Patent Application
20170162713
The present invention relates to a thin film transistor (TFT), a method for manufacturing the thin film transistor, and an organic EL display device, and in particular to an oxide semiconductor thin film transistor having an oxide semiconductor layer in an active layer, a method for manufacturing the oxide semiconductor thin film transistor, and an organic EL display device including an oxide semiconductor thin film transistor.
Active matrix display devices such as liquid crystal display devices and organic electroluminescent (EL) display devices use TFTs as switching elements or driver elements.
In recent years, active development has been conducted on, as next-generation TFTs, oxide semiconductor TFTs which use an oxide semiconductor such as InGaZnOx (IGZO) for channel layers. For example, Patent Literature (PTL) 1 discloses an oxide semiconductor TFT having an oxide semiconductor layer as a channel layer.
The electrical characteristics of oxide semiconductor TFTs are susceptible to oxygen or hydrogen (see NPL 1, for example). For this reason, it has been difficult to obtain oxide semiconductor TFTs having high reliability.
The present invention has been conceived to solve such a problem, and an object of the present invention is to provide a thin film transistor having high reliability, a method for manufacturing the thin film transistor, and an organic EL display device.
In order to achieve the above object, a thin film transistor according to an aspect of the present invention includes: a gate electrode; a source electrode and a drain electrode; an oxide semiconductor layer used as a channel layer; and a gate insulating layer disposed between the gate electrode and the oxide semiconductor layer, wherein metallic elements included in the oxide semiconductor layer include at least indium, and fluorine is included in a region which is an internal region in the oxide semiconductor layer and is close to the gate insulating layer.
The present invention allows a thin film transistor to be less susceptible to oxygen or hydrogen, thereby achieving the thin film transistor having high reliability and high robustness.
A thin film transistor according to an aspect of the present invention includes: a gate electrode; a source electrode and a drain electrode; an oxide semiconductor layer used as a channel layer; and a gate insulating layer disposed between the gate electrode and the oxide semiconductor layer, wherein metallic elements included in the oxide semiconductor layer include at least indium, and fluorine is included in a region which is an internal region in the oxide semiconductor layer and is close to the gate insulating layer.
According to the aspect of the present invention, fluorine is included in the region that is the internal region in the oxide semiconductor layer and is close to the gate insulating layer.
Fluorine has higher binding energy with metal than oxygen. Accordingly, including fluorine in the oxide semiconductor layer enables fluorine to eliminate dangling bonds or an unstable site caused by oxygen deficiency in the oxide semiconductor layer. In other words, including fluorine in the oxide semiconductor layer makes it possible to compensate the oxygen deficiency in the oxide semiconductor layer.
Moreover, including fluorine in the oxide semiconductor layer prevents hydrogen entering the oxide semiconductor layer from bonding with the oxide semiconductor layer. With this, it is possible to prevent hydrogen from entering the oxide semiconductor layer, thereby suppressing generation of charge carriers resulting from bonding of oxygen and hydrogen in the oxide semiconductor layer. In short, including fluorine in the oxide semiconductor layer makes it possible to improve hydrogen resistance of the oxide semiconductor layer.
Furthermore, including fluorine in the oxide semiconductor layer results in the metallic elements included in the oxide semiconductor layer being chemically bonded with fluorine, which makes it possible to stabilize a structure of the oxide semiconductor layer.
As just described, according to the aspect of the present invention, it is possible to make the oxide semiconductor layer less susceptible to damage resulting hydrogen or oxygen as well as stabilize the structure of the oxide semiconductor layer. With this, it is possible to achieve a thin film transistor having high reliability and high robustness.
Moreover, in the thin film transistor according to the aspect of the present invention, the region including fluorine in the oxide semiconductor layer may have a film thickness of at least 5 nm.
According to the aspect of the present invention, it is possible to sufficiently exert the aforementioned effects of including fluorine.
In addition, in the thin film transistor according to the aspect of the present invention, the region including fluorine in the oxide semiconductor layer may have a film thickness of at least 20 nm.
Annealing may be performed with the aim of stabilizing characteristics of the oxide semiconductor layer, but this annealing may diffuse hydrogen and hydrogen may enter the oxide semiconductor layer. In response, even if the annealing or the like diffuses hydrogen, setting the film thickness of the region including fluorine in the oxide semiconductor layer enables the region including fluorine in the oxide semiconductor layer to prevent hydrogen from entering the oxide semiconductor layer.
