JP7490686B2 - Display device - Google Patents

Description

The invention disclosed in this specification relates to a semiconductor device and a method for driving the semiconductor device.

In recent years, flat panel displays such as liquid crystal displays have become widespread. In a display device such as a liquid crystal display, a transistor serving as a switching element, a liquid crystal element electrically connected to the transistor, and a storage capacitor connected in parallel to the liquid crystal element are provided in pixels arranged in row and column directions.

The semiconductor material constituting the semiconductor film included in the transistor is amorphous (
Silicon semiconductors such as amorphous silicon or polysilicon are widely used.

Metal oxides that exhibit semiconductor characteristics (hereinafter, referred to as oxide semiconductors) are semiconductor materials that can be used for semiconductor films included in transistors. For example, zinc oxide or In—Ga—
Techniques for manufacturing a transistor using a Zn-based oxide semiconductor have been disclosed (see Patent Documents 1 and 2).

In a display device, a storage capacitor has a dielectric film provided between a pair of electrodes, and at least one of the pair of electrodes is often formed of a conductive film having light-shielding properties, such as a gate electrode, a source electrode, or a drain electrode that constitutes a transistor.

The larger the capacitance value of the storage capacitor, the longer the period during which the alignment of the liquid crystal molecules in the liquid crystal element can be kept constant when an electric field is applied, which is expected to reduce the power consumption of the display device.

For example, in order to increase the charge capacity of the storage capacitor, there is a method of increasing the area occupied by the storage capacitor, specifically, the area where a pair of electrodes overlap. However, in the above-mentioned display device, if the area of the conductive film having light blocking properties is increased in order to increase the area where the pair of electrodes overlap, the aperture ratio of the pixel is reduced, and the display quality of the image is degraded.

In view of this, a technology has been disclosed that enables an increase in charge capacitance without reducing the aperture ratio by providing a light-transmitting storage capacitor formed using a light-transmitting material in a display device (see Patent Document 3).

JP 2007-123861 A JP 2007-96055 A U.S. Pat. No. 8,102,476

The storage capacitor of the display device disclosed in Patent Document 3 uses a light-transmitting semiconductor film for one electrode, a light-transmitting conductive film (specifically, a pixel electrode) for the other electrode, and a light-transmitting insulating film for the dielectric film. In addition, one electrode included in the storage capacitor is a thin film transistor (Thin Film Transistor) that is included in the display device and serves as a switching element.
The one electrode is formed of a channel layer (specifically, an oxide semiconductor) provided on a gate insulating layer of a thin film transistor (TFT). The oxide semiconductor used as the one electrode is an oxide semiconductor with increased electron density that can be used in a depression type TFT. The other electrode is a pixel electrode. In Patent Document 3, the range of the potential difference (voltage) between the common potential applied to the capacitance line connected to one electrode and the pixel potential applied to the pixel electrode is set to around 0 V, and the storage capacitor is operated.

When one electrode of a storage capacitor is made of an oxide semiconductor with increased electron density as in Patent Document 3, a TFT included in the display device and functioning as a switching element can be a depletion-type TFT in consideration of a manufacturing method of the display device. When a depletion-type transistor is used as a switching element, the threshold voltage of the transistor is lower than 0 V.

Generally, in a display device, the video data potential supplied to a display element is a potential within a potential amplitude centered on a common potential, and the common potential is often set to 0V.

As described above, a display device using a depletion-type TFT as a switching element and having a storage capacitor formed using an oxide semiconductor contained in the TFT as in Patent Document 3 requires a wider voltage range to drive the display device, resulting in a display device with increased power consumption. In addition, the TFT must be constantly supplied with a voltage in order to function as a switching element, which also leads to an increase in the power consumption of the display device.

In view of the above, one embodiment of the present invention is a semiconductor device including a light-transmitting storage capacitor including a light-transmitting semiconductor film, a light-transmitting conductive film, and a light-transmitting insulating film,
An object of the present invention is to provide a semiconductor device with reduced power consumption.

In addition, the storage capacitor described in Patent Document 3 is in a state where a positive bias is always applied to the other electrode, which is a conductive film having transparency, during its operation. Therefore, the threshold voltage of the storage capacitor fluctuates in the positive direction over time. Therefore, when the voltage range for operating the storage capacitor is near 0 V, the storage capacitor may not operate due to the change in the threshold voltage over time.

Therefore, it is significant to widen the operating range of a storage capacitor using an oxide semiconductor for one electrode.

In view of the above, one embodiment of the present invention is a semiconductor device including a light-transmitting storage capacitor including a light-transmitting semiconductor film, a light-transmitting conductive film, and a light-transmitting insulating film,
It is an object of the present invention to provide a driving method for stably operating the storage capacitor.

Another object of one embodiment of the present invention is to provide a semiconductor device in which a light-transmitting storage capacitor can operate stably.

In view of the above problems, one embodiment of the present invention includes an enhancement type transistor, a storage capacitor electrically connected to the transistor, a capacitance line electrically connected to the storage capacitor, and a display element electrically connected to the transistor and the storage capacitor, the storage capacitor includes a light-transmitting semiconductor film electrically connected to the capacitance line and functioning as one electrode, a light-transmitting conductive film included in the display element and functioning as the other electrode, and a dielectric film provided between the one electrode and the other electrode, and has a threshold voltage of 0 V or more. The storage capacitor includes
The semiconductor device is characterized in that the potential difference between the light-transmitting conductive film and the capacitance line is such that the light-transmitting semiconductor film is brought into a conductive state.

Another embodiment of the present invention includes an enhancement type transistor, a storage capacitor electrically connected to the transistor, a capacitance line electrically connected to the storage capacitor, and a display element electrically connected to the transistor and the storage capacitor. The storage capacitor is electrically connected to the capacitance line and includes a light-transmitting semiconductor film functioning as one electrode and a light-transmitting semiconductor film functioning as the other electrode.
The semiconductor device includes a light-transmitting conductive film included in a display element and a dielectric film provided between one electrode and the other electrode, has a threshold voltage of 0 V or more, and a storage capacitor operates with a potential difference between the light-transmitting conductive film and a capacitance line that is larger than a threshold voltage of the storage capacitor.

The storage capacitor can be formed by utilizing a formation process of the transistor. A light-transmitting semiconductor film functioning as one electrode of the storage capacitor can be formed by utilizing a formation process of a semiconductor film included in the transistor. That is, the light-transmitting semiconductor film functioning as one electrode of the storage capacitor is formed on the same surface as the light-transmitting semiconductor film of the transistor. An oxide semiconductor film can be used as the light-transmitting semiconductor film of the transistor, and a transistor using an oxide semiconductor film formed by performing appropriate treatment is an enhancement type transistor. Since the off-state current of the transistor is extremely low, the power consumption of the semiconductor device can be reduced.

Note that in the following description, a semiconductor film included in a transistor and a light-transmitting semiconductor film included in a storage capacitor are described as an oxide semiconductor film.

In the above, the oxide semiconductor film included in the storage capacitor and the oxide semiconductor film included in the transistor have the same carrier density.
The oxide semiconductor film is not subjected to treatment for adding impurities which increase electrical conductivity in order to intentionally increase the carrier density.

In a semiconductor device according to one embodiment of the present invention, a transistor functioning as a switching element is an enhancement-type transistor having an oxide semiconductor film, and an oxide semiconductor film formed simultaneously with the oxide semiconductor film constituting the enhancement-type transistor is used for one electrode of a storage capacitor. In this way, the voltage range for driving the semiconductor device can be narrowed compared to a semiconductor device using a depletion-type transistor, and the power consumption of the semiconductor device can be reduced.

In addition, the dielectric film of the storage capacitor can be an insulating film provided over an oxide semiconductor film included in a transistor, and the light-transmitting conductive film functioning as the other electrode of the storage capacitor can be a pixel electrode included in a display element and electrically connected to the transistor.

In this manner, since the storage capacitor has light-transmitting properties, it can be formed large (with a large area) in a region of the pixel other than the region where the transistor is formed. Therefore, according to one embodiment of the present invention, a semiconductor device with an increased aperture ratio and an increased charge capacitance can be obtained. Furthermore, by improving the aperture ratio, a semiconductor device with excellent display quality can be obtained.

Note that one embodiment of the present invention includes not only the semiconductor device but also a method for driving the semiconductor device.

One embodiment of the present invention is a method for driving a display device including a pixel having an enhancement type transistor, a pixel electrode to which a predetermined potential is supplied from a signal line via the transistor, and a storage capacitor having a light-transmitting semiconductor film that functions as one electrode of the pixel electrode and is electrically connected to a capacitance line and functions as the other electrode, the method comprising the steps of: supplying a potential that is equal to or higher than a threshold voltage of the transistor to a scan line having a gate electrode of the transistor to turn the transistor on; supplying a predetermined potential from the signal line to the pixel electrode; and supplying a potential to the capacitance line such that a potential difference between the light-transmitting semiconductor film and the capacitance line is higher than a threshold voltage of the storage capacitor, thereby causing the storage capacitor to store a potential difference between the potential of the pixel electrode and the potential of the capacitance line for a certain period.

Another embodiment of the present invention is a pixel electrode including an enhancement type transistor, a pixel electrode to which a predetermined potential is supplied from a signal line through the transistor, and a pixel electrode which functions as one of the electrodes.
A method for driving a display device including a pixel having a storage capacitor including a light-transmitting semiconductor film electrically connected to a storage capacitor line and functioning as the other electrode, the method comprising: supplying a potential equal to or higher than a threshold voltage of the transistor to a scan line having a gate electrode of the transistor to turn the transistor on; supplying a predetermined potential from a signal line to the pixel electrode; and supplying a potential to the storage capacitor line that is lower than the predetermined potential supplied to the pixel electrode by at least the threshold voltage of the storage capacitor, thereby causing the storage capacitor to store a potential difference between the potential of the pixel electrode and the potential of the storage capacitor line for a certain period of time.

By using the above driving method, the operating range of a storage capacitor of a semiconductor device including a storage capacitor having a light-transmitting semiconductor film, a light-transmitting conductive film, and a light-transmitting insulating film can be expanded, and the storage capacitor can be operated stably.

In this specification, the threshold voltage of a storage capacitance refers to a voltage at which an accumulation layer is formed in a light-transmitting semiconductor film and the charge capacitance begins to increase, when a so-called MOS capacitance is considered to be formed by a light-transmitting semiconductor film, a pixel electrode, and an insulating film provided between the pixel electrode and the insulating film.

In a semiconductor device including a storage capacitor having a light-transmitting semiconductor film, a light-transmitting conductive film, and a light-transmitting insulating film, a method for stably operating the storage capacitor can be provided. In addition, according to one embodiment of the present invention, a semiconductor device having a high aperture ratio, a storage capacitor with a large charge capacitance, and reduced power consumption can be provided.

1A and 1B are a diagram showing a semiconductor device and a circuit diagram of a pixel. 11A and 11B are graphs showing Id-Vg curves of a transistor included in a semiconductor device, CV curves of a storage capacitor, and potentials of a pixel electrode and a capacitor line. 1A to 1C are diagrams illustrating a method of operating a storage capacitor included in a semiconductor device. FIG. 2 is a top view showing a pixel of a semiconductor device. FIG. 1 is a cross-sectional view showing a pixel of a semiconductor device. 1A to 1C are cross-sectional views illustrating a method for manufacturing a pixel of a semiconductor device. 1A to 1C are cross-sectional views illustrating a method for manufacturing a pixel of a semiconductor device. FIG. 2 is a top view showing a pixel of a semiconductor device. FIG. 1 is a cross-sectional view showing a pixel of a semiconductor device. FIG. 1 is a cross-sectional view showing a pixel of a semiconductor device. FIG. 2 is a top view showing a pixel of a semiconductor device. FIG. 1 is a cross-sectional view showing a pixel of a semiconductor device. FIG. 2 is a top view showing a pixel of a semiconductor device. FIG. 1 is a cross-sectional view showing a pixel of a semiconductor device. FIG. 2 is a top view showing a pixel of a semiconductor device. FIG. 2 is a top view showing a pixel of a semiconductor device. 1 is a cross-sectional view illustrating a transistor that can be used in a pixel of a semiconductor device. FIG. 1 is a top view showing a semiconductor device. FIG. 1 is a cross-sectional view showing a semiconductor device. FIG. 1 is a cross-sectional view showing a semiconductor device. 1A and 1B are a top view and a cross-sectional view showing a part of a scanning line driver circuit of a semiconductor device. 1A and 1B are a top view and a cross-sectional view showing a common connection portion of a semiconductor device. 1A to 1C are diagrams illustrating electronic devices using semiconductor devices. 1A to 1C are diagrams illustrating electronic devices using semiconductor devices.

Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that the form and details of the present invention can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the description of the embodiments shown below.

In the configuration of the present invention described below, the same parts or parts having similar functions are denoted by the same reference numerals in different drawings, and the repeated explanations are omitted. In addition, when referring to parts having similar functions, the same hatch pattern may be used and no particular reference numeral may be used.

In each figure described in this specification, the size of each component, the thickness of a film, or an area may be exaggerated for clarity, and therefore are not necessarily limited to the scale.

In this specification and the like, ordinal numbers such as first, second, etc. are used for convenience and do not indicate the order of steps or stacking. Furthermore, in this specification and the like, they do not indicate specific names as matters for identifying the invention.

In addition, the functions of the "source" and "drain" in the present invention may be interchanged when the direction of the current changes during the circuit operation.
The terms "source" and "drain" may be used interchangeably.

Furthermore, voltage refers to the potential difference between two points, and potential refers to the electrostatic energy (electrical potential energy) of a unit charge in an electrostatic field at a certain point. However, in general, the potential difference between the potential at a certain point and a reference potential (e.g., ground potential) is simply called potential or voltage, and potential and voltage are often used as synonyms. For this reason, in this specification, unless otherwise specified, potential may be read as voltage, and voltage may be read as potential.

In this specification, when etching is performed after photolithography, the mask formed in the photolithography is removed.

(Embodiment 1)
In this embodiment, a semiconductor device according to one embodiment of the present invention and a method for driving the semiconductor device will be described with reference to the drawings. Note that in this embodiment, the semiconductor device according to one embodiment of the present invention will be described as a liquid crystal display device.

(Configuration of Semiconductor Device)
FIG. 1A illustrates a configuration example of a semiconductor device. The semiconductor device illustrated in FIG.
The pixel section 100, the scanning line driving circuit 104, the signal line driving circuit 106, and m scanning lines 104 are arranged in parallel or approximately in parallel, and the potentials of the scanning line driving circuit 104 are controlled by the scanning line driving circuit 104.
The pixel portion 100 has n scanning lines 107 and n signal lines 109 arranged in parallel or approximately parallel to each other and whose potentials are controlled by a signal line driver circuit 106. The pixel portion 100 further has a plurality of pixels 101 arranged in a matrix. The pixel portion 100 also has capacitance lines 115 arranged in parallel or approximately parallel to each other along the scanning lines 107. Note that the capacitance lines 115 may be arranged in parallel or approximately parallel to each other along the signal lines 109.

Each scanning line 107 is electrically connected to n pixels 101 arranged in any one of the rows of the pixels 101 arranged in m rows and n columns in the pixel section 100.
is m pixels 101 arranged in m rows and n columns, which are arranged in any one of the columns.
1. Both m and n are integers of 1 or more.
is n pixels 101 arranged in any one of the rows among the pixels 101 arranged in m rows and n columns.
When the capacitance lines 115 are arranged parallel or approximately parallel to each other along the signal line 109, the capacitance lines 115 are electrically connected to m pixels 101 arranged in any one of the columns of the pixels 101 arranged in m rows and n columns.

1B is an example of a circuit diagram of a pixel 101 included in the semiconductor device shown in FIG 1A. The pixel 101 shown in FIG 1B includes a transistor 103 electrically connected to a scan line 107 and a signal line 109, and a storage capacitor 111 having one electrode electrically connected to a capacitor line 115 that supplies a constant potential and the other electrode electrically connected to a drain electrode of the transistor 103.
05, and a liquid crystal element 108 in which a pixel electrode 121 is electrically connected to the drain electrode of the transistor 103 and the other electrode of the storage capacitor 105, and an electrode (opposite electrode) provided opposite the pixel electrode 121 is electrically connected to a wiring that supplies an opposite potential.

The transistor 103 is an enhancement type transistor. Therefore, when the threshold voltage is 0 V or higher, that is, when the gate voltage (Vg) is 0 V or higher, an on-current (drain current: Id) flows and the transistor 103 is turned on (see FIG. 2A).
In other words, when no gate voltage is applied, no on-current flows.
In this specification, the gate voltage refers to a potential difference between a gate electrode and a source electrode.

When an oxide semiconductor film that is treated under appropriate conditions is used for a channel formation region of a transistor, the off-state current of the transistor can be significantly reduced.
Since the oxide semiconductor film 111 that is treated under appropriate conditions is used for a channel formation region of the transistor 103, the off-state current of the transistor 103 is extremely low. Thus, the semiconductor device of one embodiment of the present invention has low power consumption.

A transistor using an oxide semiconductor with increased carrier density is a depletion-type transistor. On the other hand, the transistor 103 is an enhancement-type transistor, and the oxide semiconductor film 111 included in the transistor 103 is an oxide semiconductor film to which no treatment of adding an impurity for increasing electrical conductivity has been performed in order to intentionally increase the carrier density.

