JP2011158579A - Substrate mounted with thin film transistor, method for manufacturing the same, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a substrate mounted with a thin film transistor, composed of a plastic substrate mounted with a thin film transistor, in which stabilization and high quality of an oxide thin film used as an active layer are achieved. <P>SOLUTION: The method includes at least a step of forming an amorphous oxide thin film 13 as an active layer on or above a plastic substrate 10 and a step of subjecting the amorphous oxide thin film 13 to electromagnetic induction heating. The electromagnetic induction heating step is characterized in that a temperature equal to or higher than the glass transition temperature of the plastic substrate 10 is not applied to the plastic substrate 10 for a given time, and the resistivity of the amorphous oxide thin film 13 is increased and stabilized while keeping the amorphous phase. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thin film transistor mounting substrate, a manufacturing method thereof, and an image display device, and more particularly to a thin film transistor mounting substrate that realizes stabilization and high quality of an amorphous oxide thin film used as an active layer, a manufacturing method thereof, and the like.

  A thin film transistor mounting substrate on which a thin film transistor (TFT) is mounted is used as a driving element substrate such as a liquid crystal display (LCD) and an organic EL display. Thin film transistors include inverted staggered (top gate) and staggered (bottom gate) structural forms, and an amorphous silicon film or a polysilicon film is generally applied as a semiconductor thin film constituting the thin film transistor. Yes. However, although the amorphous silicon semiconductor thin film has stable characteristics, the mobility is small, whereas the polysilicon semiconductor thin film has a high mobility but requires a high temperature (for example, 600 ° C. or higher) heat treatment step.

  Under such circumstances, research and development have been actively conducted on flexible display devices (organic EL displays and electrophoretic displays) using organic EL elements or electrophoretic elements. As a constituent member of a TFT mounting substrate used for a flexible display device, a plastic substrate or a general-purpose glass substrate which is poor in heat resistance but excellent in flexibility has been studied. Since a thin film transistor which is a driving element is directly formed on a substrate constituting a display device, a process temperature in manufacturing the thin film transistor is applied to such a plastic substrate. However, the plastic substrate has poor heat resistance, and a high-temperature heat treatment process that damages the plastic substrate cannot be included in the thin film transistor manufacturing process.

  On the other hand, research on thin film transistors using an oxide thin film as a semiconductor film has been actively conducted in recent years. Patent Document 1 proposes an example in which a polycrystalline thin film of an oxide composed of In, Ga, and Zn (abbreviated as “IGZO”) is used as a semiconductor film of a TFT. In Non-Patent Document 1 and Patent Document 2, IGZO is proposed. An example in which the amorphous thin film is used as a semiconductor film of a TFT has been proposed. TFTs using these IGZO as a semiconductor film can be formed at room temperature and can be formed without damaging the plastic substrate.

  However, a TFT using the IGZO thin film as a semiconductor film has a problem that the threshold voltage changes greatly during continuous energization and lacks stability. In response to this stability problem, Patent Document 3 proposes to increase the stability by covering the IGZO semiconductor thin film with a protective film. On the other hand, Patent Document 4 proposes that the problem of lack of stability can be solved by performing heat treatment on an IGZO semiconductor thin film at 200 ° C. or more and 600 ° C. or less, usually 400 ° C. in an oxidizing gas atmosphere.

K. Nomura et.al., Nature, vol.432, p.488-492 (2004)

JP 2004-103957 A JP 2005-88726 A JP 2007-311404 A JP 2007-73705 A

  However, only by providing the protective film described in Patent Document 3, there is still a change in the threshold voltage during continuous energization, and stability cannot be improved. In addition, since the silicon wafer is used as the substrate in the example of Patent Document 4, heat treatment at 200 ° C. or higher and 600 ° C. or lower (usually 400 ° C.) can be applied, but when using a plastic substrate with poor heat resistance, There is a problem that heat damage to the substrate is large and such means cannot be applied. For example, a polyethylene naphthalate substrate preferably used as a flexible substrate has a glass transition temperature of 150 ° C. or lower.