Moreover, in the thin film transistor according to the aspect of the present invention, a fluorine concentration of the oxide semiconductor layer may be set higher than at least a hydrogen concentration of the oxide semiconductor layer.
According to the aspect of the present invention, it is possible to sufficiently exert the aforementioned effects of including fluorine.
Moreover, in the thin film transistor according to the aspect of the present invention, the metallic elements included in the oxide semiconductor layer may further include at least one or both of gallium and zinc.
According to the aspect of the present invention, target compatibility with large mass production facilities is increased, and thus production costs can be reduced.
Moreover, in the thin film transistor according to the aspect of the present invention, the gate electrode, the gate insulating layer, and the oxide semiconductor layer may be stacked in listed order on a substrate, and the source electrode and the drain electrode may be formed above the oxide semiconductor layer.
According to the aspect of the present invention, compatibility with production line facilities (existing facilities) for amorphous silicon TFTs for use in liquid crystal displays is increased, and thus production costs can be reduced.
Moreover, the thin film transistor according to the aspect of the present invention may further include a channel protective layer formed on the oxide semiconductor layer.
According to the aspect of the present invention, it is possible to reduce process damage on a back channel side of the oxide semiconductor layer (channel layer).
Moreover, in the thin film transistor according to the aspect of the present invention, the oxide semiconductor layer, the gate insulating layer, and the gate electrode may be stacked in listed order on a substrate, the source electrode may be connected to a source region in the oxide semiconductor layer via a contact hole formed in the gate insulating layer, and the drain electrode may be connected to a drain region in the oxide semiconductor layer via a contact hole formed in the gate insulating layer.
According to the aspect of the present invention, it is possible to reduce parasitic capacitance.
Moreover, a method for manufacturing a thin film transistor according to an aspect of the present invention, the method includes: forming a gate electrode; forming a source electrode and a drain electrode; forming an oxide semiconductor layer used as a channel layer; and forming a gate insulating layer to be between the gate electrode and the oxide semiconductor layer, wherein metallic elements included in the oxide semiconductor layer include at least indium, and in the forming of the oxide semiconductor layer, the oxide semiconductor layer is formed while introducing fluorine into the oxide semiconductor layer.
According to the aspect of the present invention, it is possible to obtain a thin film transistor which is less susceptible to damage resulting from hydrogen or oxygen and includes the oxide semiconductor layer having a stable structure. Therefore, it is possible to obtain the thin film transistor having high reliability and high robustness.
Moreover, in the method according to the aspect of the present invention, in the forming of the oxide semiconductor layer, the oxide semiconductor layer may be formed to include fluorine in a region which is an internal region in the oxide semiconductor layer and is close to the gate insulating layer.
With this, hydrogen entering the oxide semiconductor layer from the gate insulating layer can be blocked with the region close to the gate insulating layer in the oxide semiconductor layer.
Moreover, in the method according to the aspect of the present invention, in the forming of the oxide semiconductor layer, the oxide semiconductor layer may be formed by sputtering using a target material including fluorine.
According to the aspect of the present invention, it is possible to deposit the oxide semiconductor layer in which fluorine is included by sputtering.
Moreover, in the method according to the aspect of the present invention, in the forming of the oxide semiconductor layer, the oxide semiconductor layer may be formed using a gas including fluorine.
According to the aspect of the present invention, providing the gas including fluorine makes it possible to deposit the oxide semiconductor layer in which fluorine is included.
Moreover, in the method according to the aspect of the present invention, the region including fluorine in the oxide semiconductor layer may have a film thickness of at least 5 nm.
According to the aspect of the present invention, it is possible to obtain the thin film transistor which is capable of sufficiently exerting the aforementioned effects of including fluorine.
Moreover, in the method according to the aspect of the present invention, the region including fluorine in the oxide semiconductor layer may have a film thickness of at least 20 nm.
According to the aspect of the present invention, even if annealing or the like diffuses hydrogen, the region including fluorine in the oxide semiconductor layer is capable of preventing hydrogen from entering the oxide semiconductor layer. In addition, setting the film thickness of the region including fluorine to be at least 20 nm makes it possible to sufficiently perform process control of the oxide semiconductor layer.
Moreover, in the method according to the aspect of the present invention, a fluorine concentration of the oxide semiconductor layer may be set higher than at least a hydrogen concentration of the oxide semiconductor layer.