The storage capacitor 105 has a dielectric film provided between a pair of electrodes and has light-transmitting properties. One electrode of the storage capacitor 105 is an oxide semiconductor film 119, the dielectric film is a light-transmitting insulating film provided on an oxide semiconductor film 111 included in the transistor 103, and the other electrode is a pixel electrode 121.
The storage capacitor 105 can be formed by utilizing the formation process of the pixel electrode 121. The oxide semiconductor film 119 functions as one of the electrodes by controlling a potential applied to the pixel electrode 121 and bringing the oxide semiconductor film 119 into a conductive state.
It can be said that this is a (conductor) capacitor structure.

In addition, since the oxide semiconductor film 119 of the storage capacitor 105 is formed by utilizing the formation process of the oxide semiconductor film 111 included in the transistor 103, which is an enhancement type transistor, the storage capacitor 105 starts to charge when the potential difference between the pixel electrode 121 and the capacitance line 115 becomes 0 V or higher, similarly to the transistor 103. In other words, the threshold voltage of the storage capacitor 105 is 0 V or higher.

2B shows a CV curve of the storage capacitor 105. In FIG. 2B, the horizontal axis represents the potential difference (VP-VC) between the pixel electrode 121 and the capacitance line 115 of the storage capacitor 105, and the vertical axis represents the capacitance (C) relative to the potential difference.
When the frequency of the voltage during the time-domain measurement is lower than the frame frequency of the semiconductor device, a CV curve as shown in FIG.

In this specification, the potential difference between the pixel electrode 121 and the capacitance line 115 is
The potential (V) of the capacitance line 115 is subtracted from the potential (V) of the capacitance line 115 (see FIG. 2C).
Note that in FIG. 2C, the transistor 103 and the storage capacitor 105 are shown for clarity.

The oxide semiconductor film 119 of the storage capacitor 105 can be formed by utilizing the formation process of the oxide semiconductor film 111 included in the transistor 103, and therefore is an oxide semiconductor film to which no treatment of adding impurities that increase electrical conductivity has been performed in order to intentionally increase the carrier density. The carrier density of the oxide semiconductor film 119 is equivalent to that of the oxide semiconductor film 111.

As described above, since the oxide semiconductor film 119 of the storage capacitor 105 and the oxide semiconductor film 111 included in the transistor 103 have the same structure, the threshold voltage (Vth) of the storage capacitor 105
is equal to the threshold voltage (Vth_Tr) of the transistor 103 (see FIGS. 2A and 2B).

The liquid crystal element 108 is an element that controls the transmission or non-transmission of light by the optical modulation action of liquid crystal sandwiched between a substrate on which the transistor 103 and pixel electrode 121 are formed and a substrate on which a counter electrode is formed. Note that the optical modulation action of the liquid crystal is controlled by an electric field (including a vertical electric field or an oblique electric field) applied to the liquid crystal. Note that when a counter electrode (also called a common electrode) is formed on the substrate on which the pixel electrode is formed, the electric field applied to the liquid crystal becomes a horizontal electric field.

The scanning line driver circuit 104 and the signal line driver circuit 106 are roughly divided into a logic circuit portion and a switch portion or a buffer portion. Although detailed configurations of the scanning line driver circuit 104 and the signal line driver circuit 106 are omitted, the scanning line driver circuit 104 and the signal line driver circuit 106 include transistors.

Note that the transistors included in one or both of the scanning line driver circuit 104 and the signal line driver circuit 106 can be formed by utilizing the formation process of the transistor 103.
One or both of the scanning line driver circuit 104 and the signal line driver circuit 106 can be provided on the substrate on which the transistor 103 and the pixel electrode 121 are provided. By integrally forming one or both of the scanning line driver circuit 104 and the signal line driver circuit 106 on the substrate in this manner, the number of components of the semiconductor device can be reduced, and the manufacturing cost can be reduced.

In addition, the transistors included in one or both of the scanning line driver circuit 104 and the signal line driver circuit 106 are preferably enhancement type transistors rather than depletion type transistors in order to properly operate the scanning line driver circuit 104 and the signal line driver circuit 106. For this reason, it is significant to use an enhancement type transistor for the transistor 103.

As described above, since the storage capacitor 105 has light-transmitting properties, it can be formed large (with a large area) in a region other than the region where the transistor 103 of the pixel 101 is formed. Therefore, the semiconductor device illustrated in FIG. 1 is a semiconductor device in which the aperture ratio is increased and the charge capacitance is increased. In addition, the semiconductor device has excellent display quality. For example, in the semiconductor device according to one embodiment of the present invention,
In the case where the pixel aperture ratio is set to about 100 ppi to 330 ppi, the pixel aperture ratio can be set to 50% or more, further to 55% or more, and further to 60% or more. Another embodiment of the present invention is a semiconductor device having a pixel aperture ratio higher than that of a conventional semiconductor device.

Here, a method for driving the semiconductor device according to one embodiment of the present invention will be described. Since the semiconductor device according to one embodiment of the present invention has a storage capacitor 105 having a MOS capacitor structure,
In order to stably operate the storage capacitor 105, a potential applied to the oxide semiconductor film 119 (in other words, the capacitor line 115) functioning as one electrode of the storage capacitor 105 is set as follows.

The CV curve of the storage capacitor 105 is a CV curve with a threshold voltage of 0 V or more, as shown in FIG. 2B. In order to stably operate the storage capacitor 105 during the period in which the storage capacitor 105 is operated, the storage capacitor 105 is kept in a sufficiently charged state. For example, the potential difference (VP
A potential VC is applied to the capacitance line 115 so that the potential VC −VC is equal to or higher than V1 and equal to or lower than V2 in FIG. 2B (see FIGS. 2B and 2C).

During the period in which the storage capacitor 105 is operated, the potential of the pixel electrode 121 is
09. Specifically, it fluctuates in the positive and negative directions based on the central potential of the video signal. Therefore, in order to set the potential difference (VP-VC) to be V1 or more and V2 or less during that period, the potential (VC) of the capacitance line 115 (oxide semiconductor film 119) may be set to a potential lower than the low potential of the pixel electrode 121 by at least the threshold voltage of the storage capacitor 105 (see FIG. 3). Note that in FIG. 3, the lowest potential of the potentials supplied to the scanning line 107 is designated as GVss, and the highest potential is designated as GVdd.

In other words, in order to operate the storage capacitor 105, it is only necessary that the potential difference between the pixel electrode 121 and the capacitance line 115 (oxide semiconductor film 119) is higher than the threshold voltage of the storage capacitor 105 during the period in which the storage capacitor 105 is operated.

Further, since the threshold voltage of the storage capacitor 105 is equal to the threshold voltage of the transistor 103, the potential of the capacitor line 115 (the oxide semiconductor film 119) may be set lower by equal to or more than the threshold voltage of the transistor 103. In this manner, the oxide semiconductor film 119 can be always kept in a conductive state during a period in which the storage capacitor 105 is operated, and the storage capacitor 105 can be operated stably.

As described above, by using the driving method of one embodiment of the present invention,
In a semiconductor device including a storage capacitor having a light-transmitting conductive film and a light-transmitting insulating film, the storage capacitor can be operated stably over time.

The transistor 103 is an enhancement type transistor, and the storage capacitor 10
5 is formed by utilizing the formation process of the transistor 103, which is an enhancement type transistor. Therefore, the voltage range required to drive the storage capacitor in the semiconductor device of one embodiment of the present invention is narrower than the voltage range required to drive a storage capacitor formed using an oxide semiconductor film with increased carrier density, which is formed by using a depletion type transistor as the transistor and utilizing the formation process of the depletion type transistor.
Therefore, according to one embodiment of the present invention, the power consumption of a semiconductor device can be reduced.

<Top and cross-sectional structures of semiconductor device>
Next, a specific structure of the semiconductor device will be described. Here, the pixel 101 will be described as an example. A top view of the pixel 101 is shown in Fig. 4. Note that in Fig. 4, some of the components of the semiconductor device (such as a liquid crystal element 108) are omitted for clarity.

4, the scanning lines 107 are provided so as to extend in a direction (horizontal direction in the drawing) substantially perpendicular to the signal lines 109. The signal lines 109 are provided so as to extend in a direction (vertical direction in the drawing) substantially perpendicular to the scanning lines 107. The capacitance lines 115 are provided so as to extend in a direction parallel to the scanning lines 107. The scanning lines 107 and the capacitance lines 115 are connected to the scanning line driving circuit 104 (FIG. 1(A)).
1( )) and the signal line 109 is electrically connected to a signal line driver circuit 106 (see FIG. 1(
A) is electrically connected to the

The transistor 103 is provided in a region where the scan line 107 and the signal line 109 intersect. The transistor 103 includes at least an oxide semiconductor film 11 having a channel formation region.
1, a gate electrode, a gate insulating film (not shown in FIG. 4), a source electrode, and a drain electrode.

The scanning line 107 includes a region that functions as a gate electrode of the transistor 103, and the signal line 109 includes a region that functions as a source electrode of the transistor 103.
includes a region that functions as a drain electrode of the transistor 103, and is electrically connected to a pixel electrode 121 through an opening 117. Note that in FIG. 4, the pixel electrode 121 is illustrated without hatching.

The region functioning as a gate electrode is formed by forming the oxide semiconductor film 1
11. The region functioning as a source electrode is a region of the signal line 109 that overlaps with at least the oxide semiconductor film 111. The region functioning as a drain electrode is a region of the conductive film 113 that overlaps with at least the oxide semiconductor film 111. Note that hereinafter, the gate electrode of the transistor 103 may be referred to as the scan line 107, and the source electrode of the transistor 103 may be referred to as the signal line 109. The drain electrode of the transistor 103 may be referred to as the conductive film 11
It is written as 3.

Further, the end of the scanning line 107 is located outside the end of the semiconductor film in the top view.
For this reason, the scan line 107 functions as a light-shielding film that blocks light from a light source such as a backlight. As a result, the oxide semiconductor film 111 included in the transistor is not irradiated with light, and fluctuations in the electrical characteristics of the transistor can be suppressed.

The storage capacitor 105 is provided in a region surrounded by the scanning line 107 and the signal line 109. The storage capacitor 105 is composed of an oxide semiconductor film 119, a light-transmitting pixel electrode 121, and a light-transmitting insulating film (not shown in FIG. 4 ) formed on the transistor 103 as a dielectric film. The oxide semiconductor film 119, the light-transmitting pixel electrode 121, and the dielectric film each have light-transmitting properties, and therefore the storage capacitor 105 has light-transmitting properties.
The oxide semiconductor film 119 is in contact with the capacitor line 115 through the conductive film 125 provided in the opening 123 , and thus the storage capacitor 105 is electrically connected to the capacitor line 115 .

The amount of charge stored in the storage capacitor changes depending on the area where the pair of electrodes overlap.
When the size of a pixel is reduced to increase the resolution, the size of the storage capacitor is also reduced accordingly, and the charge capacity that can be stored is reduced. As a result, there is a possibility that the liquid crystal element cannot be operated sufficiently. Since the storage capacitor 105 has light-transmitting properties, it is possible to form the storage capacitor as large as possible (large area) within the pixel, and the storage capacitor can be formed over the entire range in which the liquid crystal element 108 operates. As long as a charge capacity that can operate the liquid crystal element sufficiently can be secured, the pixel density can be increased and the resolution can be increased.

Here, the characteristics of a transistor using an oxide semiconductor are described. A transistor using an oxide semiconductor is an n-channel transistor. Oxygen vacancies contained in the oxide semiconductor may cause carriers to be generated, which may degrade the electrical characteristics and reliability of the transistor. For example, the threshold voltage of the transistor may shift in the negative direction, and a drain current may flow when the gate voltage is 0 V. Such a state in which a drain current flows when the gate voltage is 0 V is called a normally-on characteristic.
A transistor in which it can be considered that no drain current flows when the gate voltage is 0 V is called a normally-off transistor.

Therefore, when an oxide semiconductor film is used, it is preferable that defects contained in the oxide semiconductor film, typically oxygen vacancies, are reduced as much as possible. For example, it is preferable that the spin density (corresponding to the defect density contained in the oxide semiconductor film) with a g value of 1.93 measured by electron spin resonance in which a magnetic field is applied parallel to the film surface is reduced to a lower limit of detection by a measuring device or less. By reducing defects contained in the oxide semiconductor film, typically oxygen vacancies, as much as possible, a transistor can be prevented from becoming normally on, and the electrical characteristics and reliability of a semiconductor device can be improved.

A shift in the threshold voltage of a transistor in the negative direction can be caused not only by oxygen vacancies but also by hydrogen (including hydrogen compounds such as water) contained in the oxide semiconductor film. Hydrogen contained in the oxide semiconductor film reacts with oxygen that is bonded to metal atoms to form water, and a vacancy (which can also be referred to as oxygen vacancy) occurs in the lattice from which oxygen has been released (or in the portion from which oxygen has been released).
In addition, part of the hydrogen reacts with oxygen to generate electrons that serve as carriers. Therefore, a transistor including an oxide semiconductor film containing hydrogen tends to have normally-on characteristics.

From the above, it is preferable that hydrogen be reduced as much as possible in the oxide semiconductor film 111 included in the transistor 103. Specifically, the oxide semiconductor film 111 is analyzed by secondary ion mass spectrometry (SIMS).
The hydrogen concentration obtained by the hydrogen concentration measuring method is less than 5×10 ¹⁸ atoms/cm ³ , preferably 1×10 ¹⁸ atoms/cm ³ or less, more preferably 5×10 ¹⁷ atoms/cm 3 or less.
^m3 or less, and more preferably 1×10 ¹⁶ atoms/cm ³ or less.

The oxide semiconductor film 111 has an alkali metal or alkaline earth metal concentration measured by secondary ion mass spectrometry of 1×10 ¹⁸ atoms/cm or less, preferably 2×10 18 atoms/cm ^or less.
The concentration is set to 0 ^{to 16} atoms/cm ³ or less. When an alkali metal or an alkaline earth metal is bonded to an oxide semiconductor, carriers might be generated, which might increase the off-state current of the transistor 103 .

Furthermore, when the oxide semiconductor film 111 contains nitrogen, electrons that serve as carriers are generated, the carrier density increases, and the oxide semiconductor film 111 tends to become an n-type transistor. As a result, a transistor including the oxide semiconductor film containing nitrogen tends to have normally-on characteristics.
In the above, it is preferable that the nitrogen is reduced as much as possible. For example, the nitrogen concentration is 5×
It is preferable to set the concentration to 10 ¹⁸ atoms/cm ³ or less.

In addition, when an oxide semiconductor contains a Group 14 element such as silicon or carbon, electrons serving as carriers are generated, the carrier density increases, and the oxide semiconductor is easily made n-type. Therefore, in a transistor having an oxide semiconductor film, particularly at the interface between the gate insulating film 127 (not shown in FIG. 4 ) and the oxide semiconductor film 111, the silicon concentration obtained by secondary ion mass spectrometry is 3×10 ¹⁸ atoms/cm ³ or less, preferably 3×10 ¹⁷ atoms/cm ^3.
At the interface, the carbon concentration obtained by secondary ion mass spectrometry is 3×10 ¹⁸ atoms/cm ³ or less, and preferably 3×10 ¹⁷ atoms/cm ³ or less.

As described above, by using the highly purified oxide semiconductor film 111 in which impurities (such as hydrogen, nitrogen, silicon, carbon, an alkali metal, or an alkaline earth metal) are reduced as much as possible, the transistor 103 can be prevented from having normally-on characteristics, and the off-state current of the transistor 103 can be significantly reduced. Thus, one embodiment of the present invention is a semiconductor device having favorable electrical characteristics and excellent reliability. Note that a highly purified oxide semiconductor can be said to be an intrinsic or substantially intrinsic semiconductor.

The transistor 103 is an enhancement type transistor, and the oxide semiconductor film 111 is an oxide semiconductor film to which no treatment of adding an impurity for increasing electrical conductivity or the like has been performed in order to intentionally increase the carrier density. Therefore, the carrier density of the oxide semiconductor film 111 is 1×10 ¹⁷ /cm ³ or less, or 1×10 ¹⁶ /cm ³ or less, or 1×10 ¹⁵ /cm ³ or less, or 1×10 ¹⁴ /cm ³ or less, or 1×10 ¹³ /cm
³ or less.

In addition, the oxide semiconductor film 119 included in the storage capacitor 105 can be formed by utilizing the formation process of the oxide semiconductor film 111 included in the transistor 103.
The carrier density of the oxide semiconductor film 119 is equal to that of the oxide semiconductor film 111, and therefore the carrier density of the oxide semiconductor film 119 is in the above range.

The reason why the off-state current of a transistor using a highly purified oxide semiconductor film is low is that
This can be proved by various experiments. For example, if the channel width is 1×10 ⁶ μm and the channel length is L
Even if the element has a thickness of 10 μm, the voltage between the source electrode and the drain electrode (drain voltage) is 1
In the range of V to 10 V, the off-current is equal to or less than the measurement limit of the semiconductor parameter analyzer, that is, 1×10 ⁻¹³ A or less. In this case, it is found that the off-current equivalent to the value divided by the channel width of the transistor is equal to or less than 100 zA/μm. In addition, the off-current was measured using a circuit in which a storage capacitor and a transistor are connected and the transistor controls the charge flowing into or out of the storage capacitor. In this measurement, a highly purified oxide semiconductor film was used in the channel formation region of the transistor, and the off-current of the transistor was measured from the change in the amount of charge per unit time of the storage capacitor. As a result, it was found that an even lower off-current of several tens of yA/μm was obtained when the voltage between the source electrode and the drain electrode of the transistor was 3 V. Therefore, the transistor using the highly purified oxide semiconductor film has a significantly small off-current.

