to the wiring electrically connected to the other electrode of the liquid crystal element753.

Note that the description of the liquid crystal display device is made on the assumption that the top view of the liquid crystal display device is similar to that of the EL display device.FIG. 30Bis a cross-sectional view of the liquid crystal display device taken along dashed-dotted line M-N inFIG. 29B. InFIG. 30B, an FPC732is connected to a wiring733athrough a terminal731. Note that the wiring733amay be formed using the same kind of conductor as the conductor of the transistor751or using the same kind of semiconductor as the semiconductor of the transistor751.

For the transistor751, the description of the transistor741is referred to. For the capacitor752, the description of the capacitor742is referred to. Note that the structure of the capacitor752inFIG. 30Bcorresponds to, but is not limited to, the structure of the capacitor742inFIG. 29C.

Note that in the case where an oxide semiconductor is used as the semiconductor of the transistor751, the off-state current of the transistor751can be extremely small. Therefore, charge held in the capacitor752is unlikely to leak, so that the voltage applied to the liquid crystal element753can be maintained for a long time. Accordingly, the transistor751can be kept off in a period during which a moving image with few motions or a still image is displayed, whereby power for the operation of the transistor751can be saved in that period; accordingly, a liquid crystal display device with low power consumption can be provided. Furthermore, the area occupied by the capacitor752can be reduced; thus, a liquid crystal display device with a high aperture ratio or a high-resolution liquid crystal display device can be provided.

An insulator721is provided over the transistor751and the capacitor752. The insulator721has an opening reaching the transistor751. A conductor791is provided over the insulator721. The conductor791is electrically connected to the transistor751through the opening in the insulator721.

An insulator792serving as an alignment film is provided over the conductor791. A liquid crystal layer793is provided over the insulator792. An insulator794serving as an alignment film is provided over the liquid crystal layer793. A spacer795is provided over the insulator794. A conductor796is provided over the spacer795and the insulator794. A substrate797is provided over the conductor796.

With the above-described structure, a display device including a capacitor occupying a small area, a display device with high display quality, or a high-resolution display device can be provided.

For example, in this specification and the like, a display element, a display device which is a device including a display element, a light-emitting element, and a light-emitting device which is a device including a light-emitting element can employ various modes or can include various elements. For example, the display element, the display device, the light-emitting element, or the light-emitting device includes at least one of a light-emitting diode (LED) for white, red, green, blue, or the like, a transistor (a transistor that emits light depending on current), an electron emitter, a liquid crystal element, electronic ink, an electrophoretic element, a grating light valve (GLV), a plasma display panel (PDP), a display element using micro electro mechanical systems (MEMS), a digital micromirror device (DMD), a digital micro shutter (DMS), an interferometric modulator display (IMOD) element, a MEMS shutter display element, an optical-interference-type MEMS display element, an electrowetting element, a piezoelectric ceramic display, a display element including a carbon nanotube, and the like. Other than the above, display media whose contrast, luminance, reflectivity, transmittance, or the like is changed by electrical or magnetic effect may be included.

Note that examples of a display device including an EL element include an EL display. Examples of a display device including an electron emitter include a field emission display (FED) and an SED-type flat panel display (SED: surface-conduction electron-emitter display). Examples of a display device including a liquid crystal element include a liquid crystal display (e.g., a transmissive liquid crystal display, a transflective liquid crystal display, a reflective liquid crystal display, a direct-view liquid crystal display, or a projection liquid crystal display). Examples of a display device including electronic ink, Electronic Liquid Powder (registered trademark), or an electrophoretic element include electronic paper. In the case of a transflective liquid crystal display or a reflective liquid crystal display, some or all of pixel electrodes serve as reflective electrodes. For example, some or all of the pixel electrodes are formed to contain aluminum, silver, or the like. In such a case, a memory circuit, such as an SRAM, can be provided under the reflective electrodes, leading to lower power consumption.

Note that in the case of using an LED, graphene or graphite may be provided under an electrode or a nitride semiconductor of the LED. Graphene or graphite may be a multilayer film in which a plurality of layers are stacked. Providing graphene or graphite as described above enables easy formation of a nitride semiconductor thereover, such as an n-type GaN semiconductor including crystals. Furthermore, a p-type GaN semiconductor including crystals or the like can be provided thereover, and the LED can be thus formed. Note that an MN layer may be provided between the n-type GaN semiconductor including crystals and graphene or graphite. The GaN semiconductor included in the LED may be formed by MOCVD. When the graphene is provided, the GaN semiconductor included in the LED can also be formed by a sputtering method.

