# Patent

## Title
Semiconductor device

## Abstract

An oxide semiconductor transistor comprising an oxide semiconductor layer with high conductivity is provided. A semiconductor device including an oxide semiconductor layer comprising an oxide containing indium, gallium, and zinc (IGZO) and a particle of indium oxide; a gate electrode overlapping with a channel formation region in the oxide semiconductor layer with a gate insulating film interposed therebetween; and a source electrode and a drain electrode overlapping with a source region and a drain region in the oxide semiconductor layer. The semiconductor device may be a top-gate oxide semiconductor transistor or a bottom-gate oxide semiconductor transistor. The oxide semiconductor layer may be formed over or below the source electrode and the drain electrode.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
One embodiment of the disclosed invention relates to a semiconductor device.
2. Description of the Related Art
In recent years, a technique in which transistors are manufactured using an oxide semiconductor and applied to electronic devices or optical devices has attracted attention. For example, Patent Document 1 and Patent Document 2 disclose a technique in which a transistor is formed using an oxide containing indium (In), gallium (Ga), and zinc (Zn) (hereinafter called “IGZO”) as an oxide semiconductor to manufacture a display device using the transistor.
REFERENCE
Patent Document
[Patent Document 1] Japanese Published Patent Application No. 2007-123861
[Patent Document 2] Japanese Published Patent Application No. 2007-096055
SUMMARY OF THE INVENTION
IGZO has low conductivity. An oxide semiconductor transistor in which IGZO is used for an active layer might have a low on-state current, for example.
In view of the above, an object of one embodiment of the disclosed invention is to provide an oxide semiconductor transistor including an oxide semiconductor layer with high conductivity.
One embodiment of the disclosed invention relates to a semiconductor device including an oxide semiconductor layer comprising an oxide containing indium, gallium, and zinc (IGZO) and a particle of indium oxide; a gate electrode overlapping with a channel formation region in the oxide semiconductor layer with a gate insulating film interposed therebetween; and a source electrode and a drain electrode overlapping with a source region and a drain region in the oxide semiconductor layer.
According to one embodiment of the disclosed invention, an oxide semiconductor layer comprises IGZO in which a crystal of indium oxide (In2O3) formed by bonding indium and oxygen contained in IGZO together exists as a particle.
Indium oxide whose energy gap is 2.8 eV is a semiconductor which is close to an insulator in characteristics. When indium and oxygen included in IGZO form a particle of indium oxide which is close to an insulator in characteristics, electric charge in IGZO is polarized. That is, in IGZO, the particle of indium oxide has characteristics close to those of an insulator, while a portion from which oxygen and indium are extracted to form the particle of indium oxide has higher conductivity than the other portions. In addition, particles of indium oxide are dispersed in the oxide semiconductor layer; for this reason, the movement of carriers is not interrupted. Thus, the oxide semiconductor layer comprising IGZO in which the particle of indium oxide exists has high conductivity.
By using the oxide semiconductor layer with high conductivity as an oxide semiconductor layer of an oxide semiconductor transistor, the carrier mobility increases and the on-state current of the oxide semiconductor transistor increases.
One embodiment of the disclosed invention relates to a semiconductor device including: a gate electrode; a gate insulating film covering the gate electrode; an oxide semiconductor layer comprising an oxide containing indium, gallium, and zinc and a particle of indium oxide, and overlapping with the gate electrode with the gate insulating film interposed therebetween; and a source electrode and a drain electrode over a source region and a drain region in the oxide semiconductor layer.
One embodiment of the disclosed invention relates to a semiconductor device including: a gate electrode; a gate insulating film covering the gate electrode; a source electrode and a drain electrode over the gate insulating film; and an oxide semiconductor layer comprising an oxide containing indium, gallium, and zinc and a particle of indium oxide. The oxide semiconductor layer is located over the gate electrode with the gate insulating film interposed therebetween, and is located over the source electrode and the drain electrode.
One embodiment of the disclosed invention relates to a semiconductor device including: an oxide semiconductor layer comprising an oxide containing indium, gallium, and zinc and a particle of indium oxide; a source electrode and a drain electrode over a source region and a drain region in the oxide semiconductor layer; a gate insulating film covering the oxide semiconductor layer, the source electrode and the drain electrode; and a gate electrode over a channel formation region in the oxide semiconductor layer with the gate insulating film interposed therebetween.
One embodiment of the disclosed invention relates to a semiconductor device including: a source electrode and a drain electrode; an oxide semiconductor layer over the source electrode and the drain electrode, which comprises an oxide containing indium, gallium, and zinc and a particle of indium oxide, and includes a source region and a drain region overlapping with the source electrode and the drain electrode; a gate insulating film covering the oxide semiconductor layer; and a gate electrode over a channel formation region in the oxide semiconductor layer with the gate insulating film interposed therebetween.
According to one embodiment of the disclosed invention, an oxide semiconductor transistor including an oxide semiconductor layer with high conductivity can be provided.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are cross-sectional views of semiconductor devices;
FIGS. 2A and 2B are cross-sectional views of semiconductor devices;
FIG. 3 is a TEM photograph of a cross section of an oxide semiconductor layer;
FIG. 4 shows a result of TEM-FFT analysis of an oxide semiconductor layer;
FIG. 5 shows a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor;
FIG. 6 shows a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor;
FIG. 7 shows a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor;
FIG. 8 shows a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor;
FIG. 9 shows a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor;
FIG. 10 shows a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor;
FIG. 11 shows a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor; and
FIG. 12 shows a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor.



