JP2007123661A - Thin-film transistor and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-film transistor having an active layer capable of being deposited at a room temperature by suppressing variations in performance of individual products. <P>SOLUTION: By using InGaSnO<SB>x</SB>(4≤x≤5) as a material of the thin-film transistor, an amorphous InGaSnO<SB>x</SB>(4≤x≤5) semiconductor can be formed on a flexible board at a room temperature with a wide process window, and the thin-film transistor having high bending strength can be manufactured while suppressing the variations between products at the minimum. Further, a sputtering method, especially, an InGaSnO<SB>5</SB>target is used as the manufacturing method to make an oxygen flow rate 2-4%, and thus, mobility of about 1 cm<SP>2</SP>/Vs can be stably obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a thin film transistor using, as an active layer, a non-single-crystal material mainly composed of InGaSnO _x (4 ≦ x ≦ 5), which can be used as an element constituting an electronic circuit.

  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 (TFTs). It has been.

  Silicon or silicon compounds are widely used for the active layers of these transistors. Single-crystal silicon is 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. .

  A flexible display expected as a substitute for paper is required to use a flexible substrate. Since such a substrate generally has a low heat-resistant temperature, further reduction in the process temperature is required. CVD is widely used for producing an amorphous silicon thin film. In particular, plasma CVD decomposes silane, which is a raw material gas, so that it can be formed at a lower temperature than thermal CVD, but still 200 to 300 ° C. The reaction temperature is required.

In recent years, an oxide semiconductor InGaZnO ₄ which can be formed at room temperature and has a field effect mobility equal to or higher than that of amorphous silicon has been announced, and has shown the possibility as an active layer of a thin film transistor. (For example, refer nonpatent literature 1.)

InGaZnO ₄ is a material known as a transparent conductive film, but it has succeeded in reducing oxygen vacancies as a carrier source and controlling off current by controlling the oxygen partial pressure during film formation. Yes. Moreover, since an amorphous state can be easily obtained, it is suitable for application to a flexible display.

K. Nomura, H. Ohta, A. Takagi, T. Kamiyama, M. Hirono, H. Hosono, “Nature”, November 25, 2004, 432, p. 488-492

For application to a display, a sputtering method capable of uniformly forming a film over a large area is suitable. However, when this InGaZnO ₄ is used for an active layer of a thin film transistor, a field effect mobility required for a display element is 1 cm ² / V ·. The range of the oxygen flow rate at which field effect mobility near s can be obtained is very narrow (see FIG. 1), and there is a problem that variations occur in products.

  The present invention has been made in view of the state of the related art, and by using a material having a sufficiently wide process window at the time of film formation, it is possible to suppress variation in performance of individual products at a low temperature. An object of the present invention is to provide a thin film transistor that can be formed.

In order to achieve the above object, a first invention is a thin film transistor characterized by using an InGaSnO _x (4 ≦ x ≦ 5) thin film as an active layer. When this material is used, a sufficient range can be provided in the range of the oxygen flow rate ratio during film formation (see FIG. 1).

The second invention is the thin film transistor according to claim 1, wherein the InGaSnO _x (4 ≦ x ≦ 5) is a non-single-crystal thin film. By using a non-single crystal material, resistance to bending is increased, and application to a flexible display becomes possible.

  The third invention is the thin film transistor according to claim 1 or 2, wherein the substrate of the thin film transistor is a flexible substrate. By selecting appropriate gate insulating films and electrode materials and forming them on a flexible substrate, the entire substrate including the transistor can be bent.

The fourth invention is a method of manufacturing a thin film transistor according to any one of claims 1 to 3, wherein an InGaSnO _x (4 ≦ x ≦ 5) thin film is formed by a sputtering method. By using the sputtering method, a uniform film can be formed over a large area.

The fifth invention is the method of manufacturing a thin film transistor according to claim 4, wherein an InGaSnO _x (4 ≦ x ≦ 5) thin film is formed using an InGaSnO ₅ target. By using an InGaSnO ₅ target, formation of an InGaSnO _x (4 ≦ x ≦ 5) thin film is facilitated.

In the sixth invention, the oxygen flow rate ratio in the sputtering method is 2 to 4%. By setting the oxygen flow rate ratio, that is, the oxygen flow rate / (Ar flow rate + oxygen flow rate) to 2 to 4%, a mobility of about 1 cm ² / V · s can be stably obtained.

From the above configuration, the present invention has the following effects.
By using InGaSnO _x (4 ≦ x ≦ 5) as the material of the active layer of the thin film transistor, a non-single-crystal material InGaSnO _x (4 ≦ x ≦ 5) semiconductor is formed over a flexible substrate at room temperature with a wide process window. Thus, a bent thin film transistor can be manufactured with minimum variation between products.

  Embodiments of the present invention will be described in detail below with reference to FIGS.