Next, cross-sectional views taken along dashed lines A1-A2 and B1-B2 in FIG. 4 are shown in FIG.

The cross-sectional structures between dashed dotted lines A1-A2 and B1-B2 are as follows. A scanning line 107 including a region functioning as a gate electrode and a capacitance line 115 are provided over a substrate 102. A gate insulating film 127 is provided over the scanning line 107 and the capacitance line 115. An oxide semiconductor film 111 is provided over a region of the gate insulating film 127 overlapping with the scanning line 107. An oxide semiconductor film 119 is provided over the gate insulating film 127. A signal line 109 including a region functioning as a source electrode and a conductive film 113 including a region functioning as a drain electrode are provided over the oxide semiconductor film 111 and the gate insulating film 127. An opening 1 reaching the capacitance line 115 is provided in a part of the gate insulating film 127 in contact with the capacitance line 115.
23, and a conductive film 125 is provided over the opening 123, the gate insulating film 127, and the oxide semiconductor film 119. An insulating film 129, an insulating film 131, and an insulating film 132 which function as protective insulating films for the transistor 103 are provided over the gate insulating film 127, the signal line 109, the oxide semiconductor film 111, the conductive film 113, the conductive film 125, and the oxide semiconductor film 119.
An opening 117 reaching the conductive film 113 is provided in the insulating films 129, 131, and 132, and the pixel electrode 121 is provided on the opening 117 and the insulating film 132.
An alignment film 158 is provided on the pixel electrodes 121 and the insulating film 132. Note that a base insulating film may be provided between the substrate 102, the scanning lines 107, the capacitance lines 115, and the gate insulating film 127.

The cross-sectional structure of the liquid crystal element 108 is as follows. A light-shielding film 152 is provided on at least a region of the surface of the substrate 150 facing the substrate 102 that overlaps with the transistor 103, a counter electrode 154 that is a conductive film having light-transmitting properties is provided so as to cover the light-shielding film 152, and an alignment film 156 is provided so as to cover the counter electrode. An alignment film 158 is provided on the pixel electrode 121 and the insulating film 132. The alignment film 158 is provided on the insulating film 132 on the substrate 102 side and the pixel electrode 121. The liquid crystal 160 is formed by the alignment film 156 and the alignment film 158.
1 and is sandwiched between the substrate 102 and the substrate 150 .

In the case where the semiconductor device of one embodiment of the present invention is used as a liquid crystal display device, a light source such as a backlight, optical members (optical substrates) such as polarizing plates provided on the substrate 102 side and the substrate 150 side, a sealant for fixing the substrate 102 and the substrate 150, and the like are required; these will be described later.

As described above, in the storage capacitor 105 described in this embodiment, one of a pair of electrodes is the oxide semiconductor film 119, and the other of the pair of electrodes is the pixel electrode 121.
The dielectric films provided between the pair of electrodes are the insulating films 129, 131, and 132.
It is.

The components of the above cross-sectional structure are described in detail below.

There is no particular limitation on the material of the substrate 102, but the substrate 102 must have at least heat resistance sufficient to withstand heat treatment performed in a manufacturing process of a semiconductor device. For example, a glass substrate, a ceramic substrate, a plastic substrate, or the like may be used. As the glass substrate, an alkali-free glass substrate such as barium borosilicate glass, aluminoborosilicate glass, or aluminosilicate glass may be used. A substrate that does not have light-transmitting properties, such as a stainless steel alloy, may also be used. In that case, it is preferable to provide an insulating film on the substrate surface. Note that a quartz substrate, a sapphire substrate, a single crystal semiconductor substrate, a polycrystalline semiconductor substrate, a compound semiconductor substrate, an SOI (Silicon On Insulator) substrate, or the like may also be used as the substrate 102. Note that when the semiconductor device according to one embodiment of the present invention is used as a transmissive liquid crystal display device, the substrate 102 is a substrate having light-transmitting properties.

The scanning line 107 and the capacitance line 115 are preferably formed of a metal film in order to pass a large current therethrough. Representative examples of the metal film include molybdenum (Mo), titanium (Ti), tungsten (W), and tantalum (
The insulating layer 11 is provided in a single layer structure or a multilayer structure using a metal material such as Ta, aluminum (Al), copper (Cu), chromium (Cr), neodymium (Nd), scandium (Sc), or an alloy material having these as main components.

Examples of the scanning line 107 and the capacitance line 115 include a single-layer structure using aluminum containing silicon, a two-layer structure in which titanium is laminated on aluminum, a two-layer structure in which titanium is laminated on titanium nitride, a two-layer structure in which tungsten is laminated on titanium nitride, a two-layer structure in which tungsten is laminated on tantalum nitride, a two-layer structure in which copper is laminated on a copper-magnesium-aluminum alloy, and a three-layer structure in which copper is laminated on titanium nitride and tungsten is further formed on top of that.

Further, a conductive material having a light-transmitting property that can be applied to the pixel electrode 121 can be used as a material for the scan line 107 and the capacitor line 115. Note that when the semiconductor device which is one embodiment of the present invention is used as a reflective display device, a conductive material that does not transmit light (for example, a metal material) can be used for the pixel electrode 121. In that case, a substrate that does not transmit light can also be used for the substrate 102.

Furthermore, as the material of the scan line 107 and the capacitance line 115, a metal oxide containing nitrogen, specifically, an In-Ga-Zn-based oxide containing nitrogen, an In-Sn-based oxide containing nitrogen, an In-Ga-based oxide containing nitrogen, an In-Zn-based oxide containing nitrogen, a Sn-based oxide containing nitrogen, an In-based oxide containing nitrogen, or a metal nitride film (InN, SnN, etc.) can be used. These materials have a work function of 5 eV (electron volts) or more. By using these metal oxides containing nitrogen as the scan line (gate electrode), the threshold voltage of the transistor 103 can be shifted in the positive direction, and a transistor having so-called normally-off characteristics can be realized. For example, when an In-Ga-Zn-based oxide containing nitrogen is used, a nitrogen concentration higher than that of the oxide semiconductor film 111, specifically, a nitrogen concentration of 7 atomic % or more, is preferably 7 atomic % or more.
An n-Ga-Zn oxide can be used.

It is preferable to use aluminum or copper, which is a low resistance material, in the scanning line 107 and the capacitance line 115. By using aluminum or copper, it is possible to reduce signal delay and improve display quality. Aluminum has low heat resistance and is prone to defects due to hillocks, whiskers, or migration. In order to prevent the migration of aluminum, it is preferable to laminate a metal material having a higher melting point than aluminum, such as molybdenum, titanium, or tungsten, on the aluminum. Also, when copper is used, it is preferable to laminate a metal material having a higher melting point than copper, such as molybdenum, titanium, or tungsten, in order to prevent defects due to migration and diffusion of copper elements.

4 and 5, the scan line 107 is preferably provided in a shape that allows the oxide semiconductor film 111 to be provided in a region of the scan line 107.
It is preferable that the scanning lines 107 be provided on the inner side of the scanning lines 107. In this way, light (light from a light source such as a backlight in a liquid crystal display device) irradiated from the surface (the back surface of the substrate 102) opposite to the surface on which the scanning lines 107 are provided of the substrate 102 is reflected by the scanning lines 107.
Since the insulating film 07 blocks light, fluctuation or deterioration of the electrical characteristics (eg, threshold voltage) of the transistor 103 can be suppressed.

The gate insulating film 127 is made of, for example, silicon oxide, silicon oxynitride, silicon nitride oxide,
The gate insulating film 127 has a single-layer structure or a stacked-layer structure using an insulating material such as silicon nitride, aluminum oxide, hafnium oxide, gallium oxide, or a Ga-Zn-based metal oxide. Note that in order to improve interface characteristics with the oxide semiconductor film 111, at least a region of the gate insulating film 127 in contact with the oxide semiconductor film 111 is preferably formed using an oxide insulating film.

Furthermore, by providing the gate insulating film 127 with an insulating film having a barrier property against oxygen, hydrogen, water, and the like, it is possible to prevent oxygen contained in the oxide semiconductor film 111 from diffusing to the outside and to prevent hydrogen, water, and the like from entering the oxide semiconductor film 111 from the outside. Examples of insulating films having a barrier property against oxygen, hydrogen, water, and the like include an aluminum oxide film, an aluminum oxynitride film, a gallium oxide film, a gallium oxynitride film, an yttrium oxide film, an yttrium oxynitride film, a hafnium oxide film, a hafnium oxynitride film, and a silicon nitride film.

In addition, by using a high-k material such as hafnium silicate (HfSiO _x ), hafnium silicate containing nitrogen (HfSi _x O _y N _z ), hafnium aluminate containing nitrogen (HfAl _x O _y N _z ), hafnium oxide, or yttrium oxide for the gate insulating film 127, the gate leakage current of the transistor 103 can be reduced.

The gate insulating film 127 preferably has the following stacked structure: a silicon nitride film with a small amount of defects is provided as a first silicon nitride film, a silicon nitride film with a small amount of hydrogen desorption and ammonia desorption is provided as a second silicon nitride film on the first silicon nitride film, and any of the oxide insulating films applicable to the gate insulating film 127 is provided on the second silicon nitride film.

The second silicon nitride film is a film in which the amount of desorption of hydrogen molecules is 5
x ¹⁰²¹ molecules/cm3 or ^less , preferably 3 x ¹⁰²¹ molecules/cm3 or ^less , more preferably 1 x ¹⁰²¹ molecules/ ^cm3 or less, and the amount of ammonia molecules desorbed is less than 1 x ¹⁰²² molecules/ ^cm3 , preferably 5 x ¹⁰²¹ molecules/ ^cm3 or less, more preferably 1 x ¹⁰²² molecules/cm3 or less.
It is preferable to use a nitride insulating film having a conductivity of ¹ molecule/cm ³ or less. By using the first silicon nitride film and the second silicon nitride film as part of the gate insulating film 127, a gate insulating film with fewer defects and with smaller amounts of desorption of hydrogen and ammonia can be formed as the gate insulating film 127. As a result, the amounts of hydrogen and nitrogen contained in the gate insulating film 127 that move to the oxide semiconductor film 111 can be reduced.

In a transistor including an oxide semiconductor, the presence of a trap state (also referred to as an interface state) at the interface between the oxide semiconductor film and the gate insulating film or at the gate insulating film causes a shift in the threshold voltage of the transistor, typically in the negative direction, and an increase in a subthreshold coefficient (S value) indicating a gate voltage required for a drain current to change by one order of magnitude when the transistor is turned on. As a result, there is a problem that the electrical characteristics vary from transistor to transistor. For this reason, by using a silicon nitride film with few defects as the gate insulating film and by providing an oxide insulating film in a region in contact with the oxide semiconductor film 111, a negative shift in the threshold voltage can be reduced and an increase in the S value can be suppressed.

The thickness of the gate insulating film 127 is 5 nm to 400 nm, preferably 10 nm to 300 nm.
00 nm or less, and more preferably 50 nm or more and 250 nm or less.

The oxide semiconductor film 111 and the oxide semiconductor film 119 can have an amorphous structure, a single crystal structure, or a polycrystalline structure.
nm or less, more preferably 1 nm to 50 nm, more preferably 1 nm to 30 nm
Further, it is more preferable to set the thickness to 3 nm or more and 20 nm or less.

The oxide semiconductor film 111 and the oxide semiconductor film 119 are formed using the same metal element.
An oxide semiconductor that can be used for the oxide semiconductor film 111 has an energy gap of 2 eV or more, preferably 2.5 eV or more, and more preferably 3 eV or more. By using an oxide semiconductor with such a wide energy gap, the off-state current of the transistor 103 can be reduced.

An oxide semiconductor applicable to the oxide semiconductor film 111 is preferably a metal oxide containing at least indium (In) or zinc (Zn), or preferably contains both In and Zn. In addition to the metal oxide, the oxide semiconductor preferably contains one or more stabilizers in order to reduce fluctuations in electrical characteristics of a transistor including the oxide semiconductor.

The stabilizer may be gallium (Ga), tin (Sn), hafnium (Hf), aluminum (Al), or zirconium (Zr). Other stabilizers include lanthanides such as lanthanum (La), cerium (Ce), and praseodymium (P).
r), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (
Examples of such elements include arsenic (Au), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

Examples of oxide semiconductors that can be used for the oxide semiconductor film 111 and the oxide semiconductor film 119 include
Examples of oxide semiconductors include indium oxide, tin oxide, zinc oxide, In-Zn oxides, which are oxides containing two kinds of metals, Sn-Zn oxides, Al-Zn oxides, Zn-
Mg-based oxides, Sn-Mg-based oxides, In-Mg-based oxides, In-Ga-based oxides, In-Ga-Zn-based oxides (also referred to as IGZO) which are oxides containing three types of metals, In
-Al-Zn oxide, In-Sn-Zn oxide, Sn-Ga-Zn oxide, Al-
Ga-Zn oxide, Sn-Al-Zn oxide, In-Hf-Zn oxide, In-Z
r-Zn oxide, In-Ti-Zn oxide, In-Sc-Zn oxide, In-Y-
Zn-based oxides, In-La-Zn-based oxides, In-Ce-Zn-based oxides, In-Pr-Z
n-type oxides, In-Nd-Zn-type oxides, In-Sm-Zn-type oxides, In-Eu-Zn
In-based oxides, In-Gd-Zn-based oxides, In-Tb-Zn-based oxides, In-Dy-Zn-based oxides, In-Ho-Zn-based oxides, In-Er-Zn-based oxides, In-Tm-Zn-based oxides, In-Yb-Zn-based oxides, In-Lu-Zn-based oxides, oxides containing four types of metals such as In-Sn-Ga-Zn-based oxides, In-Hf-Ga-Zn-based oxides, In-A
In-Ga-Zn based oxides, In-Sn-Al-Zn based oxides, In-Sn-Hf-Zn based oxides, and In-Hf-Al-Zn based oxides can be used.

Here, the In-Ga-Zn oxide means an oxide having In, Ga, and Zn as main components, and the ratio of In, Ga, and Zn does not matter. Also, metal elements other than In, Ga, and Zn may be contained.

Alternatively, the oxide semiconductor may be a material represented by InMO ₃ (ZnO) _m (m>0), where M represents one or more metal elements selected from Ga, Fe, Mn, and Co, or the above-mentioned element serving as a stabilizer.

For example, In:Ga:Zn=1:1:1 (=1/3:1/3:1/3), In:Ga:
Zn=2:2:1 (=2/5:2/5:1/5), or In:Ga:Zn=3:1:
Alternatively, an In-Ga-Zn-based metal oxide having an atomic ratio of In:Sn:Zn=1:1:1 (=1/3:1/3:1/3),
In:Sn:Zn=2:1:3 (=1/3:1/6:1/2) or In:Sn:Zn
It is preferable to use an In-Sn-Zn-based metal oxide having an atomic ratio of 2:1:5 (=1/4:1/8:5/8). Note that the atomic ratio of metal elements contained in the metal oxide includes an error of ±20% from the above atomic ratio.

However, the present invention is not limited to these, and any suitable atomic ratio may be used depending on the required semiconductor characteristics and electrical characteristics (field effect mobility, threshold voltage, variation, etc.). In order to obtain the required semiconductor characteristics, it is preferable to appropriately select the carrier density, impurity concentration, defect density, atomic ratio of metal elements to oxygen, interatomic distance, density, etc. For example, In-S
High field effect mobility can be obtained relatively easily with n-Zn oxides.
Even in the case of Ga—Zn-based oxides, the field effect mobility can be increased by lowering the defect density in the bulk.

The oxide semiconductor film 119 can be formed using an oxide semiconductor that can be used for the oxide semiconductor film 111. In addition, since the oxide semiconductor film 119 can be formed at the same time as the oxide semiconductor film 111, the oxide semiconductor film 119 contains a metal element of the oxide semiconductor included in the oxide semiconductor film 111.

The insulating films 129, 131, and 132 functioning as a protective insulating film of the transistor 103 and a dielectric film of the storage capacitor 105 are insulating films using a material that can be used for the gate insulating film 127. In particular, it is preferable that the insulating films 129 and 131 are oxide insulating films and the insulating film 132 is a nitride insulating film. Furthermore, the insulating film 132 is a nitride insulating film, which can prevent impurities such as hydrogen and water from entering the transistor 103 (particularly the oxide semiconductor film 111) from the outside. Note that a structure in which the insulating film 129 is not provided may be used.