DETAILED DESCRIPTION OF THE INVENTION
Embodiment of the invention disclosed in this specification will be hereinafter described with reference to the accompanying drawings. Note that the invention disclosed in this specification can be carried out in a variety of different modes, and it is easily understood by those skilled in the art that the modes and details of the invention disclosed in this specification can be changed in various ways without departing from the spirit and scope thereof. Therefore, the present invention is not construed as being limited to description of the embodiment. Note that, in the drawings hereinafter shown, the same portions or portions having similar functions are denoted by the same reference numerals, and repeated description thereof will be omitted.
Note that in the invention disclosed in this specification, a semiconductor device refers to an element or a device which functions by utilizing a semiconductor and includes, in its category, an electric device including an electronic circuit, a display device, a light-emitting device, and the like and an electronic appliance on which the electric device is mounted.
Note that the position, size, range, or the like of each structure shown in the drawings and the like is not accurately represented in some cases for easy understanding. Therefore, the disclosed invention is not necessarily limited to the position, size, range, or the like as disclosed in the drawings and the like.
In this specification and the like, ordinal numbers such as “first”, “second”, and “third” are used in order to avoid confusion among components, and the terms do not mean limitation of the number of components.
FIGS. 1A and 1B and FIGS. 2A and 2B illustrate structures of oxide semiconductor transistors according to this embodiment.
An oxide semiconductor transistor 101 illustrated in FIG. 1A includes a base insulating film 102 over a substrate 100; a gate electrode 103 over the base insulating film 102; a gate insulating film 104 covering the base insulating film 102 and the gate electrode 103; an oxide semiconductor layer 105 overlapping with the gate electrode 103 with the gate insulating film 104 interposed therebetween and functioning as an active layer; and an electrode 106a and an electrode 106b over a source region and a drain region in the oxide semiconductor layer 105 and functioning as a source electrode and a drain electrode.
The oxide semiconductor transistor 101 illustrated in FIG. 1A is a bottom-gate transistor in which the gate electrode 103 is formed below the oxide semiconductor layer 105, and is also a top-contact transistor in which the electrode 106a and the electrode 106b functioning as the source electrode and the drain electrode are formed over the oxide semiconductor layer 105.
In the oxide semiconductor transistor 101 illustrated in FIG. 1A, a region of the oxide semiconductor layer 105, which is over the gate electrode 103, that is, a channel formation region, has a smaller thickness than the other regions thereof due to the influence of etching and the like. The transistor whose channel formation region is thin is referred to as a channel-etch transistor. The oxide semiconductor transistor 101 illustrated in FIG. 1A may be not only the channel-etch transistor, but also a channel-protective transistor which has a protective insulating film over a channel formation region.
An oxide semiconductor transistor 111 illustrated in FIG. 1B includes a base insulating film 112 over a substrate 110; a gate electrode 113 over the base insulating film 112; a gate insulating film 114 covering the base insulating film 112 and the gate electrode 113; an electrode 116a and an electrode 116b over the gate insulating film 114 and functioning as a source electrode and a drain electrode; and an oxide semiconductor layer 115. The oxide semiconductor layer 115 functioning as an active layer is located over the gate electrode 113 with the gate insulating film 114 interposed therebetween, and is located over the electrode 116a and the electrode 116b functioning as the source electrode and the drain electrode.
In FIG. 1B, the electrode 116a and the electrode 116b functioning as a source electrode and a drain electrode do not overlap with the gate electrode 113. If needed, portions of the electrode 116a and the electrode 116b may overlap with the gate electrode 113 with the gate insulating film 114 interposed therebetween.
The oxide semiconductor transistor 111 illustrated in FIG. 1B is a bottom-gate transistor in which the gate electrode 113 is formed below the oxide semiconductor layer 115, and is also a bottom-contact transistor in which the electrode 116a and the electrode 116b functioning as the source electrode and the drain electrode are formed below portions of the oxide semiconductor layer 115.
