KR20120069131A - A method for preparing a thin film transistor - Google Patents

Abstract

PURPOSE: A method for manufacturing a thin film transistor is provided to improve an electric property of the thin film transistor by including an active layer. CONSTITUTION: A substrate with a preset curvature and flexibility is prepared. An active layer(20) made of oxide semiconductor is formed on the convex surface of the substrate. Compressed stress is applied to the active layer by removing the curvature of the substrate to make the substrate horizontal. A source electrode(30), a drain electrode, a gate insulation layer(50), and a gate electrode(60) are formed on the active layer.

Description

Manufacturing method of thin film transistor {A METHOD FOR PREPARING A THIN FILM TRANSISTOR}

The present invention relates to a method for manufacturing a thin film transistor, and more particularly, to a method for manufacturing a thin film transistor having an active layer made of an oxide semiconductor.

The thin film transistor is used as an active switch element and is an essential component of a memory and a non-memory integrated circuit, and an organic light emitting diode display (OLED display) and a liquid crystal display (e. It is mainly used for liquid crystal display (LCD display).

The active layer of such a thin film transistor is usually composed of a semiconductor such as amorphous silicon or poly silicon. When the amorphous silicon is used as an active layer, it is applied to a circuit that operates at high speed due to low mobility of electrons as carriers. Hard. In addition, when the polycrystalline silicon is used, the yield voltage is reduced and the area for the integrated circuit is wasted because the threshold voltage of the thin film transistor is uneven due to polycrystallization and a compensation circuit is needed to compensate for the dispersion. The process steps required for formation are added to increase manufacturing time and costs.

In order to solve the above problems, there is no characteristic scattering problem as amorphous, and many studies have been made in the academic and industrial fields to use oxide semiconductors having high electron mobility in the active layer.

Representative examples of oxide semiconductors include amorphous multicomponent oxide semiconductors in which various metal elements are mixed on a zinc oxide (ZnO) base. Specific examples of such a multi-component oxide semiconductor include InGaZnO (Indium-Gallium-Zinc oxide; IGZO), ZnSnO (Zinc-Tin oxide; ZTO), ZnSnGaO (Zinc-Tin-Gallium oxide (ZTGO), and AlZnSnO (Aluminum-Zinc-Tin). AZTO), and HfInZnO (Hafnium-Indium-Zinc oxide; HIZO).

On the other hand, when forming an active layer of an oxide semiconductor in manufacturing a thin film transistor, an additional heat treatment process is essential to obtain a high electron mobility. Here, the heat treatment temperature for obtaining high electron mobility may vary depending on the combination and composition of metal elements constituting the oxide semiconductor, and heat treatment is usually performed in the range of 200 to 500 degrees. However, as the heat treatment temperature increases, the electron mobility increases to improve the electrical characteristics of the thin film transistor. However, when a substrate having a low heat resistance such as glass or a flexible plastic is used as the substrate for forming the thin film transistor, it is difficult to heat-treat at high temperature. There is a problem that the high electron mobility characteristic of the semiconductor cannot be obtained completely. In addition, even when the oxide semiconductor has the same composition, since the mobility of electrons is lower than that of a single crystal when amorphous, the heat treatment temperature must be very high in order to obtain high electron mobility such as a single crystal.

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a method of manufacturing a thin film transistor having an improved electrical property by having an active layer exhibiting high electron mobility.

In order to achieve the above object, the present invention comprises the steps of preparing a substrate having a predetermined curvature and flexibility; Forming an active layer of an oxide semiconductor on the convex surface of the substrate; Applying a compressive stress to the active layer by removing curvature of the substrate so that the substrate is horizontal; And forming a source electrode, a drain electrode, a gate insulating film, and a gate electrode on the active layer.

Here, the predetermined curvature may be defined as a state in which the substrate is bent to have a convex surface and a concave surface.

In the present invention as described above, since the compressive stress is applied when the active layer is formed of the oxide semiconductor, the active layer may exhibit high electron mobility even when heat treated at a low temperature, and the thin film transistor may be manufactured by having an active layer exhibiting high electron mobility. Therefore, a thin film transistor having excellent electrical characteristics can be provided.

1 is a process diagram showing a manufacturing method of a thin film transistor according to the present invention.
2 to 4 are reference diagrams for explaining a method of manufacturing a thin film transistor according to the present invention.

Hereinafter, the present invention will be described in detail.

The present invention is to enable the active layer to exhibit a high electron mobility even when the active layer is heat-treated at a low temperature by applying a compressive stress when forming the active layer provided in the thin film transistor, see the drawings for the manufacturing method of the thin film transistor according to the present invention The description is as follows.

