JP2007123698A - Thin-film transistor and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-film transistor in which an amorphous oxide semiconductor thin film containing no In and having small environmental load is deposited as an active layer, and to provide a method of manufacturing the same. <P>SOLUTION: Using a target made of ZnGa2O4 or SnGa2O5, a thin film made of any one of ZnGa2Ox (3≤x≤4) or SnGa2Ox (4≤x≤5) is deposited on a flexible board at a room temperature by a sputtering method, thereby forming the active layer of the thin-film transistor which contains no In. Thus, the problem is solved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a thin film transistor using a non-single crystal material thin film that can be used as an element constituting an electronic circuit as an active layer, and a method for manufacturing the same.

  Field effect transistors are used as various switching elements such as unit electronic elements of semiconductor memory integrated circuits, high frequency signal amplifying elements, liquid crystal driving elements, and the thinned transistors are well known as thin film transistors (hereinafter referred to as TFTs). .

  Silicon or silicon compounds are widely used for the active layers of these transistors. In addition, silicon single crystals are used for high-frequency amplifying elements and integrated circuit elements that require high-speed operation, and amorphous silicon is used for display elements that are sufficient for low-speed operation due to the demand for large area. ing.

On the other hand, a TFT using a flexible substrate is required for a flexible display. Since a substrate for producing such a TFT generally has a low heat-resistant temperature, it is necessary to further lower the process temperature for forming a thin film.
CVD is widely used for the production of the above-mentioned amorphous silicon thin film, and in particular, plasma CVD decomposes silane, which is a raw material gas, to form a thin film, so that it is formed at a lower temperature than thermal CVD. it can.
However, even for this plasma CVD thin film formation, a reaction temperature of 200 to 300 ° C. is required. For this reason, it is difficult to form a thin film on a substrate having low heat resistance.

  In recent years, an oxide semiconductor InGaZnO 4 has been proposed as a material that can be formed at room temperature and has a field effect mobility equivalent to or higher than that of amorphous silicon, and has shown the possibility of being an active layer constituting a thin film transistor ( Non-patent document 1).

K. Nomura, H .; Ohta, A .; Takagi, T .; Kamiyama, M .; Hirano, H .; Hosono: Nature 432 (2004) 488.

  InGaZnO 4 described in Non-Patent Document 1 is a material known as a transparent conductive film. By controlling the oxygen partial pressure during film formation, oxygen vacancies serving as carrier sources are reduced, and off. It has succeeded in reducing the current. In addition, since an amorphous thin film can be easily obtained, it is suggested that it is suitable for application to a flexible display.

However, the amount of In used in the above-described oxide semiconductor InGaZnO 4 is decreased because the amount of buried crust is small. In addition, In is used in many fields as a material for transparent electrodes, and the amount of use has increased rapidly with the increase in production of flat panel displays (FPDs) in particular, so the price is rising.
For this reason, in order to expand the application of FPD, development of a material that does not contain In is demanded, and a thin film used for a TFT is also demanded of a material that does not contain In that has a small environmental load.
In view of the above problems, an object of the present invention is to provide a non-single-crystal oxide semiconductor containing no In, a TFT in which a thin film made of the semiconductor is formed, and a method for manufacturing the TFT.
Another object of the present invention is to provide a thin film transistor made of a non-single-crystal oxide semiconductor capable of forming a thin film at room temperature.

In order to achieve the above object, a first invention is a thin film transistor having an active layer made of a ZnGa2Ox (3≤x≤4) thin film.
The material of the active layer has a spinel structure when crystallized, and the carrier movement path is considered to be due to the sharing of the edge of the GaO6 oxygen face structure, and this path is basically followed even in the amorphous state. It is done. Although it is a material that does not contain In, it has field effect mobility and semiconductor characteristics.

According to a second aspect of the present invention, there is provided a thin film transistor having an active layer made of a SnGa2Ox (4 ≦ x ≦ 5) thin film.
The material of the active layer is a material that does not contain In, but has field effect mobility and semiconductor characteristics.

A third aspect of the present invention is the thin film transistor according to any one of claims 1 and 2, wherein the active layer is a non-single crystal thin film.
Thus, by using a non-single crystal material, resistance to bending is increased, and film formation can be performed even at a low temperature, which facilitates manufacturing and enables application to a flexible display.

According to a fourth aspect of the present invention, there is provided the thin film transistor according to any one of claims 1 to 3, wherein the active layer is formed on a flexible substrate.
By selecting appropriate gate insulating films and electrode materials and forming them on a flexible substrate, including these, it is possible to bend the entire substrate including the transistor, and it can be formed without the use of a glass substrate. I can plan.

The fifth invention of the present invention is the thin film transistor according to any one of claims 1 to 4, wherein the active layer is a thin film formed by a sputtering method.
By using the sputtering method in this way, a uniform active layer can be formed over a large area.

A sixth invention of the present invention is a method of manufacturing a thin film transistor, wherein an active layer made of a ZnGa2Ox (3 ≦ x ≦ 4) thin film is formed by a sputtering method using a ZnGa2O4 target.
As described above, the use of the ZnGa2O4 target facilitates the formation of an active layer made of a ZnGa2Ox (3 ≦ x ≦ 4) thin film.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a thin film transistor, wherein an active layer made of a SnGa2Ox (4 ≦ x ≦ 5) thin film is formed by a sputtering method using a SnGa2O5 target.
As described above, the use of the SnGa2Ox target facilitates the formation of an active layer made of a SnGa2Ox (4 ≦ x ≦ 5) thin film.