According to the aspect of the present invention, it is possible to obtain the thin film transistor which is capable of sufficiently exerting the aforementioned effects of including fluorine.
Moreover, in the method according to the aspect of the present invention, the metallic elements included in the oxide semiconductor layer may further include at least one or both of gallium and zinc.
According to the aspect of the present invention, target compatibility with large mass production facilities is increased, and thus production costs can be reduced.
Moreover, in the method according to the aspect of the present invention, the forming of the gate electrode, the forming of the gate insulating layer, the forming of the oxide semiconductor layer, and the forming of the source electrode and the drain electrode may be performed in listed order.
According to the aspect of the present invention, compatibility with production line facilities (existing facilities) for amorphous silicon TFTs for use in liquid crystal displays is increased, and thus production costs can be reduced.
Moreover, the method according to the aspect of the present invention may further include forming a protective layer on the oxide semiconductor layer.
According to the aspect of the present invention, it is possible to obtain the bottom gate thin film transistor which is capable of reducing process damage on the back channel side of the oxide semiconductor layer.
Moreover, in the method according to the aspect of the present invention, the forming of the oxide semiconductor layer, the forming of the gate insulating layer, the forming of the gate electrode, and the forming of the source electrode and the drain electrode may be performed in listed order.
According to the aspect of the present invention, it is possible to obtain the thin film transistor which is capable of reducing parasitic capacitance.
Moreover, an organic EL display device according to an aspect of the present invention includes any of the aforementioned thin film transistors, the organic EL display device including: pixels arranged in a matrix; and organic elements each formed corresponding to a different one of the pixels, wherein the thin film transistor is a driving transistor which drives the organic EL elements.
According to the aspect of the present invention, the thin film transistor having high reliability and high robustness is used as the driving transistor which drives the organic EL elements, and thus it is possible to achieve the organic EL display device superior display performance.
The following describes an embodiment of the present invention with reference to the accompanying drawings. The embodiment described below is merely a preferred illustration of the present invention. Values, shapes, materials, components, arrangement and connection of the components, processes (steps), order of the processes, and the like shown in the following embodiment are merely illustrative and are not intended to limit the present invention. Therefore, among the components of the embodiment below, components not recited in any one of independent claims are described as arbitrary components.
The figures are schematic illustration and do not necessarily limit the present invention to that precisely shown. In the figures, the same reference sign is used to refer to substantially the same component, and description already set forth is may be omitted or simplified.
First, the following describes a thin film transistor 1 according to the embodiment of the present invention with reference to
As illustrated by
The thin film transistor 1 includes a substrate 10, an undercoat layer 20, a gate electrode 30, a gate insulating layer 40, an oxide semiconductor layer 50, a protective layer 60, a source electrode 70S, and a drain electrode 70D.
The following describes in detail each component of the thin film transistor 1 according to the embodiment.
The substrate 10 is a glass substrate made of a glass material such as quartz glass, alkali-free glass, and high heat-resistant glass. It is to be noted that the substrate 10 is not limited to the glass substrate and may be a resin substrate or the like. Moreover, the substrate 10 is not a rigid substrate but may be a flexible substrate including a single layer of a film material such as polymide, polyethylene terephthalate, and polyethylene naphthalate, or stacked layers of these.
The undercoat layer 20 is formed on the substrate 10. The undercoat layer 20 is formed to prevent impurities such as sodium and phosphorus included in the substrate 10 (glass substrate) or moisture permeated from the air from entering the gate electrode 30, the gate insulating layer 40, and the oxide semiconductor layer 50.
The undercoat layer 20 is a single layer insulating layer of an oxide insulating layer or a nitride insulating layer, or a stacked insulating layer including an oxide insulating layer and a nitride insulating layer. In one instance, a single layer film of silicon nitride (SiNx), silicon oxide (SiOy), silicon oxynitride (SiOyNx), or aluminum oxide (AlOx), or stacked films of these can be used as the undercoat layer 20. The film thickness of the undercoat layer 20 is preferably set to be from 100 to 500 nm. It is to be noted that the undercoat layer 20 is not necessarily formed.
The gate electrode 30 is above the substrate 10 and is pattern-formed in a predetermined shape, on the undercoat layer 20. The gate electrode 30 is an electrode having a single layer structure or a multi-layer structure including a conductive material such as metal or an alloy thereof, and may include molybdenum (Mo), aluminum (Al), copper (Cu), tungsten (W), titanium (Ti), chrome (Cr), or molybdenum tungsten (MoW), for example. The film thickness of the gate electrode 30 is preferably set to be from 50 to 300 nm.