One or both of the insulating films 129 and 131 are preferably oxide insulating films containing more oxygen than the oxygen required for the stoichiometric composition. In this manner, oxygen can be prevented from being released from the oxide semiconductor film 111 and the oxygen contained in the oxygen-excess region can be moved to the oxide semiconductor film 111, thereby reducing oxygen vacancies. For example,
By using an oxide insulating film having a release amount of oxygen molecules of 1.0× ¹⁰ molecules/cm ^or more as measured by thermal desorption spectroscopy (hereinafter referred to as TDS analysis),
The oxygen vacancies in the insulating film 129 and the insulating film 131 can be reduced.
In one or both of the above, a region containing oxygen in excess of the stoichiometric composition (oxygen excess region)
The presence of an oxygen-excess region at least in a region overlapping with the oxide semiconductor film 111 can prevent oxygen from being released from the oxide semiconductor film 111 and can move the oxygen contained in the oxygen-excess region to the oxide semiconductor film 111, thereby reducing oxygen vacancies.

In the case where the insulating film 131 is an oxide insulating film containing more oxygen than the oxygen that satisfies the stoichiometric composition, the insulating film 129 is preferably an oxide insulating film that transmits oxygen.
In this case, oxygen that has entered the insulating film 129 from the outside does not pass through the insulating film 129 at all, and some of the oxygen remains in the insulating film 129.
Some oxygen moves to the outside from the insulating film 129. Therefore, the insulating film 129 is preferably an oxide insulating film with a high diffusion coefficient of oxygen.

Further, since the insulating film 129 is in contact with the oxide semiconductor film 111, it is preferable that the insulating film 129 be an oxide insulating film that not only transmits oxygen but also can reduce the interface state density with the oxide semiconductor film 111. For example, the insulating film 129 is preferably an oxide insulating film that has a lower defect density than the insulating film 131. Specifically, the insulating film 129 has a g value of 2.001 (E'
The spin density of the insulating film 129 (g-center) is 3.0×10 ¹⁷ spins/cm ³ or less, preferably 5.0×10 ¹⁶ spins/cm ³ or less. Note that the spin density at g value=2.001 measured by electron spin resonance corresponds to the amount of dangling bonds present in the insulating film 129.

The thickness of the insulating film 129 can be set to 5 nm or more and 150 nm or less, preferably 5 nm or more and 50 nm or less, and more preferably 10 nm or more and 30 nm or less.
The thickness can be set to 30 nm or more and 500 nm or less, and preferably 150 nm or more and 400 nm or less.

In addition, the insulating film 129 provided over the oxide semiconductor film 111 is an oxide insulating film that transmits oxygen and can reduce the interface state density with the oxide semiconductor film 111, and the insulating film 131 is an oxide insulating film that includes an oxygen-excess region or an oxide insulating film that contains more oxygen than the stoichiometric composition. This makes it easy to supply oxygen to the oxide semiconductor film 111.
This makes it possible to prevent oxygen from being released from the oxide semiconductor film 111, and to cause oxygen contained in the insulating film 131 to move to the oxide semiconductor film 111 and fill oxygen vacancies in the oxide semiconductor film 111. As a result, the transistor 103 can be prevented from becoming normally-on.

Note that in the case where one or both of the insulating films 129 and 131 are formed using an oxide insulating film containing nitrogen, such as silicon oxynitride or silicon nitride oxide, the nitrogen concentration obtained by SIMS is
SIMS detection limit or more and less than 3×10 ²⁰ atoms/cm ³ , preferably 1×10 ¹⁸ a
The concentration of nitrogen in the oxide insulating film containing nitrogen is preferably greater than or equal to 1×10 ²⁰ atoms/cm ³ and less than or equal to 1×10 20 atoms/cm ^3. This can reduce the amount of nitrogen transferred to the oxide semiconductor film 111 included in the transistor 103. Furthermore, this can reduce the number of defects in the oxide insulating film itself containing nitrogen.

When the insulating film 132 is a nitride insulating film, one or both of the insulating films 129 and 131 are preferably insulating films having a barrier property against nitrogen. For example, a dense oxide insulating film can have a barrier property against nitrogen, and specifically, an oxide insulating film whose etching rate is 10 nm/min or less when 0.5 wt % hydrofluoric acid is used at 25° C. is preferably used.

As the insulating film 132, a nitride insulating film with a low hydrogen content can be provided. For example, the nitride insulating film has a hydrogen content of 5.0×
The nitride insulating film has a concentration of less than 10 ²¹ /cm ³ , preferably less than 3.0×10 ²¹ /cm ³ , and more preferably less than 1.0×10 ²¹ /cm ³ .

In addition, the nitride insulating film has excellent step coverage and is therefore useful as a protective insulating film for the transistor 103 .

The insulating film 132 has a thickness that can suppress the intrusion of impurities such as hydrogen and water from the outside, for example, from 50 nm to 200 nm, preferably from 50 nm to 150 nm, and further preferably from 50 nm to 100 nm.

In addition, by using a nitride insulating film as the insulating film 132 provided over the insulating film 131,
Impurities such as hydrogen and water can be prevented from entering the oxide semiconductor film 111 from the outside.
Furthermore, by providing a nitride insulating film with a low hydrogen content as the insulating film 132, change in the electrical characteristics of the transistor 103 can be suppressed.

Alternatively, a silicon oxide film formed by a CVD method using an organosilane gas may be provided between the insulating film 131 and the insulating film 132. The silicon oxide film has excellent step coverage and is therefore useful as a protective insulating film for the transistor 103.
The organic silane gas may be ethyl silicate (TEOS: chemical formula Si(OC ₂ H ₅ ) ₄ ), tetramethylsilane (TMS: chemical formula Si
(CH ₃ ) ₄ ), tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (SiH(OC ₂ H ₅ ) ₃ ), trisdimethylaminosilane (SiH(N(C
Silicon-containing compounds such as H ₃ ) ₂ ) ₃ ) can be used.

The pixel electrode 121 is formed using a light-transmitting conductive film. The light-transmitting conductive film is 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.

Substrate 150 can be made of a base material that can be applied to substrate 102.

The light-shielding film 152 is also called a black matrix, and is provided in a liquid crystal display device to suppress light leakage from a light source such as a backlight, and to suppress a decrease in contrast due to color mixing that occurs when performing color display using a color filter. The light-shielding film 152 can be provided using a commonly used material. For example, a metal or an organic resin containing a pigment can be used as a material having light-shielding properties. Note that the light-shielding film 152 is provided not only in the region overlapping with the transistor 103, but also in the pixel portion 10 such as the scanning line driver circuit 104 and the signal line driver circuit 106 (see FIG. 1 ).
It may be provided in an area other than 0.

Furthermore, a colored film having a function of transmitting light of a predetermined wavelength may be provided between the light-shielding films provided in each pixel in the pixel section 100. Furthermore, an overcoat film may be provided between the light-shielding film and the colored film and between the counter electrode and the counter electrode.

The opposing electrode 154 is made of an appropriate material that can be used for the pixel electrode 121.

The alignment film 156 and the alignment film 158 can be formed using a commonly used material such as polyamide.

The liquid crystal 160 may be a thermotropic liquid crystal, a low molecular weight liquid crystal, a polymer liquid crystal, a polymer dispersed liquid crystal,
Ferroelectric liquid crystals, antiferroelectric liquid crystals, etc. can be used. These liquid crystal materials exhibit a cholesteric phase, a smectic phase, a cubic phase, a chiral nematic phase, an isotropic phase, etc., depending on the conditions.

The liquid crystal 160 may be a liquid crystal that exhibits a blue phase without using an alignment film. The blue phase is one of the liquid crystal phases, and is a phase that appears immediately before a cholesteric liquid crystal transitions from a cholesteric phase to an isotropic phase when the temperature is increased. Since the blue phase appears only in a narrow temperature range, a liquid crystal composition mixed with a chiral agent is used to improve the temperature range. Note that the alignment film is formed of an organic resin, and the organic resin contains hydrogen, water, or the like, and therefore may degrade the electrical characteristics of the transistor of the semiconductor device according to one embodiment of the present invention. Therefore, by using the blue phase as the liquid crystal 160, the semiconductor device according to one embodiment of the present invention can be manufactured without using an organic resin, and a highly reliable semiconductor device can be obtained.

The liquid crystal element 108 is configured to switch between the pixel electrodes 12 according to the display mode of the liquid crystal element 108.
The configuration can be changed as appropriate, for example, by modifying the shapes of the electrode 1 and the counter electrode 154, or by forming protrusions called ribs.

<Method for Manufacturing Semiconductor Device>
Next, a method for manufacturing the above semiconductor device will be described with reference to FIGS.

First, the scanning line 107 and the capacitance line 115 are formed on the substrate 102, the insulating film 126 to be processed into the gate insulating film 127 later is formed so as to cover the scanning line 107 and the capacitance line 115, the oxide semiconductor film 111 is formed in the region of the insulating film 126 that overlaps with the scanning line 107, and the pixel electrode 1
An oxide semiconductor film 119 is formed so as to overlap with a region where the oxide semiconductor film 21 is formed (see FIG. 6A ).

The scanning line 107 and the capacitance line 115 can be formed by forming a conductive film using the above-listed materials, forming a mask on the conductive film, and processing the conductive film using the mask. The conductive film can be formed by various film formation methods such as evaporation, CVD, sputtering, and spin coating. The thickness of the conductive film is not particularly limited and can be determined in consideration of the formation time, the desired resistivity, and the like. The mask can be, for example, a resist mask formed by a first photolithography process. The conductive film can be processed by one or both of dry etching and wet etching.

The insulating film 126 can be formed using a material applicable to the gate insulating film 127 by various film formation methods such as a CVD method or a sputtering method.
When gallium oxide is applied to 7, MOCVD (Metal Organic Chemical Vapor Deposition) is used.
The insulating film 126 can be formed by a chemical vapor deposition (CVD) method.

The oxide semiconductor film 111 and the oxide semiconductor film 119 can be formed by forming an oxide semiconductor film using any of the oxide semiconductors listed above, forming a mask on the oxide semiconductor film, and processing the oxide semiconductor film by using the mask. Therefore, the oxide semiconductor film 111 and the oxide semiconductor film 119 are composed of the same metal element. The oxide semiconductor film can be formed by a sputtering method, a coating method, a pulsed laser deposition method, a laser ablation method, or the like. By using a printing method, the oxide semiconductor film 111 and the oxide semiconductor film 114 that are isolated from each other can be formed by a printing method.
9 can be formed directly on the gate insulating film 127. When the oxide semiconductor film is formed by a sputtering method, a power supply for generating plasma is an RF power supply, an AC
A power supply or a DC power supply can be appropriately used. A rare gas (typically argon), oxygen, or a mixed gas of a rare gas and oxygen can be appropriately used as the sputtering gas.
In the case of a mixed gas of a rare gas and oxygen, it is preferable to increase the gas ratio of oxygen to the rare gas. The target may be appropriately selected depending on the composition of the oxide semiconductor film to be formed. Note that the mask can be a resist mask formed by, for example, a second photolithography process. The oxide semiconductor film can be processed by one or both of dry etching and wet etching. Etching conditions (etching gas, etching solution, etching time, temperature, and the like) are appropriately set depending on the material so that the oxide semiconductor film can be etched into a desired shape.

After the oxide semiconductor films 111 and 119 are formed, heat treatment is preferably performed so that the oxide semiconductor films 111 and 119 are dehydrogenated or dehydrated.
The temperature of the heat treatment is typically 150° C. or higher and lower than the substrate distortion point, preferably 200° C.
The heat treatment is preferably performed at a temperature higher than or equal to 450° C., more preferably at a temperature higher than or equal to 300° C. and lower than or equal to 450° C. Note that the heat treatment may be performed on the oxide semiconductor film 111 and the oxide semiconductor film before they are processed into the oxide semiconductor film 119.

In the heat treatment, the heat treatment device is not limited to an electric furnace, and may be a device that heats the object to be treated by heat conduction or heat radiation from a medium such as a heated gas. For example,
GRTA (Gas Rapid Thermal Anneal) equipment, LRTA (La
Rapid Thermal Anneal (RTA) equipment such as
A LRTA apparatus can be used. The LRTA apparatus is an apparatus that heats the workpiece by radiating light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp, or a high-pressure mercury lamp. The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas.

The heat treatment may be performed in an atmosphere of nitrogen, oxygen, ultra-dry air (air with a water content of 20 ppm or less, preferably 1 ppm or less, and preferably 10 ppb or less), or a rare gas (argon, helium, etc.). Note that it is preferable that the nitrogen, oxygen, ultra-dry air, or rare gas does not contain hydrogen, water, or the like. After heating in an inert gas atmosphere, heating in an oxygen atmosphere may be performed. Note that the treatment time is 3 minutes to 24 hours.

Note that in the case where a base insulating film is provided between the substrate 102 and the scan line 107, the capacitance line 115, and the gate insulating film 127, the base insulating film can be formed of silicon oxide, silicon oxynitride, silicon nitride, silicon nitride oxide, gallium oxide, hafnium oxide, yttrium oxide, aluminum oxide, aluminum oxynitride, or the like. Note that by forming the base insulating film using silicon nitride, gallium oxide, hafnium oxide, yttrium oxide, aluminum oxide, or the like, it is possible to suppress diffusion of impurities, typically alkali metals, water, hydrogen, and the like, from the substrate 102 to the oxide semiconductor film 111. The base insulating film can be formed by a sputtering method or a CVD method.

Next, an opening 123 is formed in the insulating film 126 to reach the capacitance line 115, and a gate insulating film 127 is formed.
After forming the signal line 109 including the source electrode of the transistor 103, the transistor 10
Then, the conductive film 113 including the drain electrode of No. 3 and the conductive film 125 electrically connecting the oxide semiconductor film 119 and the capacitor line 115 are formed (see FIG. 6B ).

The opening 123 can be formed by forming a mask by a third photolithography process so that a part of a region of the insulating film 126 overlapping with the capacitance line 115 is exposed, and processing is performed using the mask. Note that the mask and the processing can be performed in the same manner as the scanning line 107 and the capacitance line 115.

The signal line 109, the conductive film 113, and the conductive film 125 can be formed by forming a conductive film using a material applicable to the signal line 109, the conductive film 113, and the conductive film 125, forming a mask over the conductive film by a fourth photolithography process, and processing the conductive film by using the mask. The mask and the processing can be performed in the same manner as the scan line 107 and the capacitance line 115. Note that after the signal line 109 and the conductive film 113 are formed, the oxide semiconductor film 111
By cleaning the surface of the transistor 103, it is possible to reduce fluctuations in the electrical characteristics of the transistor 103. For example, a diluted phosphoric acid solution can be used.
A phosphate solution diluted 2-fold can be used.

Next, the oxide semiconductor film 111, the oxide semiconductor film 119, the signal line 109, the conductive film 113,
An insulating film 128 is formed over the conductive film 125 and the gate insulating film 127, an insulating film 130 is formed over the insulating film 128, and an insulating film 133 is formed over the insulating film 130 (see FIG. 7A). Note that the insulating film 128, the insulating film 130, and the insulating film 133 are preferably formed in succession.
In this manner, impurities can be prevented from being mixed into the interfaces of the insulating film 128, the insulating film 130, and the insulating film 133.

The insulating film 128 can be formed by using a material applicable to the insulating film 129 and by various deposition methods such as a CVD method or a sputtering method.
The insulating film 133 can be formed using a material that can be used for the insulating film 132.

In the case where an oxide insulating film capable of reducing the interface state density with the oxide semiconductor film 111 is used as the insulating film 129, the insulating film 128 can be formed under the following formation conditions. Note that the case where a silicon oxide film or a silicon oxynitride film is formed as the oxide insulating film will be described here. The formation conditions are as follows:
The conditions are as follows: the temperature is maintained at 80° C. or higher and 400° C. or lower, and more preferably 200° C. or higher and 370° C. or lower; a deposition gas containing silicon as a raw material gas and an oxidizing gas are introduced into the processing chamber to set the pressure in the processing chamber to 20 Pa or higher and 250 Pa or lower, and more preferably 40 Pa or higher and 200 Pa or lower; and high-frequency power is supplied to an electrode provided in the processing chamber.

Representative examples of silicon-containing deposition gases include silane, disilane, trisilane, fluorinated silane, etc. Oxidizing gases include oxygen, ozone, nitrous oxide, nitrogen dioxide, etc.

In addition, by making the amount of oxidizing gas 100 times or more the amount of deposition gas containing silicon,
It is possible to reduce the hydrogen content in the insulating film 128 (insulating film 129) and also to reduce the dangling bonds in the insulating film 128 (insulating film 129). Since oxygen moving from the insulating film 130 (insulating film 131) may be captured by the dangling bonds in the insulating film 128 (insulating film 129), when the dangling bonds in the insulating film 128 (insulating film 129) are reduced, the insulating film 130 (insulating film 131) can be easily oxidized.
1) can be efficiently transferred to the oxide semiconductor film 111, and oxygen vacancies in the oxide semiconductor film 111 can be reduced. As a result, the amount of hydrogen mixed into the oxide semiconductor film 111 can be reduced, and oxygen vacancies in the oxide semiconductor film 111 can be reduced.

When the insulating film 131 is an oxide insulating film including the above-described oxygen excess region or an oxide insulating film including more oxygen than the oxygen that satisfies the stoichiometric composition, the insulating film 130 can be formed under the following formation conditions. Note that the case where a silicon oxide film or a silicon oxynitride film is formed as the oxide insulating film will be described here. The formation conditions are as follows: a substrate placed in an evacuated processing chamber of a plasma CVD apparatus is heated to 180° C. or higher and 260° C. or lower, more preferably 180° C. or lower.
The temperature was kept at 230° C. or higher, and the source gas was introduced into the processing chamber to reduce the pressure in the processing chamber to 10
The pressure is set to 0 Pa or more and 250 Pa or less, more preferably 100 Pa or more and 200 Pa or less, and high-frequency power of 0.17 W/cm ² or more and 0.5 W/cm ² or less, more preferably 0.25 W/cm ² or more and 0.35 W/cm ² or less is supplied to the electrode provided in the processing chamber.