An oxide semiconductor transistor 201 illustrated in FIG. 2A includes a base insulating film 202 over a substrate 200; an oxide semiconductor layer 203 over the base insulating film 202 and functioning as an active layer; an electrode 204a and an electrode 204b over the oxide semiconductor layer 203 and functioning as a source electrode and a drain electrode; a gate insulating film 206 over the oxide semiconductor layer 203, the electrode 204a, and the electrode 204b; and a gate electrode 207 overlapping with a channel formation region 209 in the oxide semiconductor layer 203 with the gate insulating film 206 interposed therebetween.
The oxide semiconductor transistor 201 illustrated in FIG. 2A is a top-gate transistor in which the gate electrode 207 is formed over the oxide semiconductor layer 203, and is also a top-contact transistor in which the electrode 204a and the electrode 204b functioning as the source electrode and the drain electrode are formed over the oxide semiconductor layer 203.
A region 208a and a region 208b in the oxide semiconductor layer 203, which overlap with the electrode 204a and the electrode 204b, function as a source region and a drain region.
In addition, a region 211a is located between the channel formation region 209 and the region 208a, and a region 211b is located between the channel formation region 209 and the region 208b. The region 211a and the region 211b function as offset regions.
An oxide semiconductor transistor 221 illustrated in FIG. 2B includes a base insulating film 222 over a substrate 220; an electrode 224a and an electrode 224b over the base insulating film 222 and functioning as a source electrode and a drain electrode; an oxide semiconductor layer 223 over the electrode 224a and the electrode 224b, which includes a source region and a drain region overlapping with the electrode 224a and the electrode 224b, and which functions as an active layer; a gate insulating film 226 over the oxide semiconductor layer 223, the electrode 224a and the electrode 224b; and a gate electrode 227 overlapping with a channel formation region 229 in the oxide semiconductor layer 223 with the gate insulating film 226 interposed therebetween.
In FIG. 2B, the electrode 224a and the electrode 224b functioning as a source electrode and a drain electrode do not overlap with the gate electrode 227. If needed, portions of the electrode 224a and the electrode 224b may overlap with the gate electrode 227 with the oxide semiconductor layer 223 and the gate insulating film 226 interposed therebetween.
The oxide semiconductor transistor 221 illustrated in FIG. 2B is a top-gate transistor in which the gate electrode 227 is formed over the oxide semiconductor layer 223, and is also a bottom-contact transistor in which the electrode 224a and the electrode 224b functioning as the source electrode and the drain electrode are formed below the oxide semiconductor layer 223.
A region 228a and a region 228b in the oxide semiconductor layer 223, which overlap with the electrode 224a and the electrode 224b, function as a source region and a drain region.
In addition, a region 231a is located between the channel formation region 229 and the region 228a, and a region 231b is located between the channel formation region 229 and the region 228b. The region 231a and the region 231b function as offset regions.
The oxide semiconductor layer 105 in the oxide semiconductor transistor 101 illustrated in FIG. 1A, the oxide semiconductor layer 115 in the oxide semiconductor transistor 111 illustrated in FIG. 1B, the oxide semiconductor layer 203 in the oxide semiconductor transistor 201 illustrated in FIG. 2A, and the oxide semiconductor layer 223 in the oxide semiconductor transistor 221 illustrated in FIG. 2B are oxide semiconductor layers comprising IGZO and a particle of indium oxide.
As described above, the oxide semiconductor layer comprising IGZO and a particle of indium oxide is an oxide semiconductor layer comprising IGZO in which a crystal of indium oxide (In2O3) formed by bonding indium and oxygen included in IGZO together exists as a particle.
Indium oxide whose energy gap is 2.8 eV is a semiconductor which is close to an insulator in characteristics. When indium and oxygen contained in IGZO form a particle of indium oxide which is close to an insulator in characteristics, the distribution of an electric charge in IGZO becomes uneven. That is, in IGZO, the particle of indium oxide has characteristics close to those of an insulator, while a portion from which oxygen and indium are extracted to form the particle of indium oxide has higher conductivity than the other portions. In addition, the particle of indium oxide is dispersed in the oxide semiconductor layer; for this reason, the movement of carriers is not interrupted. Thus, the oxide semiconductor layer comprising IGZO in which the particle of indium oxide exists has high conductivity.