With the above structure, the present invention can be a thin film transistor using ZnGa2Ox (3 ≦ x ≦ 4) or SnGa2Ox (4 ≦ x ≦ 5) that does not contain In as the material of the active layer. It was.
In addition, since the active layer can be formed at a low temperature without using In, a thin film transistor having a low environmental load can be manufactured at a low temperature at a room temperature using a flexible substrate.

Embodiments of the present invention will be described below in detail with reference to FIGS.
An example of the thin film transistor of the present invention is shown in FIG. The following description is based on the bottom gate type, but it goes without saying that a top gate thin film transistor may be used.
First, the substrate 1 is prepared (see FIG. 2A).
Here, various materials can be used as the material of the substrate 1, and a lightweight and flexible plastic substrate can also be used.
Examples of the plastic substrate include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyimide (PI), polyetherimide (PEI), polystyrene (PS), and polyvinyl chloride (PVC). Polyethylene (PE), polypropylene (PP), nylon and the like can be used. In addition, it is preferable to perform surface treatment with UV, plasma, or the like in order to improve adhesion.

Next, the gate electrode 2 is formed on the substrate 1 (see FIG. 2B).
The material, manufacturing method, and patterning method of the gate electrode 2 are not particularly limited. Examples thereof include a method of forming a film by vapor deposition (including sputtering) using a metal, an alloy, or a transparent conductive material, and screen printing of the material. However, it is not limited to the above contents. In the case of screen printing, a metal paste such as Pt, Au, Ag, Cu, or Ni, or an organic conductor paste such as polyethylene dioxinthiophene (PEDOT) or polyaniline (PANI) can be used.

Next, the gate insulating film 3 is produced (see FIG. 2C).
The material, manufacturing method, and patterning method of the gate insulating film 3 are not particularly limited.
For example, SiO2, SiN, Al2O3, HfO2 or Y2O3 can be used as the material, and it is particularly preferable to use a high dielectric constant (high-k) material such as HfO2 or Y2O3.

Next, the active layer 4 is formed (see FIG. 2D).
As the material of the active layer 4, ZnGa2Ox (3 ≦ x ≦ 4) or SnGa2Ox (4 ≦ x ≦ 5) can be used. The active layer 4 is preferably formed by a sputtering method capable of forming a large-area uniform film, and can be easily formed by using a ZnGa2O4 target or a SnGa2O5 target, respectively. As a method other than the sputtering method, other methods such as pulse laser deposition (PLD) are possible.

Next, the source / drain electrodes 5 are formed (see FIG. 2E).
The material, production method, and patterning method of the source / drain electrodes are not particularly limited. Examples thereof include a method of forming a film by vapor deposition (including sputtering) using a metal, an alloy, or a transparent conductive material, and screen printing of the material. However, it is not limited to the above contents. In the case of screen printing, a metal paste such as Pt, Au, Ag, Cu, or Ni, or an organic conductor paste such as PEDOT or PANI can be used.
Through the above steps, a thin film transistor was obtained (see FIG. 1).

Example 1
Using PEN as the substrate 1 (see FIG. 2A), an Al layer having a thickness of 50 nm was formed on the base material 1 by dc magnetron sputtering and patterned to form a gate electrode 2 ( (Refer FIG.2 (b)).
The patterning for forming the gate electrode 2 was performed by processing the Al layer by wet etching using general lithography.
Next, a SiO 2 film having a thickness of 300 nm was formed by plasma CVD at a substrate temperature of 50 ° C. or less to form a gate insulating film 3 (see FIG. 2C).
Next, a ZnGa2Ox (3 ≦ x ≦ 4) thin film having a thickness of 50 nm was formed by a rf magnetron sputtering method using a ZnGa2O4 target, and patterned using general lithography to form an active layer 4 ( (Refer FIG.2 (d)).
Finally, an Al layer was formed to a thickness of 50 nm by dc magnetron sputtering and patterned to form source / drain electrodes 5 (see FIG. 2E).
In this way, a non-single-crystal thin film transistor having a channel length of 50 μm and a channel width of 800 μm was manufactured (see FIG. 1).

(Example 2)
The same conditions as in Example 1 were used except that SnGa2O5 was used as the active layer 4 instead of ZnGa2O4 used in Example 1, and the formed active layer was SnGa2Ox (4 ≦ x ≦ 5). A non-single-crystal thin film transistor having a channel length of 50 μm and a channel width of 800 μm was manufactured.

4A and 4B are a top view and a side view illustrating an example of a thin film transistor of the present invention. Explanatory drawing which shows an example of the manufacturing process of the thin-film transistor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Gate electrode 3 ... Gate insulating film 4 ... Active layer 5 ... Source / drain electrode

Claims (7)

A thin film transistor comprising an active layer made of a ZnGa2Ox (3≤x≤4) thin film. A thin film transistor having an active layer made of a SnGa2Ox (4 ≦ x ≦ 5) thin film. The thin film transistor according to claim 1, wherein the active layer is a non-single crystal thin film. 4. The thin film transistor according to claim 1, wherein the active layer is formed on a flexible substrate. 5. The thin film transistor according to claim 1, wherein the active layer is a thin film formed by a sputtering method. A method of manufacturing a thin film transistor, wherein an active layer made of a ZnGa2Ox (3≤x≤4) thin film is formed by sputtering using a ZnGa2O4 target. A method of manufacturing a thin film transistor, wherein an active layer made of a SnGa2Ox (4 ≦ x ≦ 5) thin film is formed by a sputtering method using a SnGa2O5 target.

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