The source gas for the insulating film 130 may be a source gas that can be used to form the insulating film 128 .

As a forming condition of the insulating film 130, by supplying high-frequency power with the above power density in a process chamber with the above pressure, the decomposition efficiency of the source gas in the plasma is increased, oxygen radicals are increased, and oxidation of the source gas progresses, so that the oxygen content in the insulating film 130 becomes higher than the stoichiometric composition. However, when the substrate temperature is the above temperature, the bonding force between silicon and oxygen is weak, and therefore, part of the oxygen is desorbed by heating. As a result, an oxide insulating film that contains more oxygen than oxygen satisfying the stoichiometric composition and from which part of the oxygen is desorbed by heating can be formed. In addition, the insulating film 128 is provided over the oxide semiconductor film 111. Therefore, in the process of forming the insulating film 130, the insulating film 128 serves as a protective film for the oxide semiconductor film 111. As a result, even when the insulating film 130 is formed using high-frequency power with high power density, damage to the oxide semiconductor film 111 can be suppressed.

In addition, since the amount of oxygen desorbed by heating can be increased by increasing the thickness of the insulating film 130, the insulating film 130 is preferably provided to be thicker than the insulating film 128. By providing the insulating film 128, good coverage can be achieved even in the case where the insulating film 130 is provided to be thick.

When the insulating film 132 is a nitride insulating film with a low hydrogen content, the insulating film 133 can be formed under the following formation conditions. Note that a case where a silicon nitride film is formed as the nitride insulating film will be described here. The formation conditions are as follows: a substrate placed in an evacuated processing chamber of a plasma CVD apparatus is heated to 80° C. to 400° C., more preferably 200° C. to 37° C.
The conditions are as follows: the temperature is kept at 0° C. or less, a source gas is introduced into the processing chamber to set the pressure in the processing chamber to 100 Pa or more and 250 Pa or less, preferably 100 Pa or more and 200 Pa or less, and high frequency power is supplied to an electrode provided in the processing chamber.

As the source gas of the insulating film 133, a deposition gas containing silicon, nitrogen, and ammonia are preferably used. Typical examples of the deposition gas containing silicon include silane, disilane, trisilane, and fluorinated silane. The flow rate of nitrogen is preferably 5 to 50 times, preferably 10 to 50 times, that of ammonia. Note that the use of ammonia as the source gas can promote decomposition of the deposition gas containing silicon and nitrogen. This is because ammonia is dissociated by plasma energy or thermal energy, and the energy generated by the dissociation contributes to the decomposition of the bonds of the deposition gas molecules containing silicon and the bonds of the nitrogen molecules. In this way, a silicon nitride film having a low hydrogen content and capable of suppressing the intrusion of impurities such as hydrogen and water from the outside can be formed.

In addition, when a silicon oxide film formed by a CVD method using an organosilane gas is provided between the insulating films 131 and 132, the silicon oxide film is formed on the insulating film 130 by a CVD method using the organosilane gas listed above.

After at least the insulating film 130 is formed, a heat treatment is performed to form the insulating film 128 or the insulating film 13
At least oxygen contained in the oxide semiconductor film 111 is moved to the oxide semiconductor film 111.
Note that the heat treatment can be performed as appropriate with reference to the details of the heat treatment for dehydrogenating or dehydrating the oxide semiconductor films 111 and 119.

In addition, one of the preferable procedures for forming the transistor 103 is to form, as the insulating film 130, an oxide insulating film that contains more oxygen than the oxygen that satisfies the stoichiometric composition and from which some of the oxygen is released by heating, perform heat treatment at 350° C. after forming the insulating film 130, form a silicon oxide film by a CVD method using any of the organosilane gases listed above and keeping the substrate temperature at 350° C., and form, as the insulating film 132, a nitride insulating film with a low hydrogen content with the substrate temperature set to 350° C.

Next, a mask is formed in a region of the insulating film 128, the insulating film 130, and the insulating film 133 that overlaps with the conductive film 113 by a fifth photolithography process.
The conductive film 113 is etched to form an opening 117 reaching the conductive film 113, and the insulating films 129, 131, and 132 are also formed (see FIG. 7B). Next, the pixel electrode 121 is formed over the opening 117 and the insulating film 132 (see FIG. 5).

The opening 117 can be formed in the same manner as the opening 123. The pixel electrode 121 can be formed by forming a conductive film that is in contact with the conductive film 113 through the opening 117 using the above-listed materials, forming a mask on the conductive film by a sixth photolithography process, and processing the conductive film using the mask. Note that the mask and the processing can be performed in the same manner as the scanning line 107 and the capacitance line 115.

Next, an alignment film 158 is formed on the insulating film 132 and the pixel electrodes 121.
A light-shielding film 152 is formed on the substrate 102. A counter electrode 154 is formed so as to cover the light-shielding film 152, and an alignment film 156 is formed on the counter electrode 154. A liquid crystal 160 is provided on the alignment film 158, and a substrate 150 is provided on the substrate 102 so that the alignment film 156 is in contact with the liquid crystal 160, and the substrate 102 and the substrate 150 are fixed together by a sealant (not shown).

The alignment films 156 and 158 can be formed by appropriately using various film formation methods such as spin coating and printing using the above-mentioned materials.

The light-shielding film 152 can be formed by depositing the above-listed materials by a sputtering method and processing the film using a mask.

The counter electrode 154 can be formed by using a material that can be used for the pixel electrode 121 and by utilizing various film formation methods such as a CVD method or a sputtering method.

The liquid crystal 160 can be provided directly on the alignment film 158 by a dispenser method (dropping method). Alternatively, the liquid crystal 160 can be applied by using capillary action or the like after the substrate 102 and the substrate 150 are bonded together.
In addition, the liquid crystal 160 may be provided with an alignment film 156 to facilitate alignment.
In addition, it is preferable to perform a rubbing process on the alignment film 158 .

Through the above steps, a semiconductor device which is one embodiment of the present invention can be manufactured (see FIG. 5).

<Variation 1>
In the semiconductor device according to one embodiment of the present invention, the connection between the oxide semiconductor film that functions as one electrode of a storage capacitor and a capacitor line can be changed as appropriate. For example, in order to further increase the aperture ratio, a structure in which the semiconductor film is in direct contact with the capacitor line without an intermediate conductive film can be used. A specific example of this structure will be described with reference to FIGS.

In the drawings showing the modified examples below, the substrate 150, the light-shielding film 152, the counter electrode 154, the alignment film 156, the alignment film 158, and the liquid crystal 160 are omitted for clarity. Also, in the drawings showing the modified examples, the reference characters used in Fig. 4 or Fig. 5 are used as appropriate. In the modified examples below, only the differences from the structures shown in Fig. 4 and Fig. 5 will be described.

A specific example of this structure will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a top view of the pixel 101, and Fig. 9(A) is a cross-sectional view between dashed dotted lines A1-A2 and B1-B2 in Fig. 8.

8 and 9, the oxide semiconductor film 119 functioning as one electrode of the storage capacitor 145 is in direct contact with the capacitor line 115 through an opening 143. As in the storage capacitor 105 shown in FIGS. 4 and 5, the oxide semiconductor film 119 and the capacitor line 115 are in direct contact without the conductive film 125 therebetween, and the conductive film 125 serving as a light-shielding film is not formed, so that the aperture ratio of the pixel can be further increased. This is because the oxide semiconductor film 119 in FIG. 6A is
Before the formation of the oxide semiconductor films 111 and 119, an opening for exposing the capacitance line 115 may be formed, and then the oxide semiconductor films 111 and 119 may be formed.

9, the opening 143 is provided only on the capacitance line 115. However, as shown in FIG. 10, the opening 143 may be formed in the gate insulating film 127 so that a part of each of the capacitance line 115 and the substrate 102 is exposed.
6A , before the oxide semiconductor films 111 and 119 are formed, a gate insulating film 127 is formed so that each of the capacitance line 115 and the substrate 102 is partially exposed, and then the oxide semiconductor films 111 and 119 are formed over the capacitance line 115 and the substrate 102 to increase the area where the oxide semiconductor film 119 is in contact with the capacitance line 115.
As a result, the aperture ratio can be increased, and the conductivity of the oxide semiconductor film 119 is increased. Thus, the oxide semiconductor film 119 can be easily brought into a conductive state, so that the storage capacitor 146 can easily function.

<Modification 2>
In a semiconductor device according to one embodiment of the present invention, a connection between an oxide semiconductor film that functions as one electrode of a storage capacitor and a capacitor line can be changed as appropriate. For example, in order to reduce contact resistance between the semiconductor film and a conductive film, the conductive film can be provided in contact with the semiconductor film along its outer periphery. A specific example of this structure will be described with reference to FIGS. 11 and 12. Note that FIG. 11 is a top view of a pixel 101 having this structure, FIG. 12A is a cross-sectional view taken along dashed lines A1-A2 and B1-B2 in FIG. 11, and FIG. 12B is a cross-sectional view taken along dashed lines C1-C2 in FIG. 11.

In the pixel 101 shown in FIGS. 11 and 12, the conductive film 167 is a
9 and is in contact with the capacitance line 115 through the opening 123. The conductive film 167 is provided so as to cover an end portion of the oxide semiconductor film 119. The conductive film 167 can be formed by utilizing the formation processes of the signal line 109, the conductive film 113, and the conductive film 125. Since the conductive film 167 may have a light-blocking property, it is preferable to form the conductive film 167 in a loop shape. Note that as the contact area between the conductive film 167 and the oxide semiconductor film 119 increases, the conductivity of the oxide semiconductor film 119 increases and the oxide semiconductor film 119 can be easily brought into a conductive state, so that the conductive film 167 easily functions as one electrode of the storage capacitor 165.

In addition, in the pixel 101 illustrated in FIGS. 11 and 12, the oxide semiconductor film 119 and the capacitor line 115 are in contact with the conductive film 167, so that the shape of the oxide semiconductor film 119 can be changed as appropriate.

Alternatively, the conductive film 167 may be provided in contact with the oxide semiconductor film 119 with the loop-shaped portion being separated.

<Modification 3>
In the semiconductor device according to one embodiment of the present invention, the connection between the oxide semiconductor film which functions as one electrode of a storage capacitor and a capacitor line can be changed as appropriate. For example, as in the pixel 101 illustrated in FIGS. 13 and 14 , the capacitor line 1
75 can be formed.

13 shows a top view of the pixel 101 having this structure, and FIG. 14 shows the pixel 101 along the dashed line A1-
13A and 13B are cross-sectional views taken along dashed lines B1-B2 and D1-D2, respectively.

The capacitance line 175 is provided so as to extend in a direction parallel to the signal line 109.
The signal line driver circuit 106 and the capacitor line 175 are electrically connected to the signal line driver circuit 106 (see FIG. 1A).

In the pixel 101 shown in FIGS. 13 and 14 , a region where the oxide semiconductor film 119 and the pixel electrode 121 overlap with each other via the insulating films 129, 131, and 132 provided over the oxide semiconductor film 119 serves as a storage capacitor 174.

When a capacitance line is provided extending in a direction parallel to the signal line 109, like the capacitance line 175, it is preferable that the pixel has a shape in which the side parallel to the scanning line 107 is longer than the side parallel to the signal line 109, like the pixel 101 shown in Fig. 13. This is because, compared to a pixel having a shape in which the side parallel to the signal line 109 is longer than the side parallel to the scanning line 107, it is possible to reduce the area where the pixel electrode 121 and the capacitance line 175 overlap, thereby improving the aperture ratio.

<Modification 4>
In a semiconductor device according to one embodiment of the present invention, one electrode of a storage capacitor and a capacitor line can be formed using a semiconductor film (specifically, an oxide semiconductor film).
5. Note that only the oxide semiconductor film 198, which is different from the oxide semiconductor film 119 and the capacitance line 115 described with reference to FIG. 4 and FIG. 5, will be described here. FIG. 15 is a top view of a pixel 101 according to this modification. In the pixel 101 shown in FIG. 15, an oxide semiconductor film 198 serving as one electrode of a storage capacitor 197 and a capacitance line is provided. The oxide semiconductor film 198 has a region extending in a direction parallel to the signal line 109, and the region functions as a capacitance line. In the oxide semiconductor film 198, a region overlapping with the pixel electrode 121 functions as one electrode of the storage capacitor 197. Note that the oxide semiconductor film 198 can be formed by utilizing the process of forming the oxide semiconductor film 111 included in the transistor 103 provided in the pixel 101 shown in FIG. 15.

The oxide semiconductor film 198 can be provided as one oxide semiconductor film in each pixel 101 so as to overlap with the scan line 107.
The oxide semiconductor film can be provided as a continuous film without any gaps in all the pixels 101 in a row.

In addition, when the oxide semiconductor film 198 is provided as a continuous oxide semiconductor film without being spaced apart in all the pixels 101 in one row, the oxide semiconductor film 198 overlaps with the scan line 107.
Due to the influence of a change in potential of the scanning line 107, the scanning line 107 may not function as a capacitance line or one electrode of a storage capacitor 197. Therefore, as shown in FIG. 15 , the oxide semiconductor film 198 is provided at a distance in each pixel 101.
It is preferable that the conductive film 199 be used for electrical connection, which can be formed by utilizing the formation steps of the conductive films 09 and 113 .

15 , the region of the oxide semiconductor film 198 functioning as a capacitance line extends in a direction parallel to the signal line 109, but the region may extend in a direction parallel to the scanning line 107. Note that in the case where the region of the oxide semiconductor film 198 functioning as a capacitance line extends in a direction parallel to the scanning line 107, the transistor 103 and the storage capacitor 19
In No. 7, it is necessary to provide an insulating film between the oxide semiconductor film 111 and the signal line 109 and between the oxide semiconductor film 198 and the conductive film 113 to electrically isolate them from each other.

As described above, by providing an oxide semiconductor film as one electrode of a storage capacitor and a capacitor line in the pixel as in the pixel 101 illustrated in FIG. 15, the aperture ratio of the pixel can be improved.

<Modification 5>
In the pixel 101 described as the above modification, the pixel electrode 121 and the conductive film 113
In order to reduce the parasitic capacitance generated between the pixel electrode 121 and the conductive film 167 or between the pixel electrode 121 and the conductive film 167, an organic insulating film can be provided in a region where the parasitic capacitance is generated. In other words, the organic insulating film can be provided partially in the pixel 101.

The organic insulating film can be made of a photosensitive or non-photosensitive organic resin, such as an acrylic resin, a benzocyclobutene resin, an epoxy resin, a siloxane resin, or a polyamide.

In order to partially provide the organic insulating film, after forming the insulating film using the materials listed above, the insulating film may need to be processed. The method for forming the organic insulating film is not particularly limited and can be appropriately selected depending on the material used. For example, spin coating, dipping, spray coating, droplet discharge method (inkjet method), screen printing, offset printing, etc. can be applied. In addition, by using a photosensitive organic resin as the organic insulating film, a resist mask is not required when forming the organic insulating film, and the process can be simplified.

<Modification 6>
In addition, in the semiconductor device according to one embodiment of the present invention, the configuration of the capacitance line can be changed as appropriate. This structure will be described with reference to Fig. 16. Note that, compared to the capacitance line 115 described in Fig. 4, this structure is different in that the capacitance line is located between two adjacent pixels.

FIG. 16 is a top view of a pixel 401_1 and a pixel 401_2 adjacent to each other in the extension direction of a signal line 409.

The scanning line 407_1 and the scanning line 407_2 are parallel to each other and extend in a direction substantially perpendicular to the signal line 109. A capacitance line 415 is provided between the scanning line 407_1 and the scanning line 407_2 and parallel to the scanning line 407_1 and the scanning line 407_2. Note that the capacitance line 415 is connected to a storage capacitance 405_1 provided in the pixel 401_1 and a storage capacitance 405_2 provided in the pixel 401_2.
The top shape of the capacitor _2 and the arrangement positions of the components are symmetrical with respect to the capacitor line 415.

The pixel 401_1 includes a transistor 403_1, a pixel electrode 421_1 connected to the transistor 403_1, and a storage capacitor 405_1.

The transistor 403_1 is provided in a region where the scan line 407_1 and the signal line 409 intersect. The transistor 403_1 includes at least an oxide semiconductor film 411_1 having a channel formation region, a gate electrode, a gate insulating film (not shown in FIG. 16 ), a source electrode, and a drain electrode.
A region of the signal line 409 overlapping with the oxide semiconductor film 411_1 functions as a gate electrode of the transistor 403_1. A region of the signal line 409 overlapping with the oxide semiconductor film 411_1 functions as a source electrode of the transistor 403_1. A region of the conductive film 413_1 overlapping with the oxide semiconductor film 411_1 functions as a drain electrode of the transistor 403_1.
And the pixel electrode 421_1 is connected at the opening 417_1.