The gate insulating layer 40 is formed above the gate electrode 30. In the embodiment, the gate insulating layer 40 is formed on the undercoat 20 to cover the gate electrode 30. The gate insulating layer 40 is disposed between the gate electrode 30 and the oxide semiconductor layer 50.
The undercoat layer 40 is a single layer insulating layer of an oxide insulating layer or a nitride insulating layer, or a stacked insulating layer including an oxide insulating layer and a nitride insulating layer. The gate insulating layer 40 is a single layer film of silicon oxide, silicon nitride, silicon oxynitride, tantalum oxide, or aluminum oxide, or stacked films of these. In the embodiment, the gate insulating layer 40 is a stacked film including a silicon oxide film and a silicon nitride film, for example. The film thickness of the insulating layer 40 can be designed by taking into consideration pressure resistance of the TFT or the like, and is preferably set to be from 50 to 500 nm, for example.
The oxide semiconductor layer 50 is used as a channel layer. In other words, the oxide semiconductor layer 50 is a semiconductor layer including a channel region opposing the gate electrode 30 with the gate insulating layer 40 between the channel region and the gate electrode 30. The oxide semiconductor layer 50 is formed in a predetermined shape, on the gate insulating layer 40.
A transparent amorphous oxide semiconductor (TAOS) is used for the material of the oxide semiconductor layer 50, for example. Metallic elements included in the oxide semiconductor layer 50 preferably include at least indium (In) and further at least one or both of gallium (Ga) and zinc (Zn).
The oxide semiconductor layer 50 in the embodiment includes InGaZnOx (IGZO) that is an oxide including indium (In), gallium (Ga), and zinc (Zn).
Moreover, the oxide semiconductor layer 50 includes fluorine (F). Specifically, fluorine is included in a region that is an internal region in the oxide semiconductor layer 50 and is close to the gate insulating layer 40. In other words, fluorine is included in a front channel side of the oxide semiconductor layer 50. Moreover, fluorine that is chemically bonded is included in the oxide semiconductor layer 50. It is to be noted that the region that is the internal region in the oxide semiconductor layer 50 and is close to the gate insulating layer 40 is a region which is on a side of the gate insulating layer 40 and is below at least the middle of the thickness of the oxide semiconductor layer 50.
The oxide semiconductor layer 50 in the embodiment includes a first region (region including fluorine) 51 which is a region including fluorine, and a second region (region including no fluorine) 52 which is a region including no fluorine. The first region 51 is a region on the side of the gate insulating layer 40 in the oxide semiconductor layer 50. That is to say, in the embodiment, fluorine is included only in the region on the side of the gate insulating layer 40 in the oxide semiconductor layer 50. For example, when the middle of the film thickness of the oxide semiconductor layer 50 is a reference point, the first region 51 is a region (lower layer) below the middle of the film thickness of the oxide semiconductor layer 50, and the second region 52 is a region (upper layer) above the middle of the film thickness of the oxide semiconductor layer 50.
It is to be noted that although fluorine is included in part of the region in the oxide semiconductor layer 50 in the embodiment, fluorine may be included in the whole region of the oxide semiconductor layer 50. In short, the second region 52 may be unnecessary.
The first region 51 has a film thickness of at least 5 nm, and the film thickness of the first region 51 is set to be 20 nm or more in the embodiment. Moreover, the oxide semiconductor layer 50 preferably has a film thickness of 20 nm or more.
Setting the film thickness of the first region 51 to be 5 nm or more makes it possible to sufficiently exert the aforementioned effects of including fluorine.
Moreover, even when hydrogen diffuses in oxide semiconductor layer 50 by annealing or the like, setting the film thickness of the first region 51 to be 20 nm or more enables the first region 51 including fluorine to block diffusing hydrogen. In the embodiment, since the first region 51 is close to the gate insulating layer 40, hydrogen entering the oxide semiconductor layer 50 from the gate insulating layer 40 can be blocked by the region (first region 51) close to the gate insulating layer 40 in the oxide semiconductor layer 50.
Moreover, setting the film thickness of the first region 51 to be at least 20 nm makes it possible to sufficiently perform process control of the oxide semiconductor layer 50. In other words, the film thickness of the oxide semiconductor layer 50 can be set to be at least 20 nm by setting the film thickness of the first region 51 to be at least 20 nm. With this, it is possible to readily perform deposition of the oxide semiconductor layer 50 by sputtering or the like, and patterning of the oxide semiconductor layer 50 by a photolithography or etching method, for example.