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a thin film transistor mounting substrate in which a thin film transistor that realizes stabilization and high quality of an oxide thin film used as an active layer is mounted on a plastic substrate. It is in providing the manufacturing method of. Another object of the present invention is to provide a thin film transistor mounting substrate obtained by such a manufacturing method. Still another object of the present invention is to provide an image display device having such a thin film transistor mounting substrate.

  The present inventor conducted electromagnetic induction heating (IH: Induction Heating) of the deposited amorphous oxide thin film in the course of research on the stabilization and high quality of the amorphous oxide thin film without damaging the plastic substrate. The present invention was completed by discovering that a thin film transistor mounting substrate exhibiting high stability and high quality can be obtained.

  That is, the method for manufacturing a thin film transistor mounting substrate according to the present invention includes a step of forming an amorphous oxide thin film serving as an active layer on or above a plastic substrate, and a step of electromagnetically heating the amorphous oxide thin film. And at least the electromagnetic induction heating step controls the plastic substrate to a predetermined resistivity while keeping the amorphous oxide thin film in an amorphous phase without giving the plastic substrate a temperature equal to or higher than the glass transition temperature of the plastic substrate for a certain period of time. It is a process.

  According to the present invention, the amorphous oxide thin film is subjected to electromagnetic induction heating that is controlled to a predetermined resistivity while remaining in the amorphous phase. Control of resistivity by electromagnetic induction heating is based on the fact that amorphous oxide thin film is a semiconductor whose conductivity has decreased to the extent that electromagnetic induction heating is suppressed from “the resistivity of the semiconductor phase that is conductive enough to cause electromagnetic induction heating”. It means that it occurs due to the transition to “phase resistivity”, in other words, due to the transition from “semiconductor close to a conductor with high carrier concentration” to “semiconductor with low carrier concentration”. When the amorphous oxide thin film becomes “resistivity of a semiconductor phase with reduced conductivity (semiconductor phase with a low carrier concentration)”, eddy currents hardly flow through the amorphous oxide thin film, and heat generation is suppressed and temperature is reduced. Decreases and electromagnetic induction heating is substantially terminated. According to the present invention having such characteristics, the resistivity of the amorphous oxide thin film converges to the “resistivity of the semiconductor phase having a low carrier concentration” by which the eddy current does not easily flow by electromagnetically heating the amorphous oxide thin film. Therefore, the semiconductor characteristics are stable and of high quality, and the obtained thin film transistor mounting substrate can be used as a stable and high quality driving element substrate.

  In the electromagnetic induction heating applied in the present invention, a high-frequency current is caused to flow through a heating coil to generate a magnetic flux fluctuation (magnetic field change), and an amorphous oxide thin film is placed in the magnetic flux fluctuation field to vortex the amorphous oxide thin film. An electric current is generated to generate heat. According to this electromagnetic induction heating, the amorphous oxide thin film can be heated even if it is not exposed on the surface. In addition, the thin film transistor mounting substrate has good conductivity, and eddy currents are not generated. Good conductive materials such as gate electrodes and source / drain electrodes have low resistance and no Joule heat. Further, plastic substrates and gate insulating films As described above, since the insulating material has a high resistance and no current flows, no Joule heat is generated, neither of them is heated, and only the amorphous oxide thin film is mainly selectively heated by electromagnetic induction in a short time. Therefore, a plastic substrate having poor heat resistance can be used without any problem without giving the plastic substrate a temperature higher than the glass transition temperature of the plastic substrate for a certain period of time. As a result, a thin film transistor mounting substrate that can be preferably used for a flexible display device can be obtained.