The storage capacitor 405_1 is electrically connected to the capacitor line 415 through a conductive film 425 provided in an opening 423. The storage capacitor 405_1 includes an oxide semiconductor film 419_1 formed using a light-transmitting oxide semiconductor, a light-transmitting pixel electrode 421_1, and a light-transmitting insulating film (not shown in FIG. 16 ) included in the transistor 403_1 as a dielectric film. That is, the storage capacitor 405_1 has a light-transmitting property.

The pixel 401_2 includes a transistor 403_2 and a storage capacitor 405_2 connected to the transistor 403_2.

The transistor 403_2 is provided in a region where the scan line 407_2 and the signal line 409 intersect. The transistor 403_2 includes at least an oxide semiconductor film 411_2 having a channel formation region, a gate electrode, a gate insulating film (not shown in FIG. 16 ), and a source electrode and a drain electrode. Note that a region of the scan line 407_2 overlapping with the oxide semiconductor film 411_2 functions as a gate electrode of the transistor 403_2. A region of the signal line 409 overlapping with the oxide semiconductor film 411_2 functions as a gate electrode of the transistor 403_2.
A region of the conductive film 413_2 overlapping with the oxide semiconductor film 411_2 functions as a drain electrode of the transistor 403_2.
2 and the pixel electrode 421_2 are connected at the opening 417_2.

The storage capacitor 405_2 is electrically connected to the capacitor line 415 through a conductive film 425 provided in an opening 423, similar to the storage capacitor 405_1. The storage capacitor 405_2 includes an oxide semiconductor film 419_2 made of an oxide semiconductor, a pixel electrode 421_2, and an insulating film (not shown in FIG. 16 ) included in the transistor 403_2 as a dielectric film. The oxide semiconductor film 419_2, the pixel electrode 421_2, and the dielectric film each have a light-transmitting property, so that the storage capacitor 405_2 has a light-transmitting property.

Note that the transistor 403_1, the transistor 403_2, and the storage capacitor 405
5, and therefore will not be described here. For the transistor 403_1 and the transistor 403_2, and the storage capacitors 405_1 and 405_2, the reference symbols used to describe the transistor 103 and the storage capacitor 105 can be used as appropriate.

In the top view, a capacitance line is provided between two adjacent pixels, and the storage capacitors included in each pixel are connected to the capacitance line, thereby making it possible to reduce the number of capacitance lines, and as a result, it is possible to further increase the aperture ratio of the pixels compared to a structure in which a capacitance line is provided for each pixel.

<Modification 7>
In the semiconductor device according to one embodiment of the present invention, the shape of a transistor provided in a pixel is not limited to the shape of the transistor shown in the above modified example, and can be changed as appropriate. For example, the source electrode of the transistor included in the signal line 109 may be U-shaped (C-shaped, U-shaped, or horseshoe-shaped) and may surround a conductive film including a drain electrode. By using such a shape, a sufficient channel width can be ensured even if the area of the transistor is small, and the amount of drain current (also referred to as on-current) that flows when the transistor is conductive can be increased.

<Variation 8>
In the pixel 101, the pixel 401_1, and the pixel 401_2 described as the above modified example,
Although a transistor in which the oxide semiconductor film 111 is located between the gate insulating film 127, the signal line 109 including a region functioning as a source electrode, and the conductive film 113 including a region functioning as a drain electrode is used, a transistor in which the oxide semiconductor film 111 is located between the insulating film 129 and the signal line 109 including a region functioning as a source electrode and the conductive film 113 including a region functioning as a drain electrode can be used instead.

<Modification 9>
In the pixel 101, the pixel 401_1, and the pixel 401_2 described as the above modified example,
Although a channel-etched transistor is illustrated as the transistor 103, a channel-protective transistor can be used instead. By providing the channel protective film, the surface of the oxide semiconductor film 111 is not exposed to an etchant or an etching gas used in the process of forming the signal line 109 and the conductive film 113, and impurities between the oxide semiconductor film 111 and the channel protective film can be reduced. As a result, leakage current flowing between the source electrode and the drain electrode of the transistor 103 can be reduced.

<Modification 10>
In the pixel 101, the pixel 401_1, and the pixel 401_2 described as the above modified example,
Although a transistor having one gate electrode is illustrated as the transistor 103, a transistor having two gate electrodes opposed to each other with an oxide semiconductor film 111 interposed therebetween (
A dual gate transistor can be used.

The dual-gate transistor includes a conductive film (also referred to as a backgate electrode) over the insulating film 129 of the transistor 103 described in this embodiment. The conductive film overlaps with at least a channel formation region of the oxide semiconductor film 111. For example, the conductive film is formed so that the width of the conductive film in the channel length direction is larger than that of the signal line 10 including a region that functions as a source electrode of the transistor.
The conductive film 111 may have a shape shorter than the width between the source electrode 109 and the conductive film 113 functioning as a drain electrode. By providing the conductive film at a position overlapping with a channel formation region of the oxide semiconductor film 111, the potential of the conductive film is preferably set to the minimum potential of a video signal input to the signal line 109. As a result, a current flowing between the source electrode and the drain electrode can be controlled on a surface of the oxide semiconductor film 111 facing the conductive film, and variation in electrical characteristics of the transistor can be reduced. Furthermore, by providing the conductive film, the influence of a change in the surrounding electric field on the oxide semiconductor film 111 can be reduced, and the reliability of the transistor 103 can be improved.

The conductive film can be formed using the same material and method as those of the scan line 107, the signal line 109, the pixel electrode 121, and the like. In addition, the conductive film can be formed by utilizing the process for forming the pixel electrode 121. As described above, by using a semiconductor film formed in the same formation process as the oxide semiconductor included in the transistor as one electrode of the storage capacitor, a semiconductor device having a storage capacitor with increased aperture ratio and increased charge capacitance can be manufactured.
Moreover, by increasing the aperture ratio, a semiconductor device with excellent display quality can be obtained.

Furthermore, a transistor in a pixel is a transistor using an oxide semiconductor, and an oxide semiconductor film included in the transistor is an oxide semiconductor film in which oxygen vacancies are reduced and impurities such as hydrogen and nitrogen are reduced, whereby a semiconductor device with favorable electrical characteristics can be obtained.

Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiments.

(Embodiment 2)
In this embodiment, one mode in which the transistor and the storage capacitor included in the semiconductor device described in the above embodiment can be applied to an oxide semiconductor film that is a semiconductor film will be described.

The oxide semiconductor film may be an oxide semiconductor having a crystalline portion (C Axis Aligned Cryogenic Semiconductor) in addition to an amorphous oxide semiconductor, a single crystal oxide semiconductor, or a polycrystalline oxide semiconductor.
It is preferable that the insulating layer 100 be made of a stalemate oxide semiconductor (CAAC-OS).

The CAAC-OS film is one of oxide semiconductor films having a plurality of crystal parts, and most of the crystal parts fit within a cube with one side less than 100 nm.
The crystal parts in the OS film may be contained within a cube having one side of less than 10 nm, less than 5 nm, or less than 3 nm. The CAAC-OS film has a characteristic of having a lower density of defect states than a microcrystalline oxide semiconductor film. The CAAC-OS film is described in detail below.

The CAAC-OS film was observed using a transmission electron microscope (TEM).
When observed with a CT microscope, it is not possible to confirm clear boundaries between crystal parts, i.e., grain boundaries.
It can be said that the AAC-OS film is less susceptible to a decrease in electron mobility due to grain boundaries.

When the CAAC-OS film is observed by a TEM from a direction approximately parallel to the sample surface (cross-sectional TEM observation), it can be seen that metal atoms are arranged in layers in the crystal parts. Each layer of metal atoms has a shape that reflects the unevenness of the surface (also referred to as the surface on which the CAAC-OS film is formed) or the top surface of the CAAC-OS film, and is arranged in parallel to the surface on which the CAAC-OS film is formed or the top surface.

On the other hand, the CAAC-OS film was observed by TEM from a direction approximately perpendicular to the sample surface (plane T
When observed by EM, it can be seen that the metal atoms are arranged in triangular or hexagonal shapes in the crystal parts. However, no regularity is observed in the arrangement of the metal atoms between different crystal parts.

Cross-sectional and planar TEM observations reveal that the crystal parts of the CAAC-OS film have orientation.

X-ray diffraction (XRD) of the CAAC-OS film
When the structure was analyzed using the device, for example, a CAAC-OS having InGaZnO ₄ crystals was found.
In an out-of-plane analysis of the film, a peak may appear at a diffraction angle (2θ) of approximately 31°. This peak is attributed to the (009) plane of the InGaZnO ₄ crystals, which confirms that the crystals of the CAAC-OS film have c-axis orientation, and the c-axis faces a direction approximately perpendicular to the surface on which the film is formed or the top surface.

On the other hand, in-p diffraction is performed by irradiating the CAAC-OS film with X-rays from a direction approximately perpendicular to the c-axis.
In the analysis by the lane method, a peak may appear when 2θ is around 56°. This peak is attributed to the (110) plane of the InGaZnO ₄ crystal. In the case of a single crystal oxide semiconductor film of InGaZnO ₄ , 2θ is fixed at around 56°, and the normal vector of the sample plane is set as the axis (φ axis).
When the analysis (φ scan) is performed while rotating the sample at 2θ, six peaks attributable to a crystal plane equivalent to the (110) plane are observed. In contrast, in the case of the CAAC-OS film, no clear peaks appear even when φ scan is performed with 2θ fixed at around 56°.

From the above, it can be seen that the a-axis and b-axis orientations are irregular between different crystal parts in the CAAC-OS film, but the film has a c-axis orientation, and the c-axis is parallel to the normal vector of the surface on which the film is formed or the top surface. Therefore, each layer of metal atoms arranged in layers confirmed by the above-mentioned cross-sectional TEM observation is a plane parallel to the a-b plane of the crystal.

The crystalline parts are formed when the CAAC-OS film is formed or when a crystallization treatment such as heat treatment is performed. As described above, the c-axis of the crystal is oriented in a direction parallel to the normal vector of the surface on which the CAAC-OS film is formed or the top surface. Therefore, for example, when the shape of the CAAC-OS film is changed by etching or the like, the c-axis of the crystal may not be parallel to the normal vector of the surface on which the CAAC-OS film is formed or the top surface.

The degree of crystallinity in the CAAC-OS film does not have to be uniform.
When the crystalline portion of the film is formed by crystal growth from the vicinity of the top surface of the CAAC-OS film, the region near the top surface may have a higher degree of crystallinity than the region near the surface on which the film is formed.
When an impurity is added to an AC-OS film, the degree of crystallinity of a region to which the impurity is added changes, and a region with a different degree of crystallinity may be formed.

Note that the out-of-plane phase of the CAAC-OS film containing InGaZnO ₄ crystals
In the analysis by the method, in addition to the peak when 2θ is around 31°, a peak may also appear when 2θ is around 36°. The peak when 2θ is around 36° indicates that crystals without c-axis orientation are contained in part of the CAAC-OS film. It is preferable that the CAAC-OS film shows a peak when 2θ is around 31° and does not show a peak when 2θ is around 36°.

There are three methods for forming CAAC-OS:

The first method is a method in which an oxide semiconductor film is formed at a film formation temperature of 100° C. or higher and 450° C. or lower, thereby forming crystal parts in which the c-axes of crystal parts included in the oxide semiconductor film are aligned in a direction parallel to the normal vector of the surface on which the film is formed or the normal vector of the surface.

The second method is a method in which an oxide semiconductor film is formed to a small thickness and then heat treatment is performed at a temperature higher than or equal to 200° C. and lower than or equal to 700° C., thereby forming crystal parts in which the c-axes of crystal parts included in the oxide semiconductor film are aligned in a direction parallel to the normal vector of the surface on which the film is formed or the normal vector of the surface.

The third method is to form a first oxide semiconductor film to a thin thickness, and then heat the film at 200° C. or higher for up to 700° C.
This method involves performing heat treatment at 0.degree. C. or less, and then forming a second oxide semiconductor film, thereby forming crystal parts in which the c-axes of crystal parts included in the oxide semiconductor film are aligned in a direction parallel to the normal vector of the formation surface or the normal vector of the surface.

A transistor in which the CAAC-OS is used for its oxide semiconductor film has small change in its electrical characteristics due to irradiation with visible light or ultraviolet light, and thus has good reliability.

In addition, the CAAC-OS is preferably formed by a sputtering method using a polycrystalline oxide semiconductor sputtering target. When ions collide with the sputtering target, a crystalline region included in the sputtering target may be cleaved from the a-b plane and peeled off as a plate-like or pellet-like sputtering particle having a surface parallel to the a-b plane. In this case, the plate-like or pellet-like sputtering particle may be
By reaching the deposition surface while maintaining the crystalline state, a CAAC-OS film can be deposited.

In addition, it is preferable to apply the following conditions to form a CAAC-OS film.

By reducing the amount of impurities introduced during film formation, it is possible to prevent the crystal state from being destroyed by impurities. For example, the concentration of impurities (hydrogen, water, carbon dioxide, nitrogen, etc.) present in the film formation chamber can be reduced.
In addition, the impurity concentration in the deposition gas may be reduced. Specifically, a deposition gas having a dew point of −80° C. or less, preferably −100° C. or less, may be used.

In addition, by increasing the heating temperature of the deposition surface (e.g., the substrate heating temperature) during deposition, migration of sputtered particles occurs after the deposition surface is reached. Specifically, the deposition surface is heated to a temperature of 100° C. to 740° C., preferably 150° C. to 500° C.
By increasing the temperature of the deposition surface during deposition, when the plate-shaped or pellet-shaped sputtered particles reach the deposition surface, migration occurs on the deposition surface, and the flat surfaces of the sputtered particles adhere to the deposition surface.

It is also preferable to increase the oxygen ratio in the deposition gas and optimize the power to reduce plasma damage during deposition. The oxygen ratio in the deposition gas is 30% by volume or more, preferably 100% by volume or more.
Expressed as volume percent.

As an example of a sputtering target, an In-Ga-Zn-O compound target will be described below.

InO _X powder, GaO _Y powder, and ZnO _Z powder are mixed in a predetermined molar ratio, pressurized, and then heated at a temperature of 1000° C. to 1500° C. to obtain polycrystalline In—Ga
-Zn-based metal oxide target. The pressure treatment may be performed while cooling (or cooling), or while heating. X, Y, and Z are any positive numbers. Here, the predetermined molar ratio is, for example, 2:2:1, 8:4:3, 3:1:1, 1:1:1, 4:2:3, or 3:1:2 for the InO _X powder, GaO _Y powder, and ZnO _Z powder. The type of powder and the molar ratio of the powders to be mixed may be appropriately changed depending on the sputtering target to be produced.

The oxide semiconductor film may have a structure in which a plurality of oxide semiconductor films are stacked. For example,
The oxide semiconductor film may be a stack of a first oxide semiconductor film and a second oxide semiconductor film, and the first oxide semiconductor film and the second oxide semiconductor film may be formed using metal oxides having different atomic ratios. For example, one of an oxide containing two types of metals, an oxide containing three types of metals, and an oxide containing four types of metals may be used for the first oxide semiconductor film, and an oxide containing two types of metals, an oxide containing three types of metals, or an oxide containing four types of metals different from that of the first oxide semiconductor film may be used for the second oxide semiconductor film.

The oxide semiconductor film may have a two-layer structure, and the first oxide semiconductor film and the second oxide semiconductor film may be made to contain the same elements but have different atomic ratios. For example, the atomic ratio of the first oxide semiconductor film is In:Ga:Zn=3:1:2, and the atomic ratio of the second oxide semiconductor film is In:Ga:Zn=3:1:2.
The atomic ratio of the first oxide semiconductor film may be In:Ga:Zn=1:1:1.
The atomic ratio of the second oxide semiconductor film was In:Ga:Zn=2:1:3.
Alternatively, the atomic ratio may be 1:3:2. Note that the atomic ratio of each oxide semiconductor film includes a variation of ±20% of the above atomic ratio as an error.

At this time, the first oxide semiconductor film and the second oxide semiconductor film, whichever is closer to the gate electrode (
The atomic ratio of In to Ga in the oxide semiconductor film on the side closer to the gate electrode (channel side) is preferably In≧Ga. The atomic ratio of In to Ga in the oxide semiconductor film on the side farther from the gate electrode (back channel side) is preferably In<Ga. With these stacked structures, a transistor with high field-effect mobility can be manufactured. On the other hand, the atomic ratio of In to Ga in the oxide semiconductor film on the side closer to the gate electrode (channel side) is preferably In<Ga, and the atomic ratio of In to Ga in the oxide semiconductor film on the back channel side is preferably In<Ga.
By making the atomic ratio of a satisfy In≧Ga, the amount of change in threshold voltage due to deterioration over time of the transistor or due to reliability testing can be reduced.

The first oxide semiconductor film having an atomic ratio of In:Ga:Zn=1:3:2 can be formed by a sputtering method using an oxide target having an atomic ratio of In:Ga:Zn=1:3:2. The first oxide semiconductor film can be formed at room temperature using argon or a mixed gas of argon and oxygen as a sputtering gas.
The second oxide semiconductor film can be formed in a manner similar to that for the first oxide semiconductor film by using an oxide target having an atomic ratio of In:Ga:Zn=3:1:2.

Alternatively, the oxide semiconductor film may have a three-layer structure in which the first to third oxide semiconductor films contain the same elements but have different atomic ratios. A three-layer structure of the oxide semiconductor film will be described with reference to FIG.