First, a substrate 10 having a predetermined curvature and flexibility is prepared (see FIG. 1A). That is, the substrate 10 has flexibility to be deformed (for example, bent or curved) when a force is applied from the outside, and has a curvature so that the convex surface C1 and the concave surface C2 exist. It is. The substrate 10 maintains a state in which a tensile stress is applied as the substrate 10 has a curvature by an external force.

Here, the method of causing the substrate 10 to have a curvature is not particularly limited. Any one of a polymer film, a metal (for example, Al, Ti, etc.), and an oxide or nitride film (for example, SiO ₂ , Al ₂ O ₃ , TiN, TaN, etc.) may be formed on one side of the substrate 10. A method of chemically depositing or physically attaching one to break the stress balance of the substrate 10 to bend the substrate 10 may be applied. Also, as shown in FIG. 2, the substrate 10 is temporarily bonded to the first support 11 having a concave upper portion, and then the substrate 10 is maintained for a long time at a temperature higher than room temperature. The shape of 11 can be stored, and when the board | substrate 10 is about to memorize the shape, it can be made to have curvature by isolate | separating the 1st support base 11.

The material that can be used as the substrate 10 is not particularly limited, but non-limiting examples include glass, silicon, metal foil, plastic, and the like. Here, the plastic that can be used as the substrate 10 is not particularly limited, but non-limiting examples include polyimide (PI), polycarbonate (PC), polyethersulfone (PES), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), ethylene copolymer, polypropylene (PP), propylene copolymer, poly (4- Methyl-1-pentene (TPX), polyarylate (PAR), polyacetal (POM), polyphenylene oxide (PPO), polysulfone (PSF), polyphenylene sulfide (PPS), polyvinylidene chloride ( PVDC), polyvinyl acetate (PVAC), polyvinyl alcohol (PVAL), polyvinyl acetal, polystyrene (PS), AS resin, ABS resin, polymethyl methacrylate (PMMA), fluorocarbon resin, phenolic resin (PF), Melamine resin (MF), urea resin (UF), unsaturated polyester (UP), epoxy resin (EP), diallyl phthalate resin (DAP) ), Polyurethane (PUR), polyamide (PA) or mixtures thereof. Here, glass or silicon having hard properties is difficult to be deformed to a state with curvature due to its low flexibility. To facilitate this, the glass or silicon may have a curvature according to an external force applied thereto. Specifically, in the case of using a substrate having rigid properties such as glass or silicon, the thickness of the substrate may be 20 to 200 μm to have curvature.

In addition, the material that can be used as the first support 11 is not particularly limited. metal. Ceramics or polymers having heat resistance can be used.

Meanwhile, the second support 12 having a curvature corresponding to the substrate 10 may be temporarily bonded to the substrate 10 so that the substrate 10 may be stably maintained when the active layer is formed on the substrate 10 having the curvature. May be added (see FIG. 1B). That is, the second support 12 having a curvature corresponding to the substrate 10 is temporarily bonded to the concave surface C2 of the substrate 10 so that the substrate 10 maintains the curvature. It is fixed. In this case, the second support 12 may be convex only with the surface coupled to the substrate 10, and the other support 12 may be horizontal with respect to the ground. Such a material usable as the second support 12 is not particularly limited. metal. Ceramics or polymers having heat resistance can be used. As such, when the second support 12 is used to fix the substrate 10, deformation of the substrate 10 may be prevented from occurring during the manufacturing process, and the substrate 10 may be easily handled.

The method of temporarily bonding the substrate 10 and the second support 12 is not particularly limited. It is possible to use adhesives known in the art or to use physical bonding methods such as tongs or screws to facilitate separation.

Next, when the substrate 10 having curvature and flexibility is prepared, an oxide semiconductor is formed on the convex surface C1 of the substrate 10 and then heat treated to form the active layer 20 (see FIG. 1C). ). In this case, the method of forming the active layer 20 is not particularly limited as long as it is known in the art. Sputtering, pulsed laser deposition, atomic layer deposition, electron beam deposition, spin coating, spraying and inkjet printing (atmospheric pressure). In addition, the material usable as the oxide semiconductor is not particularly limited as long as it is known in the art. InGaZnO (Indium-Gallium-Zinc oxide; IGZO), ZnSnO (Zinc-Tin oxide; ZTO), ZnSnGaO (Zinc-Tin-Gallium oxide; ZTGO), AlZnSnO (Aluminum-Zinc-Tin oxide (AZTO), AlZnInSnO (Aluminum- Zinc-Indium-Tin oxide (AZITO), HfInZnO (Hafnium-Indium-Zinc oxide; HIZO), or the like. The temperature at which the oxide semiconductor is heat treated is not particularly limited. Heat treatment can be made in the range of 50 ~ 200 degrees.