  In a preferred aspect of the method for manufacturing a thin film transistor mounting substrate according to the present invention, in the electromagnetic induction heating step, the amorphous oxide thin film is changed from a conductive semiconductor phase to a semiconductor phase having a predetermined range of resistivity or carrier concentration. It is constituted so that. In this case, when the amorphous oxide thin film reaches a semiconductor phase having a resistivity or carrier concentration within a predetermined range, the temperature of the amorphous oxide thin film decreases.

  According to these inventions, by performing electromagnetic induction heating, the amorphous oxide thin film is changed from a conductive low-resistance semiconductor phase to a semiconductor phase having a predetermined range of resistivity or carrier concentration. Since the eddy current is less likely to flow through the amorphous oxide thin film that has become the semiconductor phase in this manner, heat generation is suppressed, the temperature is lowered, and electromagnetic induction heating is substantially terminated. This causes the amorphous oxide thin film to converge to the resistivity of the semiconductor phase having a low carrier concentration, so that the semiconductor characteristics can be made stable and of high quality.

  A preferable aspect of the method for manufacturing a thin film transistor mounting substrate according to the present invention is configured such that the time when the temperature of the amorphous oxide thin film is lowered is set as the end point of the electromagnetic induction heating step.

  According to the present invention, when the temperature of the amorphous oxide thin film is lowered, the end point of the electromagnetic induction heating process is set as the end point. Therefore, by monitoring the temperature of the amorphous oxide thin film during the electromagnetic induction heating, the amorphous having uniform semiconductor characteristics can be obtained. The time when the oxide thin film is obtained can be certified. As a result, efficient and low-cost electromagnetic induction heating can be performed.

  In order to solve the above problems, a thin film transistor mounting substrate according to the present invention is a thin film transistor mounting substrate having at least a plastic substrate, a gate electrode, a gate insulating film, an active layer, a source electrode, and a drain electrode. Is an amorphous oxide thin film formed by electromagnetic induction heating in which the plastic substrate is not given a temperature higher than the glass transition temperature of the plastic substrate for a certain period of time.

  The amorphous oxide thin film as the active layer is processed by electromagnetic induction heating that does not give the plastic substrate a temperature higher than the glass transition temperature of the plastic substrate for a certain period of time. Since the carrier concentration is stabilized, it can be preferably used as a stable and high-quality drive element substrate. Moreover, electromagnetic induction heating mainly heats only the amorphous oxide thin film and does not give the plastic substrate a temperature above the glass transition temperature of the plastic substrate for a certain period of time, so there is no thermal damage to the plastic substrate having poor heat resistance. As a result, it can be preferably used for a flexible display device.

  A preferable aspect of the thin film transistor mounting substrate according to the present invention is configured such that the amorphous oxide thin film is an InGaZnO-based oxide thin film.

  According to the present invention, as the amorphous oxide thin film, the InGaZnO-based oxide thin film showing the conductor characteristics having the low resistivity and the high carrier concentration in the state before the electromagnetic induction heating is applied. The resistivity of the physical thin film converges to a resistivity that makes eddy currents difficult to flow, that is, “a resistivity of a semiconductor phase having a low carrier concentration”. As a result, the semiconductor characteristics become stable and high quality, and the obtained thin film transistor mounting substrate can be used as a stable and high quality driving element substrate.

  An image display device according to the present invention for solving the above-described problems is characterized in that the thin film transistor mounting substrate according to the present invention is used as an active matrix switching element substrate.

  According to the present invention, the thin film transistor element mounting substrate is provided with an amorphous oxide thin film having high resistivity and high mobility as an active layer, and the plastic substrate is also free from thermal damage. An image display device having a matrix type switching element substrate is obtained.