Moreover, the oxide semiconductor layer 50 has a fluorine concentration higher than at least a hydrogen concentration of the oxide semiconductor layer 50. In the embodiment, the fluorine concentration of the oxide semiconductor layer 50 is set to be 1×1022 atm/cm3 or more.
The protective layer 60 is formed on the oxide semiconductor layer 50. The protective layer 60 is a channel region protective layer which protects the channel region in the oxide semiconductor layer 50, and serves as an etching stopper layer. With this, it is possible to reduce process damage on a back channel side of the oxide semiconductor layer 50 in the bottom gate TFT. Moreover, in the embodiment, the protective layer 60 is an interlayer insulating layer formed on the whole surface of the substrate 10.
The protective layer 60 may be made of a material having an organic substance as a main component or may be made of an inorganic substance such as silicon oxide, silicon nitride, silicon oxynitride, and aluminum oxide. In the embodiment, the protective layer 60 is made of a material having an organic substance as a main component. It is to be noted that the protective layer 60 may be a single layer film or a film having stacked layers.
It is to be noted that a silicon oxide film has a less amount of hydrogen than a silicon nitride film. Accordingly, using the silicon oxide film as the protective layer 60 makes it possible to reduce performance degradation of the oxide semiconductor layer 50 caused by hydrogen. In addition, using an oxide aluminum film as the protective layer 60 makes it possible to block hydrogen or oxygen generated in an upper layer with the oxide aluminum film. Judging from the above, for example, a stacked film having a three layer structure of the silicon oxide film, the oxide aluminum film, and the silicon oxide film is preferably used as the protective layer 60.
Moreover, in the protective layer 60, openings (contact holes) are formed to penetrate part of the protective layer 60. The oxide semiconductor layer 50 is connected to the source electrode 70S and the drain electrode 70D via the openings of the protective layer 60.
The source electrode 70S and the drain electrode 70D are formed in a predetermined shape, on the protective layer 60. The source electrode 70S is connected to the oxide semiconductor layer 50 via one of the openings formed in the protective layer 60, and the drain electrode 70D is connected to the oxide semiconductor layer 50 via the other of the openings formed in the protective layer 60.
The source electrode 70S and the drain electrode 70D each are an electrode having a single layer structure including an conductive material or an alloy thereof, or a multi-layer structure of these. The source electrode 70S and the drain electrode 70D may include, for example, molybdenum (Mo), aluminum (Al), copper (Cu), tungsten (W), titanium (Ti), chrome (Cr), molybdenum tungsten alloy (MoW), or copper manganese allow (CuMN). The film thickness of the source electrode 70S and the drain electrode 70D is preferably set to be from 50 to 300 nm, for example.
Next, the method for manufacturing the thin film transistor 1 according to the embodiment will be described with reference to
First, as illustrated by
Next, as illustrated by
Next, as illustrated by
Next, as illustrated by
Next, as illustrated by
The oxide semiconductor layer 50 includes an InGaZnOx transparent amorphous oxide semiconductor. In this case, the oxide semiconductor layer 50 including InGaZnOx can be deposited by a vapor phase deposition method such as a sputtering method and a laser evaporation method.
Specifically, a target material including In, Ga, and Zn (for example, a polycrystalline sintered body having an InGaO3(ZnO)4 composition) is used, an argon (Ar) gas as an inert gas and a gas including oxygen (O2) as a reactive gas are introduced into a vacuum chamber, and voltage of a predetermined power density is applied to the target material. With this, an InGaZnOx film can be deposited.
Here, a first oxide semiconductor layer including fluorine (In—Ga—Zn—O:F) can be deposited by sputtering while introducing fluorine. The introduction (supply) of fluorine into the oxide semiconductor layer can be performed by including fluorine in a target or introducing a process gas including fluorine (NF3 gas, for example). Specifically, the first oxide semiconductor layer including fluorine can result from depositing the InGaZnOx film by sputtering using a target material including fluorine. Alternatively, the first oxide semiconductor layer including fluorine can result from depositing the InGaZnOx film using a gas including fluorine (NF3 gas, for example).