17, a first oxide semiconductor film 299a, a second oxide semiconductor film 299b, and a third oxide semiconductor film 299c are stacked in this order from the gate insulating film 127. The first oxide _{semiconductor} film 299a and the third oxide semiconductor film 299c are formed of InM1xZnyOz ₍ x≧1, y>1, z>0, M1=Ga, Hf, or the _like ).
However, when Ga is contained in the materials constituting the first oxide semiconductor film 299a and the third oxide semiconductor film 299c _, it is inappropriate to use a material that contains a large amount of Ga, specifically, a material that can be expressed as _{InM1XZnYOZ ,} where X exceeds 10, because powder may be generated during film formation. Note that the configuration of the transistor 297 other than the first oxide semiconductor film 299a, the second oxide semiconductor film 299b, and the third oxide semiconductor film 299c is similar to that of the transistor described in the above embodiment (for example, the transistor 103 described in embodiment 1).

The material of the second oxide semiconductor film 299b _{is InM2xZnyOz} (x _≧
1, y≧x, z>0, M2=Ga, Sn, etc.) is used.

Materials of the first, second, and third oxide semiconductor films are appropriately selected so as to form a well structure in which the conduction band of the second oxide semiconductor film 299b is deeper from the vacuum level than the conduction band of the first oxide semiconductor film 299a and the conduction band of the third oxide semiconductor film 299c.

As described in Embodiment 1, silicon and carbon, which are Group 14 elements, generate electrons as carriers in the oxide semiconductor film and increase the carrier density. Therefore, when silicon or carbon is contained in the oxide semiconductor film, the oxide semiconductor film becomes n-type. Therefore, the silicon concentration and carbon concentration in each oxide semiconductor film are 3×10 ¹⁸ /c
^m3 or less, preferably 3×10 ¹⁷ /cm ³ or less.
In order to prevent a large amount of Group 14 elements from being mixed into the first oxide semiconductor film 299 a and the third oxide semiconductor film 299 b,
In other words, the first oxide semiconductor film 299 a and the third oxide semiconductor film 299 c can also be called barrier films that prevent a Group 14 element such as silicon or carbon from being mixed into the second oxide semiconductor film 299 b.

For example, the atomic ratio of the first oxide semiconductor film 299a may be In:Ga:Zn = 1:3:2, the atomic ratio of the second oxide semiconductor film 299b may be In:Ga:Zn = 3:1:2, and the atomic ratio of the third oxide semiconductor film 299c may be In:Ga:Zn = 1:1:1.
Note that the third oxide semiconductor film 299c can be formed by a sputtering method using an oxide target with an atomic ratio of In:Ga:Zn=1:1:1.

Alternatively, the first oxide semiconductor film 299 a may be formed using a compound semiconductor having an atomic ratio of In:Ga:Zn=1:3:2.
and the second oxide semiconductor film 299 b is an oxide semiconductor film having an atomic ratio of In:Ga:
A three-layer structure may be used in which an oxide semiconductor film having an atomic ratio of In:Ga:Zn=1:1:1 or In:Ga:Zn=1:3:2 is used as the first oxide semiconductor film, and a third oxide semiconductor film 299c is an oxide semiconductor film having an atomic ratio of In:Ga:Zn=1:3:2 is used as the second oxide semiconductor film.

Since the first to third oxide semiconductor films 299a to 299c contain the same constituent elements, the second oxide semiconductor film 299b has fewer defect levels (trap levels) at the interface with the first oxide semiconductor film 299a. In particular, the defect levels (trap levels) are fewer than the defect levels at the interface between the gate insulating film 127 and the first oxide semiconductor film 299a. For this reason, by stacking the oxide semiconductor films as described above, it is possible to reduce the amount of change in the threshold voltage of the transistor over time or due to a reliability test.

Furthermore, by appropriately selecting materials for the first, second, and third oxide semiconductor films to form a well structure in which the conduction band of the second oxide semiconductor film 299b is deeper than the conduction band of the first oxide semiconductor film 299a and the conduction band of the third oxide semiconductor film 299c from the vacuum level, the field-effect mobility of the transistor can be increased and the amount of change in the threshold voltage of the transistor due to aging or a reliability test can be reduced.

The first to third oxide semiconductor films 299 a to 299 c may be formed using oxide semiconductors with different crystallinity. That is, a single crystal oxide semiconductor, a polycrystalline oxide semiconductor, an amorphous oxide semiconductor, and a CAAC-OS may be combined as appropriate.
When an amorphous oxide semiconductor is used for any one of the first to third oxide semiconductor films 299a to 299c, internal stress or external stress of the oxide semiconductor film can be alleviated, and fluctuations in the electrical characteristics of the transistor can be reduced. In addition, fluctuations in the threshold voltage of the transistor due to changes over time or a reliability test can be reduced.

At least the second oxide semiconductor film 299b which can be a channel formation region is made of CAA.
The oxide semiconductor film on the back channel side, that is, the third oxide semiconductor film 299c in this embodiment, is preferably an amorphous oxide semiconductor or CAAC-OS. With such a structure, the amount of change in threshold voltage of the transistor due to aging or a reliability test can be reduced.

In the case where the transistor 297 illustrated in FIG. 17 is used as the transistor 103 in the semiconductor device of one embodiment of the present invention, the oxide semiconductor film 119 which functions as one electrode of the storage capacitor 105 is also one of the three oxide semiconductor films 299 a to 299 c.
It has a layered structure.

In this case, it can be said that a channel formation region of the transistor 297 which is a switching element of the pixel is the second oxide semiconductor film 299b.
It can be said that the first to third oxide semiconductor films 299 a to 299 c function as one electrodes of the storage capacitor 105 .

In other words, in this structure, a channel formation region of a transistor which is a switching element of a pixel is provided on a surface different from a surface on which an oxide semiconductor film which functions as one electrode of a storage capacitor is provided.

Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiments.

(Embodiment 3)
A semiconductor device (also referred to as a display device) having a display function can be manufactured using the transistor and the storage capacitor described in the above embodiment. In addition, a part or the entirety of a driver circuit including a transistor can be integrally formed over the same substrate as a pixel portion to form a system-on-panel. In this embodiment, an example of a display device using the transistor described in the above embodiment will be described with reference to the drawings.

In FIG. 18A, a sealant 905 is provided so as to surround a pixel portion 902 provided on a first substrate 901, and the pixel portion 902 is sealed with a second substrate 906.
In the above-mentioned embodiment, a signal line driver circuit 903 and a scanning line driver circuit 904 formed of a single crystal semiconductor or a polycrystalline semiconductor are mounted on a separately prepared substrate in a region different from a region surrounded by a sealant 905 on a first substrate 901.
3. Various signals and potentials given to the scanning line driver circuit 904 or the pixel portion 902 are transmitted through an FPC
(Flexible Printed Circuit) 918a and FPC 918b.

In FIG. 18B and FIG. 18C, a pixel portion 90 provided on a first substrate 901
A sealant 905 is provided so as to surround the pixel portion 902 and the scanning line driver circuit 904. A second substrate 906 is provided on the pixel portion 902 and the scanning line driver circuit 904. Therefore, the pixel portion 902 and the scanning line driver circuit 904 are not connected to the first substrate 901 and the sealant 905.
The display element is sealed by the second substrate 906.
18C, a signal line driver circuit 903 formed of a single crystal semiconductor or a polycrystalline semiconductor is mounted on a separately prepared substrate in a region different from a region surrounded by a sealing material 905 on a first substrate 901. In Fig. 18B and Fig. 18C, various signals and potentials applied to the signal line driver circuit 903, the scanning line driver circuit 904, or the pixel portion 902 are supplied from an FPC 918.

18B and 18C show an example in which the signal line driver circuit 903 is formed separately and mounted on the first substrate 901, but the present invention is not limited to this configuration. The scanning line driver circuit may be formed separately and mounted, or only a part of the signal line driver circuit or a part of the scanning line driver circuit may be formed separately and mounted.

The method of connecting the separately formed drive circuit is not particularly limited, and may be any method such as COG (
hip on glass method, wire bonding method, or TAB (Tape
FIG. 18A shows an example in which a signal line driver circuit 903 and a scanning line driver circuit 904 are mounted by a COG method.
FIG. 18B shows an example in which a signal line driver circuit 903 is mounted by the COG method.
C) is an example in which a signal line driver circuit 903 is mounted by the TAB method.

The display device includes a panel in which a display element is sealed, and a module in which an IC including a controller is mounted on the panel.

In this specification, the display device refers to an image display device or a display device.
It can also function as a light source (including lighting equipment) instead of a display device. In addition, the display device includes all of the following: a module to which a connector, such as an FPC or TCP, a module to which a printed wiring board is provided at the end of a TCP, and a module in which an IC (integrated circuit) is directly mounted on a display element by a COG method.

In addition, the pixel portion 902 and the scan line driver circuit 904 provided over the first substrate 901 each include a plurality of transistors, and the transistors described in the above embodiment modes can be used.

A liquid crystal element (also called a liquid crystal display element) or a light-emitting element (also called a light-emitting display element) can be used as a display element provided in the display device. The light-emitting element includes an element whose luminance is controlled by a current or a voltage, and specifically, an organic EL (Electroluminescent) element
Luminescence elements, inorganic EL elements, etc. Also, display media in which the contrast changes due to electrical action, such as electronic ink, can be used.
An example of a liquid crystal display device using a liquid crystal element as a display element is shown in FIG.

19 and 20 are cross-sectional views taken along dashed line X1-X2 in Fig. 18B. Note that in Fig. 19 and 20, only a part of the structure of the pixel portion is shown.

19 and 20 is a vertical electric field type liquid crystal display device. The liquid crystal display device has a connection terminal electrode 915 and a terminal electrode 916, which are electrically connected to a terminal of an FPC 918 via an anisotropic conductive agent 919.

The connection terminal electrode 915 is formed from the same conductive film as the first electrode 930, and the terminal electrode 916
is formed of the same conductive film as the source and drain electrodes of the transistors 910 and 911 .

A pixel portion 902 and a scan line driver circuit 904 provided over a first substrate 901 each include a plurality of transistors, and a transistor 910 included in the pixel portion 902 and a transistor 911 included in the scan line driver circuit 904 are illustrated as examples. An insulating film 924 corresponding to the insulating films 129, 131, and 132 described in Embodiment 1 is provided over oxide semiconductor films included in the transistors 910 and 911.
Reference numeral 23 denotes an insulating film that functions as a base film.

In this embodiment, any of the transistors described in the above embodiments can be used as the transistor 910 and the transistor 911.
A storage capacitor 926 is formed using the gate insulating film 922, the insulating film 924, and a first electrode 930. Note that the oxide semiconductor film 927 is electrically connected to a capacitance line 929 through an electrode 928 formed in an opening formed in the gate insulating film 922. The capacitance line 929 is formed from the same conductive film as the scan line including a region functioning as the gate electrodes of the transistors 910 and 911. Note that although the storage capacitor 926 has the structure described in Embodiment 1 in the drawing, a storage capacitor having the structure described in any of the other embodiments can be used as appropriate.

19A shows a structure in which a conductive film 917 is provided over an insulating film 924 in a transistor 911 included in a scan line driver circuit 904 so as to overlap with a channel formation region of the oxide semiconductor film. In FIG 19B, an insulating film 951 is provided over the insulating film 924, and a conductive film 917 is provided over the insulating film 951 so as to overlap with a channel formation region of the oxide semiconductor film.

The conductive film 917 is capable of supplying a potential and functions as a gate electrode of the transistor 911. That is, the transistor 911 is a dual-gate transistor. Note that the conductive film 917 can be formed using the same conductive film as the first electrode 930. Furthermore, the conductive film 917 can have a width in the channel length direction that is shorter than the width between the source electrode and drain electrode of the transistor 911.

The transistor 911 included in the scanning line driver circuit 904 is provided with the conductive film 917, and therefore can reduce fluctuation in the gate voltage (rising gate voltage) at which an on-current starts to flow at different drain voltages.
By providing the conductive film 917, it is possible to control a current flowing between the source electrode and the drain electrode of the transistor 911 in a region of the oxide semiconductor film on the conductive film 917 side. Therefore, a variation in electrical characteristics between a plurality of transistors included in the scan line driver circuit 904 can be reduced. In the transistor 911, by setting the potential of the conductive film 917 to the same potential as or a potential equivalent to the minimum potential of the scan line driver circuit 904, a variation in the threshold voltage of the transistor 911 can be reduced, thereby improving reliability. Note that the minimum potential of the scan line driver circuit 904 refers to the minimum potential of the scan line driver circuit 904.
For example, when the potential of the source electrode of the transistor 911 is used as a reference, the potential supplied when the scanning line driver circuit 104 is operated is the potential of the source electrode (Vss).

In the transistor 911 included in the scan line driver circuit 904, when the thickness of the insulating film 924 is thin, the electrical characteristics of the transistor 911 might change due to the influence of an electric field from the conductive film 917 applied to the oxide semiconductor film.
By providing the transistor 911, the influence of the electric field can be controlled, and the electrical characteristics of the transistor 911 can be improved.

The insulating film 951 can be formed using a material that can be used for the insulating film 924. An organic insulating film can be used as the insulating film 951. Examples of the organic insulating film include photosensitive and non-photosensitive organic resins, such as acrylic resins, benzocyclobutene resins, epoxy resins, and siloxane resins. Polyamide can be used as the organic insulating film. Note that the method for forming the organic insulating film is not particularly limited and can be appropriately selected depending on the material used. For example, spin coating, dipping, spray coating, a droplet discharge method (inkjet method), screen printing, offset printing, or the like can be used.

The conductive film 917 also has a function of blocking an external electric field. That is, the conductive film 917 also has a function of preventing the external electric field from acting on the inside (a circuit portion including a transistor) (particularly, an electrostatic blocking function against static electricity). The blocking function of the conductive film 917 can suppress fluctuations in the electrical characteristics of the transistor 911 caused by the influence of an external electric field such as static electricity, thereby improving reliability.

19 illustrates a transistor included in the scanning line driver circuit, a transistor included in the signal line driver circuit can also be a dual-gate transistor like the transistor 911. When the transistor included in the signal line driver circuit is a dual-gate transistor, the transistor has the same effect as the transistor 911.

As described above, the semiconductor device (display device) which is one embodiment of the present invention is a highly reliable semiconductor device.

Next, a structure different from that of the vertical electric field type liquid crystal display device shown in Fig. 19 will be described. Specifically, a horizontal electric field type liquid crystal display device will be described with reference to Fig. 20. Fig. 20 shows a FFS (Fringe Field Switching) mode liquid crystal display device, which is an example of the horizontal electric field type.

In the liquid crystal display device shown in Figure 20, the connection terminal electrode 915 is formed from the same material and in the same process as the first electrode 940, and the terminal electrode 916 is formed from the same material and in the same process as the source and drain electrodes of the transistors 910 and 911.

The liquid crystal element 943 includes a first electrode 940, a second electrode 941, and a liquid crystal 908, which are formed over an insulating film 924. Note that the liquid crystal element 943 can have a structure similar to that of the storage capacitor 105 described in Embodiment 1. The first electrode 940 can be formed using any of the materials shown in the first electrode 930 in FIG. 19 as appropriate. The first electrode 940 has a planar shape of
The second electrode 941 functions as a common electrode and can be formed in a manner similar to that of the oxide semiconductor film 119 described in Embodiment 1. An insulating film 924 is provided between the first electrode 940 and the second electrode 941.

The second electrode 941 is connected to a common wiring 946 via an electrode 945.
A conductive film 45 is formed from the same conductive film as the source and drain electrodes of the transistors 910 and 911. A common wiring 946 is formed from the same material and in the same process as the gate electrodes of the transistors 910 and 911. Note that although the liquid crystal element 943 is described here using the storage capacitor shown in Embodiment 1, a storage capacitor shown in any of the other embodiments can be used as appropriate.

Note that the transistor 91 included in the scanning line driver circuit 904 of the liquid crystal display device shown in FIG.
1, an insulating film 951 can be provided between the conductive film 917 and the insulating film 924 as in FIG. 19B.

Here, a structure in which a wiring including a gate electrode and a wiring including a source electrode or a drain electrode are electrically connected to each other through a conductive film in a plurality of transistors included in a semiconductor device (display device) which is one embodiment of the present invention, for example, in a scan line driver circuit 904, is described. A top view of the structure is shown in FIG 21A, and a cross-sectional view of the structure taken along dashed lines Y1-Y2 and Z1-Z2 in FIG 21A is shown in FIG 21B.

In FIG. 21A , a wiring 950 including a gate electrode of the transistor 911 and a wiring 952 including a source electrode of the transistor 911 are in contact with conductive films 958 provided in openings 954 and 956 .

In FIG. 21B, the cross-sectional structure is such that an insulating film 923 is provided over a substrate 901, a wiring 950 is provided over the insulating film 923, a gate insulating film 922 is provided over the wiring 950 and the insulating film 923, and a wiring 952 is provided over the gate insulating film 922.
An insulating film 924 is provided on the gate insulating film 922 and the wiring 952. In the region of the dashed dotted line Y1-Y2, an opening 954 is provided in the gate insulating film 922 and the insulating film 924, reaching the wiring 950, and in the region of the dashed dotted line Z1-Z2, an opening 956 is provided in the insulating film 924, reaching the wiring 952.
A conductive film 958 is provided on the insulating film 954 and the opening 956 .