On the other hand, if the active layer 20 is formed while the substrate 10 and the second support 12 are temporarily coupled, separating the substrate 10 and the second support 12 after the active layer 20 is formed. May be additionally performed.

After the active layer 20 is formed on the convex surface C1 of the substrate 10, the curvature of the substrate 10 is removed so that the compressive stress is applied to the active layer 20 (FIG. 1D). Reference). That is, as the external force is applied to the substrate 10 to remove the curvature of the substrate 10, the tensile stress existing in the substrate 10 disappears and the compressive stress is applied to the active layer 20.

Here, the method of removing the curvature of the substrate 10 is not particularly limited, but by temporarily coupling the horizontal third support 13 or the concave fourth support 14 and the substrate 10 (FIGS. 3 and 4). It is possible to remove the curvature of the substrate 10 by maintaining for a long time at room temperature or higher than room temperature. At this time, the support and the substrate 10 is coupled to the upper surface of the third support 13 and the concave surface C2 of the substrate 10 is coupled, the concave surface of the fourth support 14 and the substrate 10 The concave surface C2 is engaged. The material that can be used as the third support 13 and the fourth support 14 is not particularly limited. metal. Ceramics or polymers having heat resistance can be used.

In addition, a film made of a polymer film, a metal (for example, Al, Ti, etc.), and an oxide or a nitride (for example, SiO ₂ , Al ₂ O ₃ , TiN, TaN, etc.) is formed on the concave surface of the substrate 10. The curvature of the substrate 10 may be removed by chemically depositing or physically attaching any of them to break the stress balance of the substrate 10.

As described above, since the active layer 20 is formed by applying a compressive stress to the oxide semiconductor, the present invention may provide a thin film transistor having improved electrical properties by increasing electron mobility of the oxide semiconductor even when heat treatment is performed at a lower temperature than in the prior art. In other words, the oxide semiconductor exhibits high electron mobility as the s-electron orbits between the metal atoms overlap each other, and the present invention reduces the distance between the metal atoms by applying a compressive stress to the oxide semiconductor, thereby reducing the s-electron orbits. Since the overlap is increased, the electron mobility is increased.

Thereafter, the source electrode 30, the drain electrode 40, the gate insulating film 50, and the gate electrode 60 are sequentially formed on the active layer 20 to which the compressive stress is applied to manufacture a thin film transistor (see FIG. 1). (e)).

Source electrode 30, drain electrode 40 and gate electrode 60, and can be used without having a good electrical conductivity, it is not particularly limited if the active layer 20 and the electrical connection is permeable material, a non-limiting example, In ₂ 0 ₃ : A transparent conductive film made of Sn and ZnO and a metal film of Au, Pt, Al, and Ni can be used. In addition, a layer made of Ti, Ni, Cr, or the like may be used to improve adhesion between the active layer 20 and each electrode. Meanwhile, the method of forming the source electrode 30, the drain electrode 40, and the gate electrode 60 is not particularly limited as long as it is known in the art.

Permeable material used as the gate insulating film 50 is not specifically limited, but non-limiting examples can be used _{SiO 2, SiO 2, Y 2} 0 3, Al 2 0 3, HfO 2 And at least one of TiO ₂ may be used together. In addition to the oxides, nitrides (eg, Si ₃ N ₄ ), HfN, organics, polyimide (PI), parylene, polyvinylphenol (PVP), poly (methyl methacrylate) (PMMA), and the like may be used. As a method of forming the gate insulating film 50, non-limiting examples include sputtering, pulsed laser deposition, electron beam deposition, spin coating, spraying and inkjet printing (atmospheric pressure).

Meanwhile, although the present invention has been described with reference to a thin film transistor having a top gate structure, the present invention is not limited thereto and may be applied to a thin film transistor having a bottom gate structure. That is, after forming the gate electrode and the gate insulating film on the substrate, the curvature is applied to the substrate on which the gate electrode and the gate insulating film are formed as described above, and after forming the active layer, the curvature of the substrate is removed to apply a compressive stress to the active layer. To manufacture a transistor.

10: substrate
20: active layer
30: source electrode
40: drain electrode
50: gate insulating film
60: gate electrode

Claims (1)

Preparing a substrate having a predetermined curvature and flexibility;
Forming an active layer of an oxide semiconductor on the convex surface of the substrate;
Applying a compressive stress to the active layer by removing curvature of the substrate so that the substrate is horizontal; And
Forming a source electrode, a drain electrode, a gate insulating film, and a gate electrode on the active layer.

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