Then, a second oxide semiconductor layer including no fluorine (In—Ga—Zn—O) is deposited by sputtering or the like without introducing (supplying) fluorine. It is to be noted that in the embodiment the first oxide semiconductor layer and the second oxide semiconductor layer are continuously deposited in the same chamber.
Then, the oxide semiconductor layer 50 having the predetermined shape can be formed by patterning, using a photolithography or wet etching method, the oxide semiconductor film having a stacked structure of the first oxide semiconductor layer and the second oxide semiconductor layer.
Specifically, first, a resist having a predetermined shape is formed on the oxide semiconductor film, and part of the oxide semiconductor film in a region where the resist is not formed is removed by wet etching, thereby forming the oxide semiconductor layer 50 having an island shape. It is to be noted that when the oxide semiconductor film includes InGaZnOx, a chemical solution obtained by mixing, for example, phosphoric acid (H3PO4), nitric acid (HNO3), acetic acid (CH3COOH), and water may be used as an etching solution.
Next, as illustrated by
Then, the openings (contact holes) are formed in the protective layer 60 to expose part of the oxide semiconductor layer 50. Specifically, part of the protective layer 60 is etched away by a photolithography or etching method, thereby forming the openings above connection portions with the source electrode 70S and the drain electrode 70D in the oxide semiconductor layer 50. For example, when the protective layer 60 is a silicon oxide film, the openings can be formed in the silicon oxide film by a dry etching method such as a reactive ion etching (RIE) method. In this case, carbon tetrafluoride (CF4) and oxygen gas (O2), for example, can be used as an etching gas.
Next, as illustrated by
It is to be noted that, though not illustrated, for example, a heat treatment at 300° C. (annealing) is performed subsequently. This heat treatment makes it possible to reduce oxygen deficiency in the oxide semiconductor layer 50 to stabilize characteristics of the oxide semiconductor layer 50.
The following describes an operational effect of the thin film transistor 1 according to the embodiment together with the background to the present invention.
The electrical characteristics of oxide semiconductor TFTs including an oxide semiconductor layer are susceptible to oxygen or hydrogen. For this reason, the oxide semiconductor TFTs have a problem with stability and reliability.
As disclosed by PTL 2 and NPL 2, it has been previously reported that the stability and reliability can be increased by improving an interface between an insulating layer and an oxide semiconductor layer.
For example, NPL 2 has reported that fluorine is compensated in a dangling bond site of In included in an oxide semiconductor layer (IGZO) by improving an interface with the oxide semiconductor layer using a gate insulating layer in which fluorine is included, thereby leading to increase the reliability.
In addition, NPL 2 has reported that the oxide semiconductor layer (IGZO) is measured by secondary ion mass spectrometry (SIMS) to observe no fluorine included in a bulk of IGZO.
After the inventors also actually verified whether fluorine was diffused in an oxide semiconductor layer (IGZO) by heat or the like using an insulating layer in which fluorine is included, they were not able to confirm desorption of fluorine by a thermal desorption method until the temperature reaches 500° C. or higher. This indicates that fluorine has a stable structure in the oxide semiconductor layer, and as shown by NPL 2, it is considered that the gate insulating layer in which fluorine is included merely produces an improvement effect in the interface between the insulating layer and the oxide semiconductor layer.
However, variation in the characteristics or degradation of the reliability of an oxide semiconductor TFT is caused not only by an interface between an insulating layer and an oxide semiconductor layer but also by process damage resulting from hydrogen or the like in a manufacturing process. Therefore, it is not sufficient to merely improve the interface between the insulating layer and the oxide semiconductor layer.
The present invention has been conceived based on such knowledge, and the inventors have arrived at an idea of obtaining a thin film transistor having high reliability by including fluorine in the oxide semiconductor layer 50 as described above.
The inventors have conducted various experiments to verify whether a thin film transistor having high reliability is obtained by including fluorine in an oxide semiconductor layer. The following describes the experiments and analyses of the same. It is to be noted that in the following experiments an InGaZnOx film whose main components of metallic elements are In, Ga, and Zn is used as the oxide semiconductor layer 50.
First, a point that oxygen deficiency can be compensated by including fluorine in the oxide semiconductor layer 50 will be described with reference to
Charge carriers are generated by oxygen deficiency (desorption of oxygen) to decrease a resistance value of the oxide semiconductor layer 50. As illustrated by
By contrast, a sheet resistance value in the case where fluorine is included in the oxide semiconductor layer 50 (IGZO including F) is a measurement limit (>1×1010Ω/□) and is higher than the sheet resistance value in the case fluorine is not included in the oxide semiconductor layer 50.