Therefore, an oxide semiconductor transistor including the oxide semiconductor layer comprising IGZO and a particle of indium oxide has high conductivity. The oxide semiconductor transistor with high conductivity has an advantage of having a high on-state current, for example.
FIG. 3 is a TEM photograph of a cross section of an oxide semiconductor layer comprising IGZO and a particle used in this embodiment.
The oxide semiconductor layer comprising IGZO and a particle shown in FIG. 3 was formed at a substrate temperature of 250° C. by a sputtering method.
Upon analyzing the particle with a TEM-FFT (Transmission Electron Microscopy-Fast Fourier Transform), it turns out that the particle is indium oxide. The following shows that the particle is indium oxide.
The TEM-FFT can Fourier transform the pattern of an obtained lattice image and thereby analyze the spot position of the pattern, and can analyze an interplanar spacing in crystal and a crystal plane orientation.
In this embodiment, a particle in an oxide semiconductor layer was analyzed with the TEM-FFT, and an interplanar spacing in crystal was obtained. The result was such that the d-value of the particle in the oxide semiconductor layer was A: 0.501 nm, B: 0.265 nm, and C: 0.302 nm (see FIG. 4). Since the d-value of indium oxide (In2O3) is A: 0.506 nm, B: 0.270 nm, and C: 0.320 nm, it is proved that a component of the particle is indium oxide (In2O3).
FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and FIG. 12 each show a relation between a drain current (Id) and a gate voltage (Vg) of an oxide semiconductor transistor using an oxide semiconductor layer of this embodiment.
The oxide semiconductor transistors used in the measurement of FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and FIG. 12 are the bottom-gate top-contact oxide semiconductor transistors 101 shown in FIG. 1A. In the oxide semiconductor transistor 101 used in the measurement of FIG. 5, the base insulating film 102 is a stacked-layer film in which a silicon oxynitride film with a film thickness of 150 nm is stacked over a silicon nitride film with a film thickness of 100 nm. The gate electrode 103 is a tungsten (W) film with a film thickness of 100 nm. The gate insulating film 104 is a silicon nitride film containing oxygen with a film thickness of 100 nm.
The oxide semiconductor layers 105 were formed to have a film thickness of 35 nm under the following conditions: the film formation pressure was 0.3 Pa, the film formation power was 9 kW (AC), the flow rate ratio of oxygen (O2) to argon was set to 50%, and the substrate temperature was 150° C. After the film formation was performed under above conditions, the oxide semiconductor layers of FIG. 5, FIG. 7, FIG. 9, and FIG. 11 were baked at 350° C. for one hour in a nitrogen atmosphere, and then, were baked at 350° C. for one hour in an atmosphere containing nitrogen and oxygen, and the oxide semiconductor layers of FIG. 6, FIG. 8, FIG. 10, and FIG. 12 were baked at 450° C. for one hour in a nitrogen atmosphere, and then, were baked at 450° C. for one hour in an atmosphere containing nitrogen and oxygen. These oxide semiconductor layers were used as the oxide semiconductor layers 105 in the respective measurements.
An electrode 106a and an electrode 106b were formed using a stacked-layer film of a titanium film with a film thickness of 100 nm, an aluminum film with a film thickness of 400 nm, and a titanium film with a film thickness of 100 nm.
The oxide semiconductor transistors were made to have a channel length L of 3 μm and a channel width W of 3 μm in FIG. 5 and FIG. 6, to have a channel length L of 3 μm and a channel width W of 50 μm in FIG. 7 and FIG. 8, to have a channel length L of 6 μm and a channel width W of 50 μm in FIG. 9 and FIG. 10, and to have a channel length L of 10 μm and a channel width W of 50 μm in FIG. 11 and FIG. 12.
As an interlayer insulating film (not illustrated), a silicon oxide film of 400 nm in thickness and a photosensitive acrylic resin film of 1500 nm in thickness were formed to cover the oxide semiconductor transistor 101.
Finally, baking was performed at 250° C. for one hour in a nitrogen atmosphere.
As shown in FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and FIG. 12, while there are some variations in the on-state current, the oxide semiconductor transistors of FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and FIG. 12 each have a high on-state current. According to this embodiment, a favorable oxide semiconductor transistor whose on-state current is high can be obtained.
This application is based on Japanese Patent Application serial no. 2011-178799 filed with Japan Patent Office on Aug. 18, 2011, the entire contents of which are hereby incorporated by reference.