The semiconductor device of one embodiment of the present invention can be used for display devices, personal computers, image reproducing devices provided with recording media (typically, devices which reproduce the content of recording media, such as digital versatile discs (DVDs), and have displays for displaying the reproduced images), or the like. Other examples of an electronic device that can be equipped with the semiconductor device of one embodiment of the present invention are mobile phones, game machines including portable game consoles, portable data terminals, e-book readers, cameras, such as video cameras and digital still cameras, goggle-type displays (head mounted displays), navigation systems, audio reproducing devices (e.g., car audio systems and digital audio players), copiers, facsimiles, printers, multifunction printers, automated teller machines (ATM), and vending machines.FIGS. 31A to 31Fillustrate specific examples of such electronic devices.

FIG. 31Aillustrates a portable game console including a housing901, a housing902, a display portion903, a display portion904, a microphone905, a speaker906, an operation key907, a stylus908, and the like. Although the portable game console illustrated inFIG. 31Aincludes the two display portions903and904, the number of display portions included in the portable game console is not limited thereto.

FIG. 31Billustrates a portable data terminal including a first housing911, a second housing912, a first display portion913, a second display portion914, a joint915, an operation key916, and the like. The first display portion913is provided in the first housing911, and the second display portion914is provided in the second housing912. The first housing911and the second housing912are connected to each other with the joint915, and the angle between the first housing911and the second housing912can be changed with the joint915. An image displayed on the first display portion913may be switched depending on the angle between the first housing911and the second housing912at the joint915. A display device with a position input function may be used as at least one of the first display portion913and the second display portion914. Note that the position input function can be added by providing a touch panel in a display device. Alternatively, the position input function can be added by providing a photoelectric conversion element called a photosensor in a pixel portion of a display device.

FIG. 31Cillustrates a laptop personal computer including a housing921, a display portion922, a keyboard923, a pointing device924, and the like.

FIG. 31Dillustrates an electric refrigerator-freezer including a housing931, a refrigerator door932, a freezer door933, and the like.

FIG. 31Eillustrates a video camera including a first housing941, a second housing942, a display portion943, operation keys944, a lens945, a joint946, and the like. The operation keys944and the lens945are provided in the first housing941, and the display portion943is provided in the second housing942. The first housing941and the second housing942are connected to each other with the joint946, and the angle between the first housing941and the second housing942can be changed with the joint946. An image displayed on the display portion943may be switched depending on the angle between the first housing941and the second housing942at the joint946.

FIG. 31Fillustrates a car including a car body951, wheels952, a dashboard953, lights954, and the like.

In this embodiment, application examples of an RF device tag of one embodiment of the present invention will be described with reference toFIGS. 32A to 32F. The RF device tag is widely used and can be provided for, for example, products, such as bills, coins, securities, bearer bonds, documents (e.g., driver's licenses or resident's cards, seeFIG. 32A), recording media (e.g., DVD or video tapes, seeFIG. 32B), packaging containers (e.g., wrapping paper or bottles, seeFIG. 32C), vehicles (e.g., bicycles, seeFIG. 32D), personal belongings (e.g., bags or glasses), foods, plants, animals, human bodies, clothing, household goods, medical supplies, such as medicine and chemicals, and electronic devices (e.g., liquid crystal display devices, EL display devices, television sets, or mobile phones), or tags on the products (seeFIGS. 32E and 32F).

An RF device tag4000of one embodiment of the present invention is fixed to a product by being attached to a surface thereof or embedded therein. For example, the RF device tag4000is fixed to each product by being embedded in paper of a book, or embedded in an organic resin of a package. Since the RF device tag4000of one embodiment of the present invention can be reduced in size, thickness, and weight, it can be fixed to a product without spoiling the design of the product. Furthermore, bills, coins, securities, bearer bonds, documents, or the like can have an identification function by being provided with the RF device tag4000of one embodiment of the present invention, and the identification function can be utilized to prevent counterfeiting. Moreover, the efficiency of a system, such as an inspection system, can be improved by providing the RF device tag4000of one embodiment of the present invention for packaging containers, recording media, personal belongings, foods, clothing, household goods, electronic devices, or the like. Vehicles can also have higher security against theft or the like by being provided with the RF device tag4000of one embodiment of the present invention.

As described above, by using the RF device tag of one embodiment of the present invention for each application described in this embodiment, power for operation, such as writing or reading of data, can be reduced, which results in an increase in the maximum communication distance. Moreover, data can be held for an extremely long time even in the state where power is not supplied; thus, the RF device tag of one embodiment of the present invention can be preferably used for application in which data is not frequently written or read.

EXPLANATION OF REFERENCE

This application is based on Japanese Patent Application serial no. 2014-236230 filed with Japan Patent Office on Nov. 21, 2014, the entire contents of which are hereby incorporated by reference.