This is because, since fluorine has higher binding energy with metal than oxygen, including fluorine in the oxide semiconductor layer 50 enables fluorine to eliminate dangling bonds or an unstable site caused by the oxygen deficiency in the oxide semiconductor layer 50.
It is clear from these results that including fluorine in the oxide semiconductor layer 50 results in a structure in which charge carriers are less likely to be generated, that is, a structure which compensates the oxygen deficiency to be insensitive to the oxygen deficiency.
Next, a point that hydrogen resistance can be improved by including fluorine in the oxide semiconductor layer 50 will be described with reference to
As illustrated by
As illustrated by
In general, if hydrogen is included in an oxide semiconductor layer, the included hydrogen bonds with oxygen in the oxide semiconductor layer to generate charge carriers.
In view of, even if hydrogen is included in the oxide semiconductor layer, including fluorine in the oxide semiconductor layer and bonding fluorine with the oxide semiconductor layer prevent the included hydrogen from bonding with the oxide semiconductor layer. It is presumed that since fluorine has one valence arm, there is no valence arm available even if hydrogen enters and hydrogen is inert. As just described, including fluorine in the oxide semiconductor layer makes it possible to prevent the generation of the charge carriers in the oxide semiconductor layer. In short, including fluorine in the oxide semiconductor layer makes it possible to improve the hydrogen resistance.
Next, a point that a structure of the oxide semiconductor layer 50 is stabilized by including fluorine in the oxide semiconductor layer 50 will be described with reference to
As illustrated by
Moreover, as illustrated by
Furthermore, as illustrated by
It is clear from the results shown in
As just described, including fluorine in the oxide semiconductor layer 50 results in the metallic elements included in the oxide semiconductor layer 50 being chemically bonded with fluorine, which makes it possible to stabilize the structure of the oxide semiconductor layer 50. With this, it is possible to obtain a thin film transistor having high reliability.
As illustrated by
This is because oxygen desorbs from Zn—O bonds to destabilize Zn, which causes the desorption of Zn. A thermal desorption temperature can be used as a physical property index of an oxide semiconductor layer, and an increase in the thermal desorption temperature indicates that a structure of the oxide semiconductor layer is stabilized.
As just described, also from the standpoint of the thermal desorption temperature of Zn, including fluorine in the oxide semiconductor layer 50 results in the metallic elements included in the oxide semiconductor layer 50 being chemically bonded with fluorine, which makes it possible to stabilize the structure of the oxide semiconductor layer 50.
Fluorine is included in the oxide semiconductor layer 50 in the thin film transistor 1 according to the embodiment. In the embodiment, especially, fluorine is included in the region that is the internal region in the oxide semiconductor layer 50 and is close to the gate insulating layer 40.
With this, as mentioned above, not only the oxygen deficiency in the oxide semiconductor layer 50 can be compensated, but also the hydrogen resistance of the oxide semiconductor layer 50 can be improved, and further the structure of the oxide semiconductor layer 50 can be stabilized. Therefore, it is possible to achieve the thin film transistor 1 having high reliability and high robustness.
The following describes an example where the thin film transistor 1 according to the aforementioned embodiment is applied to a display device, with reference to
The above-mentioned thin film transistor 1 can be used as a switching transistor SwTr and a driving transistor DrTr of an active matrix substrate in the organic EL display device.
As illustrated by
The TFT substrate 110 in the embodiment includes the above-mentioned thin film transistor 1. Pixels 120 are arranged in a matrix in the TFT substrate 110, and a pixel circuit is included in each pixel 120.
Each of the organic EL elements 130 is formed corresponding to a different one of the pixels 120, and light emission of the organic EL element 130 is controlled by the pixel circuit included in the corresponding pixel 120. Each organic EL element 130 is formed on an interlayer insulating layer (planarizing layer) formed to cover thin film transistors.
Moreover, the organic EL element 130 has a configuration in which the EL layer 132 is disposed between the anode 131 and the cathode 133. Furthermore, a hole transport layer is formed stacked between the anode 131 and the EL layer 132, and an electron transport layer is formed stacked between the EL layer 132 and the cathode 133. It is to be noted that other function layers may be formed between the anode 131 and the cathode 133. In addition to the EL layer 132, a function layer to be formed between the anode 131 and the cathode 133 is an organic layer including an organic material.