## Claims

1. A semiconductor device comprising:
a gate electrode;
a gate insulating film covering the gate electrode;
an oxide semiconductor layer comprising an oxide containing indium, gallium, and zinc and including a particle of indium oxide represented by In2O3, wherein the oxide semiconductor layer overlaps with the gate electrode with the gate insulating film interposed therebetween; and
a source electrode and a drain electrode over a source region and a drain region in the oxide semiconductor layer,
wherein the particle has a wedge shape.

2. The semiconductor device according to claim 1, wherein the oxide semiconductor layer is included in a channel-etch transistor.

3. The semiconductor device according to claim 1, further comprising a substrate and a base insulating film below the gate electrode.

4. The semiconductor device according to claim 1, wherein a tip of the wedge shape is in a direction apart from a top surface of the oxide semiconductor layer.

5. A semiconductor device comprising:
a gate electrode over a substrate;
an oxide semiconductor layer including a channel formation region, a source region, and a drain region, the channel formation region being adjacent to the gate electrode with a gate insulating film interposed therebetween; and
a source electrode and a drain electrode being in contact with the source region and the drain region,
wherein the oxide semiconductor layer comprises an oxide containing indium, gallium, and zinc and includes a particle of indium oxide represented by In2O3,
wherein the oxide semiconductor layer includes:
a first portion containing indium, gallium, zinc and oxygen; and
a second portion,

wherein a density of indium in the second portion is lower than a density of indium in the first portion,
wherein a density of oxygen in the second portion is lower than a density of oxygen in the first portion,
wherein the second portion has higher conductivity than other portions of the oxide semiconductor layer, and
wherein the particle has a wedge shape.

6. The semiconductor device according to claim 5, further comprising a base insulating film on the substrate.

7. The semiconductor device according to claim 5, wherein the oxide semiconductor layer covers the gate electrode.

8. The semiconductor device according to claim 5, wherein the source electrode and the drain electrode are provided on the source region and the drain region, respectively.

9. The semiconductor device according to claim 5, wherein a tip of the wedge shape is in a direction apart from a top surface of the oxide semiconductor layer.

10. A semiconductor device comprising:
a gate electrode over a substrate;
an oxide semiconductor layer including a channel formation region, a source region, and a drain region, the channel formation region being adjacent to the gate electrode with a gate insulating film interposed therebetween; and
a source electrode and a drain electrode being in electrical contact with the source region and the drain region,
wherein the oxide semiconductor layer comprises an oxide containing indium, gallium, and zinc and includes a particle of indium oxide,
wherein the oxide semiconductor layer includes:
a first portion containing indium, gallium, zinc and oxygen; and
a second portion,

wherein a density of indium in the second portion is lower than a density of indium in the first portion,
wherein a density of oxygen in the second portion is lower than a density of oxygen in the first portion,
wherein the second portion has higher conductivity than other portions of the oxide semiconductor layer, and
wherein the particle has a wedge shape.

11. The semiconductor device according to claim 10, further comprising a base insulating film on the substrate.

12. The semiconductor device according to claim 10, wherein the oxide semiconductor layer covers the gate electrode.

13. The semiconductor device according to claim 10, wherein the source electrode and the drain electrode are provided on the source region and the drain region, respectively.

14. The semiconductor device according to claim 10, wherein the indium oxide is represented by In2O3.

15. The semiconductor device according to claim 10, wherein a tip of the wedge shape is in a direction apart from a top surface of the oxide semiconductor layer.