An example of the thin film transistor of the present invention is shown in FIG. Although the bottom gate type is used in this embodiment mode, a top gate type may be used. In the example of FIG. 2, InGaSnO _x (4 ≦ x ≦ 5) is used for the active layer 4.

  Next, a manufacturing method is demonstrated using FIG. First, the substrate 1 is prepared (FIG. 3A). As a material for the substrate 1, a lightweight and flexible plastic substrate can be used, but a glass substrate, a silicon substrate, or the like can also be used. Examples of flexible plastic substrates include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyimide (PI), polyetherimide (PEI), polystyrene (PS), polyvinyl chloride ( PVC), polyethylene (PE), polypropylene (PP), nylon and the like can be used. However, surface treatment with UV, plasma, or the like may be performed to improve adhesion.

  Next, the gate electrode 2 is formed on the substrate 1 (FIG. 3B). The material, manufacturing method, and patterning method of the gate electrode are not limited. Examples include mask vapor deposition (including sputtering), screen printing, and the like of metals, alloys, and transparent conductive films. In the case of screen printing, a metal paste such as Pt, Au, Ag, Cu, or Ni, or an organic conductor paste such as polyethylenedioxythiophene (PEDOT) or polyaniline (PANI) can be used.

Next, the gate insulating film 3 is produced (FIG. 3C). The material, manufacturing method, and patterning method of the gate insulating film 3 are not limited. For example, SiO ₂ , SiN, Al ₂ O ₃ or the like can be used, but it is preferable to use a high dielectric constant (high-k) material such as HfO ₂ or Y ₂ O ₃ .

Next, the active layer 4 is formed (FIG. 3D). InGaSnO _x (4 ≦ x ≦ 5) is used as the material. The formation method is preferably a sputtering method capable of uniform film formation over a large area, and can be easily formed using an InGaSnO ₅ target. Other methods such as pulsed laser deposition (PLD) are also possible.

  Next, the source / drain electrodes 5 are formed to complete the thin film transistor (FIG. 3E). There are no limitations on the material, fabrication method, and patterning method of the source / drain electrodes. Examples include mask vapor deposition (including sputtering), screen printing, and the like of metals, alloys, and transparent conductive films. 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.

When InGaSnO _x (4 ≦ x ≦ 5) is used as the active layer, a mobility of about 1 cm ² / V · s can be stably obtained in a wide range where the oxygen flow rate ratio is 2% to 4%.

PEN was used as the substrate 1 (FIG. 3 (a)), and tin-doped indium oxide (ITO) was formed to a thickness of 50 nm by DC magnetron sputtering, and patterned to form the gate electrode 2 (FIG. 3). 3 (b)). For patterning, general lithography was used, and the ITO layer was processed by wet etching. Next, 300 nm of SiO ₂ was formed by plasma CVD at a substrate temperature of 50 ° C. or less to form a gate insulating film 3 (FIG. 3C). Using an InGaSnO ₅ target, an InGaSnO _x (4 ≦ x ≦ 5) thin film having a thickness of 50 nm is formed by an RF magnetron sputtering method at an oxygen flow rate ratio (oxygen flow rate / (Ar flow rate + oxygen flow rate)) of 2%. The active layer 4 was formed by patterning (FIG. 3D). Finally, ITO was deposited to a thickness of 50 nm by DC magnetron sputtering and patterned to form source / drain electrodes 5 (FIG. 3E), thereby completing a non-single-crystal thin film transistor (FIG. 2). The channel length is 50 μm and the channel width is 800 μm.

As a result of measuring the field effect mobility of this element, 1 cm ² / V · s was obtained.

Similarly, devices were produced at an oxygen flow rate ratio of 4% and 6%, and 1.4 and 0.01 cm ² / V · s were obtained, respectively.

  An example of the use of such a thin film transistor is a flexible display.

It is side surface sectional drawing which shows the structural example of the thin-film transistor of this invention. It is side surface sectional drawing which shows an example of the manufacturing process of the thin-film transistor of this invention. InGaZnO is a diagram showing a field-effect mobility of the relationship between the device fabricated with the oxygen flow ratio during the deposition of _{InGaSnO x (4 ≦ x ≦ 5} ) ₄ and the present invention.

Explanation of symbols

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

Claims (6)

A thin film transistor using an InGaSnO _x (4 ≦ x ≦ 5) thin film as an active layer. The thin film transistor according to claim 1, wherein the InGaSnO _x (4 ≦ x ≦ 5) is a non-single-crystal thin film.   The thin film transistor according to claim 1 or 2, wherein the substrate of the thin film transistor is a flexible substrate. 4. The method of manufacturing a thin film transistor according to claim 1, wherein an InGaSnO _x (4 ≦ x ≦ 5) thin film is formed by a sputtering method. The method for manufacturing a thin film transistor according to claim 4, wherein an InGaSnO ₅ target is used as a target used in the sputtering method.   6. The method of manufacturing a thin film transistor according to claim 4, wherein an oxygen flow rate ratio in the sputtering method is 2 to 4%.

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