From the above, the wiring 950 including the gate electrode and the wiring 95 including the source electrode or drain electrode
2 are electrically connected to each other by a conductive film 958.

The conductive film 958 can be formed by utilizing the formation process of the conductive film 917 of the transistor 911. Note that in the case where a wiring including a gate electrode and a wiring including a source electrode or a drain electrode are electrically connected to each other through a conductive film in a plurality of transistors included in the scanning line driver circuit 904, it is preferable that a conductive film not be provided in a position overlapping with a channel formation region of the transistor.

The opening 954 and the opening 956 can be formed at the same time. The details are as follows. An insulating film to be processed into the gate insulating film 922 is formed over the wiring 950, a wiring 952 is formed over the insulating film, and an insulating film to be processed into the insulating film 924 is formed over the wiring 952. Thereafter,
A mask is formed on the insulating film 924, and an opening 954 is formed by processing using the mask.
A resist mask can be used as the mask. Dry etching can be used for the processing.
By forming the wiring 950 from a metal material or the like, the etching selectivity of the wiring 950 and the gate insulating film 922 can be increased, so that the openings 954 and 956 can be formed at the same time by the dry etching.

The transistor 910 provided in the pixel portion 902 is electrically connected to the display element.

The liquid crystal element 913, which is a display element, includes a first electrode 930, a second electrode 931, and a liquid crystal layer 932.
08. Note that alignment films 932 and 933 are provided to sandwich the liquid crystal 908. The second electrode 931 is provided on the second substrate 906 side, and the first electrode 930 and the second electrode 931 overlap with each other with the liquid crystal 908 interposed therebetween. The liquid crystal element 913 can refer to the liquid crystal element 108 described in Embodiment 1. The first electrode 930 corresponds to the pixel electrode 121 described in Embodiment 1, the second electrode 931 corresponds to the counter electrode 154 described in Embodiment 1, the liquid crystal 908 corresponds to the liquid crystal 160 described in Embodiment 1, the alignment film 932 corresponds to the alignment film 158 described in Embodiment 1, and the alignment film 933 corresponds to the alignment film 156 described in Embodiment 1.

In the first electrode 930 and the second electrode 931 (also called a pixel electrode, a common electrode, a counter electrode, or the like) for applying a voltage to the display element, the direction of the extracted light, the location where the electrodes are provided,
The light transmitting or reflective property can be selected depending on the pattern structure of the electrodes.

For the first electrode 930 and the second electrode 931, materials similar to those of the pixel electrode 121 and the counter electrode 154 described in Embodiment 1 can be used as appropriate.

The spacer 935 is a columnar spacer obtained by selectively etching an insulating film, and is provided to control the distance (cell gap) between the first electrode 930 and the second electrode 931. Note that a spherical spacer may also be used.

The first substrate 901 and the second substrate 906 are fixed by a sealant 905. The sealant 905 can be made of an organic resin such as a thermosetting resin or a photocurable resin.
The sealant 905 is in contact with the insulating film 924 .

In addition, in a semiconductor device (display device) according to one embodiment of the present invention, optical members (optical substrates) such as a light-shielding film (black matrix), a polarizing member, a retardation member, and an antireflection member are appropriately provided. For example, circular polarization using a polarizing substrate and a retardation substrate may be used. In addition, a backlight, a sidelight, or the like may be used as a light source.

In addition, since a transistor is easily damaged by static electricity, etc., it is preferable to provide a protection circuit for protecting the driver circuit. The protection circuit is preferably configured using a nonlinear element.

FIG. 22 shows an example in which a common connection portion (pad portion) for electrically connecting to a second electrode 931 provided on a substrate 906 is formed over a substrate 901 in the display device shown in FIGS. 18 and 19.

The common connection portion is disposed at a position overlapping with a sealant 925 for bonding the substrate 901 and the substrate 906, and is electrically connected to the second electrode 931 via conductive particles contained in the sealant 925. Alternatively, the common connection portion may be provided in a location not overlapping with the sealant 925 (excluding the pixel portion), and a paste containing conductive particles may be provided separately from the sealant 925 so as to overlap with the common connection portion, and electrically connected to the second electrode 931.

FIG. 22A is a cross-sectional view of the common connection portion, and corresponds to IJ in the top view shown in FIG. 22B.

The common potential line 975 is provided on the gate insulating film 922 and is connected to the transistor 9 shown in FIG.
The electrode is made of the same material and in the same process as the source electrode 971 or the drain electrode 973 of FIG.

The common potential line 975 is covered with an insulating film 924.
5. These openings are formed in the same process as contact holes that connect one of a source electrode 971 or a drain electrode 973 of the transistor 910 to the first electrode 930.

In addition, the common potential line 975 and the common electrode 977 are connected at the opening.
is provided on an insulating film 924 and is manufactured from the same material and in the same process as the connection terminal electrode 915 and the first electrode 930 of the pixel portion.

In this manner, the common connection portion can be manufactured in the same manufacturing process as the switching element of the pixel portion 902 .

The common electrode 977 is an electrode that is in contact with the conductive particles contained in the sealing material, and is disposed on the substrate 906.
An electrical connection is made with the second electrode 931 .

As shown in FIG. 22C, a common potential line 985 may be formed using the same material and in the same process as the gate electrode of a transistor 910 .

22C , a common potential line 985 is provided under the gate insulating film 922 and the insulating film 924, and the gate insulating film 922 and the insulating film 924 have a plurality of openings at positions overlapping with the common potential line 985. The openings are formed by etching the insulating film 924 in the same process as the contact holes connecting one of the source electrode 971 or the drain electrode 973 of the transistor 910 to the first electrode 930, and then selectively etching the gate insulating film 922.

In addition, the common potential line 985 and the common electrode 987 are connected at the opening.
is provided on an insulating film 924 and is manufactured from the same material and in the same process as the connection terminal electrode 915 and the first electrode 930 of the pixel portion.

As described above, by using an oxide semiconductor film formed in the same formation process as an oxide semiconductor film included in a transistor as one electrode of a storage capacitor, a semiconductor device having a storage capacitor with a large charge capacity while increasing the aperture ratio can be manufactured. For example, in the semiconductor device of this embodiment, when the pixel density is 300 ppi or more, the pixel aperture ratio can be 50% or more, further the pixel aperture ratio can be 55% or more, and further the pixel aperture ratio can be 60% or more. Furthermore, by increasing the aperture ratio, a semiconductor device with excellent display quality can be obtained.

Furthermore, oxygen vacancies are reduced in the oxide semiconductor film included in the transistor, and impurities such as hydrogen and nitrogen are reduced; therefore, the semiconductor device which is one embodiment of the present invention has favorable electrical characteristics.

Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiments.

(Embodiment 4)
The semiconductor device according to one embodiment of the present invention can be applied to various electronic devices (including game machines). Examples of the electronic devices include television sets (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras,
Digital photo frames, mobile phones, portable game consoles, personal digital assistants, audio playback devices,
Examples of such electronic devices include gaming machines (pachinko machines, slot machines, etc.) and game cabinets. An example of such electronic devices is shown in FIG.

23A shows a table 9000 having a display unit. In the table 9000, a display unit 9003 is incorporated in a housing 9001, and an image can be displayed on the display unit 9003. Note that the housing 9001 is supported by four legs 9002. The housing 9001 also has a power cord 9005 for supplying power.

The semiconductor device described in any of the above embodiment modes can be used for the display portion 9003. Therefore, the display quality of the display portion 9003 can be improved.

The display unit 9003 has a touch input function.
By touching the display buttons 9004 displayed on the display portion 9003 with a finger or the like, the screen can be operated or information can be input, and the display portion 9003 may be a control device that enables communication with or control of other home appliances, thereby controlling the other home appliances through screen operations. For example, if a semiconductor device having an image sensor function is used, the display portion 9003 can have a touch input function.

In addition, the screen of the display portion 9003 can be set upright on the floor by using a hinge provided on the housing 9001, and the device can be used as a television device.
When a large-screen television set is installed, the free space becomes narrow, but if the display unit is built into the table, the space in the room can be used effectively.

FIG. 23B shows a television set 9100.
In this embodiment, a display portion 9103 is incorporated in a housing 9101, and an image can be displayed on the display portion 9103. Note that in this embodiment, the housing 9101 is supported by a stand 9105.

The television set 9100 can be operated using an operation switch provided on the housing 9101 or a separate remote control 9110. Using operation keys 9109 provided on the remote control 9110, a channel or a volume can be controlled, and an image displayed on the display portion 9103 can be operated. The remote control 9110 may be provided with a display portion 9107 that displays information output from the remote control 9110.

A television set 9100 shown in FIG. 23B includes a receiver, a modem, and the like.
The television device 9100 can receive general television broadcasts using a receiver.
Furthermore, by connecting to a wired or wireless communication network via a modem, it is possible to carry out one-way (from sender to receiver) or two-way (between sender and receiver, or between receivers themselves) information communication.

The semiconductor device described in any of the above embodiment modes can be used for the display portions 9103 and 9107. Therefore, the display quality of the television set can be improved.

FIG. 23C shows a computer 9200, which includes a main body 9201, a housing 9202, a display unit 9
203, keyboard 9204, external connection port 9205, pointing device 920
6, etc.

The semiconductor device described in any of the above embodiments can be used for the display portion 9203. Therefore, the display quality of the computer 9200 can be improved.

The display unit 9003 has a touch input function.
The display portion 9003 may be a control device that allows the user to operate the screen or input information by touching a display button displayed on the display portion 9003 with a finger or the like, and that allows communication with or control of other home appliances, thereby controlling the other home appliances by operating the screen. For example, if a semiconductor device having an image sensor function is used, the display portion 9003 can have a touch input function.

In addition, the screen of the display portion 9003 can be set upright on the floor by using a hinge provided on the housing 9001, and the device can be used as a television device.
When a large-screen television set is installed, the free space becomes narrow, but if the display unit is built into the table, the space in the room can be used effectively.

24(A) and 24(B) show a tablet terminal that can be folded in two.
) is in an open state, and the tablet terminal has a housing 9630, a display portion 9631a, a display portion 9631b, a display mode changeover switch 9034, a power switch 9035, a power saving mode changeover switch 9036, a fastener 9033, and an operation switch 9038.

The semiconductor device described in any of the above embodiments includes a display portion 9631a and a display portion 9631b.
Therefore, the display quality of the tablet terminal can be improved.

A part of the display unit 9631a can be a touch panel area 9632a, and data can be input by touching the displayed operation keys 9638.
In the example of the display unit 96, half of the display area has a display function and the other half has a touch panel function, but the display unit 96 is not limited to this configuration.
The entire area of the display unit 931a may have a touch panel function.
The entire surface of the display portion 9631a can be used as a touch panel by displaying keyboard buttons, and the display portion 9631b can be used as a display screen.

Similarly to the display portion 9631a, part of the display portion 9631b can be used as a touch panel area 9632b. When a position on the touch panel where a keyboard display switch button 9639 is displayed is touched with a finger, a stylus, or the like, keyboard buttons can be displayed on the display portion 9631b.

In addition, touch input can be made simultaneously to touch panel area 9632a and touch panel area 9632b.

Furthermore, the display mode changeover switch 9034 can change the display orientation, such as portrait or landscape, and can select black and white or color display. The power saving mode changeover switch 9036 can optimize the display brightness according to the amount of external light during use detected by an optical sensor built into the tablet terminal. The tablet terminal may be equipped with not only an optical sensor, but also other detection devices such as a gyro, an acceleration sensor, or other sensors that detect tilt.

24A shows an example in which the display areas of the display portions 9631b and 9631a are the same, but this is not particularly limited, and the sizes of the display portions may be different from each other, and the display qualities may also be different. For example, one display panel may be capable of displaying images with higher resolution than the other.

FIG. 24B shows the tablet terminal in a closed state. The tablet terminal includes a housing 9630 and a solar cell 9
24B, the charge/discharge control circuit 96
As an example of the power supply 34, a configuration having a battery 9635 and a DC-DC converter 9636 is shown.

Note that the tablet terminal can be folded in half, and therefore the housing 9630 can be kept closed when not in use.
This makes it possible to provide a tablet device that is highly durable and reliable even when used for a long period of time.

In addition, the tablet terminals shown in Figures 24 (A) and 24 (B) can have a function to display various information (still images, videos, text images, etc.), a function to display a calendar, date or time on the display unit, a touch input function to perform touch input operations or edit the information displayed on the display unit, and a function to control processing using various software (programs), etc.

A solar cell 9633 attached to the surface of the tablet terminal can supply power to a touch panel, a display unit, a video signal processor, or the like.
This is preferable because the battery 9635 can be provided on one or both sides of the housing 9630 and can efficiently charge the battery 9635. Note that using a lithium ion battery as the battery 9635 has an advantage that it can be made smaller.

The configuration and operation of the charge/discharge control circuit 9634 shown in FIG.
FIG. 24C shows a block diagram of the solar cell 9633 and the battery 9
635, DC-DC converter 9636, converter 9637, switches SW1 to SW3
, a display unit 9631, a battery 9635, a DCDC converter 963
6, a converter 9637, and switches SW1 to SW3 correspond to the charge/discharge control circuit 9634 shown in FIG.

First, an example of operation in the case where power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell is converted into a voltage for charging the battery 9635.
The voltage is increased or decreased by the CDC converter 9636. When power from the solar cell 9633 is used for the operation of the display portion 9631, the switch SW1 is turned on, and the converter 9637 increases or decreases the voltage to a voltage required for the display portion 9631. When no display is to be performed on the display portion 9631, SW1 is turned off and SW2 is turned on to charge the battery 9635.

Although the solar cell 9633 is shown as an example of a power generating means, it is not particularly limited, and may be configured to charge the battery 9635 using other power generating means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a non-contact power transmission module that transmits and receives power wirelessly (non-contact) for charging, or a combination with other charging means may be used.

Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiments.

Claims (4)

a first pixel including a first transistor, a first pixel electrode electrically connected to the first transistor, and a first capacitor;
a second pixel including a second transistor, a second pixel electrode electrically connected to the second transistor, and a second capacitor;
A third conductive film;
having
the first transistor includes a first conductive film having a region functioning as a gate electrode and a first oxide semiconductor film having a region overlapping with the first conductive film;
the first capacitor includes a second oxide semiconductor film;
the second oxide semiconductor film has a light-transmitting property and includes a region that functions as one electrode of the first capacitor;
the first pixel electrode has a light-transmitting property and has a region that functions as the other electrode of the first capacitor element;
the second transistor has a region functioning as a gate electrode, and includes a second conductive film formed in the same layer as the first conductive film, and a third oxide semiconductor film having a region overlapping with the second conductive film;
the second capacitor includes a fourth oxide semiconductor film;
the fourth oxide semiconductor film has a light-transmitting property and has a region which functions as one electrode of the second capacitor;
the second pixel electrode has a light-transmitting property and has a region that functions as the other electrode of the second capacitor element;
the second oxide semiconductor film is electrically connected to the fourth oxide semiconductor film via the third conductive film;
In a plan view, the first conductive film has a region extending along a first direction,
In a plan view, the third conductive film has a region extending along a second direction intersecting the first direction,
In a plan view, the second oxide semiconductor film has a first region protruding along the second direction,
the second oxide semiconductor film is electrically connected to the third conductive film having a second width larger than the first width through the first region having a first width;
In a plan view, the fourth oxide semiconductor film has a second region protruding along the second direction,
the fourth oxide semiconductor film is electrically connected to the third conductive film through the second region having a third width smaller than the second width . a first pixel including a first transistor, a first pixel electrode electrically connected to the first transistor, and a first capacitor;
a second pixel including a second transistor, a second pixel electrode electrically connected to the second transistor, and a second capacitor;
A third conductive film;
having
the first transistor includes a first conductive film having a region functioning as a gate electrode and a first oxide semiconductor film having a region overlapping with the first conductive film;
the first capacitor includes a second oxide semiconductor film;
the second oxide semiconductor film has a light-transmitting property and includes a region that functions as one electrode of the first capacitor;
the first pixel electrode has a light-transmitting property and has a region that functions as the other electrode of the first capacitor element;
the second transistor has a region functioning as a gate electrode, and includes a second conductive film formed in the same layer as the first conductive film, and a third oxide semiconductor film having a region overlapping with the second conductive film;
the second capacitor includes a fourth oxide semiconductor film;
the fourth oxide semiconductor film has a light-transmitting property and has a region which functions as one electrode of the second capacitor;
the second pixel electrode has a light-transmitting property and has a region that functions as the other electrode of the second capacitor element;
the second oxide semiconductor film is electrically connected to the fourth oxide semiconductor film via the third conductive film;
In a plan view, the first conductive film has a region extending along a first direction,
In a plan view, the third conductive film has a region extending along a second direction intersecting the first direction,
the second oxide semiconductor film has a first region extending along the second direction in a plan view;
the second oxide semiconductor film is electrically connected to the third conductive film having a second width larger than the first width through the first region having a first width;
the fourth oxide semiconductor film has a second region extending along the second direction in a plan view;
the fourth oxide semiconductor film is electrically connected to the third conductive film through the second region having a third width smaller than the second width . In claim 1 or 2,
The display device, wherein the third conductive film has a region where it intersects with the first conductive film. In any one of claims 1 to 3,
The display device, wherein the first region and the second region function as a capacitance line.

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