Each pixel 120 is driven and controlled by a corresponding one of the pixel circuits. Moreover, in the TFT substrate 110, gate lines (scanning lines) 140 are disposed along the row direction of the pixels 120, source lines (signal lines) 150 are disposed along the column direction of the pixels 120 to cross the gate lines 140, and power supply lines (not illustrated in
The gate lines 140 are connected, on a row by row basis, to the gate electrodes of the switching transistors included in the respective pixel circuits. The source lines 150 are connected, on a column by column basis, to the source electrodes of the switching transistors. The power supply lines are connected, on a column by column basis, to the drain electrodes of the driving transistors included in the respective pixel circuits.
As illustrated by
The switching transistor SwTr includes: a gate electrode G1 connected to the gate line 140; a source electrode S1 connected to the source line 150; a drain electrode D1 connected to the capacitor C and a gate electrode G2 of a second thin film transistor DrTr; and an oxide semiconductor layer (not illustrated). When a predetermined voltage is applied to the gate line 140 and the source line 150 connected to the switching transistor SwTr, the voltage applied to the source line 150 is held as data voltage in the capacitor C.
The driving transistor DrTr includes: the gate electrode G2 connected to the drain electrode D1 of the switching transistor SwTr and the capacitor C; a drain electrode D2 connected to the power supply line 160 and the capacitor C; a source electrode S2 connected to the anode 131 of the organic EL element 130; and an oxide semiconductor layer (not illustrated). The driving transistor DrTr supplies current corresponding to data voltage held in the capacitor C from the power supply line 160 to the anode 131 of the organic EL element 130 via the source electrode S2. With this, in the organic EL element 130, drive current flows from the anode 131 to the cathode 133, which causes the EL layer 132 to emit light.
It is to be noted that the organic EL display device 100 having the above-described configuration uses an active-matrix system in which display control is performed for each pixel 120 at a cross-point between the gate line 140 and the source line 150. With this, the switching transistor SwTr and the driving transistor DrTr in each pixel 120 cause the corresponding organic EL element 130 to selectively emit light, and thus a desired image is displayed.
As above, the organic EL display device 100 in the embodiment uses, as the switching transistor SwTr and the driving transistor DrTr, the thin film transistor 1 having high reliability and high robustness, and thus it is possible to achieve an organic EL display device having superior reliability. In particular, the thin film transistor 1 is used as the driving transistor DrTr driving the organic EL element 130, and thus it is possible to achieve an organic EL display device having superior display performance.
As shown above, a thin film transistor and a method for manufacturing the same have been described based on the aforementioned embodiment, but the present invention is not limited to the embodiment.
For example, the amorphous oxide semiconductor of InGaZnOx (IGZO) is used as the oxide semiconductor for use in the oxide semiconductor layer in the aforementioned embodiment, but the present invention is not limited to this. An oxide semiconductor including In such as a polycrystalline oxide semiconductor like InGaO can be used.
Moreover, the aforementioned embodiment has described the bottom gate thin film transistor in which the gate electrode 30, the gate insulating layer 40, and the oxide semiconductor layer 50 are stacked upward in listed order on the substrate 10, but the present invention is not limited to this.
For example, as illustrated by
Using the top gate thin film transistor makes it possible to reduce parasitic capacitance.
Moreover, the aforementioned embodiment has described the organic EL display device as the display device including the thin film transistor, but the present invention is not limited to this. For example, the thin film transistor according to the aforementioned embodiment can be applied to another display device such as a liquid crystal display device.
In this case, the organic EL display device (organic EL panel) can be used as a flat panel display. For example, the organic EL display device can be used as a display panel of any electronic device such as a television set, a personal computer, and a cellular phone.
Moreover, the scope of the present invention includes an embodiment obtained by adding various modifications to each embodiment or variation that may be conceived by those skilled in the art or an embodiment obtained by arbitrarily combining components and functions of the embodiment or variation without departing from the spirit of the present invention.
The thin film transistor according to the present invention can be widely used in a variety of electric equipment including the thin film transistor, such as display devices (display panels) like organic EL display devices, television sets, personal computers, and cellular phones.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-127524 | Jun 2014 | JP | national |
The present application is a National Phase of International Application Number PCT/JP2015/003041, filed Jun. 17, 2015, which claims priority to Japanese Application Number 2014-127524, filed Jun. 20, 2014.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/003041 | 6/17/2015 | WO | 00 |