  According to the method for manufacturing a thin film transistor mounting substrate according to the present invention, the resistivity of the amorphous oxide thin film is reduced by electromagnetic induction heating of the amorphous oxide thin film, which makes it difficult for eddy currents to flow. The semiconductor characteristics are stable and of high quality, and the obtained thin film transistor mounting substrate can be used as a stable and high quality driving element substrate. Moreover, in this thin film transistor mounting substrate, a highly conductive material such as a gate electrode and a source / drain electrode, which has low resistance and does not generate eddy current, is not heated because Joule heat does not occur. Since a high resistance insulating material such as an insulating film does not cause current to flow, Joule heat does not occur. Therefore, only the amorphous oxide thin film is mainly selectively heated by electromagnetic induction in a short time. Therefore, a plastic substrate having poor heat resistance can be used without any problem without giving the plastic substrate a temperature equal to or higher than the glass transition temperature of the plastic substrate for a certain period of time. As a result, a thin film transistor mounting substrate that can be preferably used for a flexible display device can be obtained.

  The thin film transistor mounting substrate according to the present invention has an amorphous oxide thin film in which resistivity and carrier concentration are stabilized, and therefore can be preferably used as a stable and high-quality driving element substrate. Moreover, electromagnetic induction heating mainly heats only the amorphous oxide thin film and does not give the plastic substrate a temperature above the glass transition temperature of the plastic substrate for a certain period of time, so there is no thermal damage to the plastic substrate having poor heat resistance. As a result, it can be preferably used for a flexible display device.

  The image display device according to the present invention is an image display device having a stable and high quality active matrix switching element substrate.

It is explanatory drawing which shows the example of the thin-film transistor element mounting substrate which concerns on the 1st form of this invention, and its manufacturing method. It is explanatory drawing which shows the example of the thin-film transistor element mounting substrate which concerns on the 2nd form of this invention, and its manufacturing method. It is explanatory drawing which shows the example of the thin-film transistor element mounting substrate which concerns on the 3rd form of this invention, and its manufacturing method.

  Hereinafter, the thin film transistor element mounting substrate, the manufacturing method thereof, and the image display device according to the present invention will be described in detail, but the present invention is not limited to the form of the drawings and the following embodiments.

[Thin film transistor element mounting substrate]
As shown in FIGS. 1B, 2B, and 3B, the thin film transistor element mounting substrate 1 (1A to 1C) according to the present invention includes a plastic substrate 10, a gate electrode 15g, and gate insulation. It has at least a film 14, an active layer 13, a source electrode 15s, and a drain electrode 15d. In the present invention, the active layer 13 is an amorphous oxide thin film (hereinafter referred to as the active layer having the same sign as the active layer) formed by electromagnetic induction heating that does not give the plastic substrate 10 a temperature higher than the glass transition temperature of the plastic substrate for a certain period of time. 13 is used).

  The form of the thin film transistor element mounting substrate (hereinafter referred to as “TFT substrate”) having such an active layer 13 is not particularly limited, and the bottom gate bottom of the form (first form) shown in FIG. It may be a contact structure, a bottom gate top contact structure of the form shown in FIG. 2B (second form), or a top of the form shown in FIG. 3B (third form). It may be a gate top contact structure or a top gate bottom contact structure (not shown).

  A bottom gate bottom contact structure TFT substrate 1A according to the first embodiment shown in FIG. 1B includes a plastic substrate 10, a first base film 11 formed on the plastic substrate 10 as necessary, and a first lower film A second base film 12 formed on the base film 11 as necessary, a gate electrode 15g formed on the second base film 12 (or the plastic substrate 10 or the first base film 11), and the gate electrode 15g are covered. Formed on the gate insulating film 14, the source electrode 15 s and the drain electrode 15 d formed on the gate insulating film 14 apart from the portion directly above the central portion of the gate electrode 15 g, and the gate insulating film 14 g. The amorphous electrode is formed so as to contact the source electrode 15s and the drain electrode 15d on both sides and straddle the source electrode 15s and the drain electrode 15d. An oxide film 13, and a protective film 18 formed as necessary to cover their entirety. In the present application, “so as to cover the gate electrode” refers to the embodiment shown in FIG. 1 and is formed on the gate electrode, and the second base film 12 (or plastic substrate 10 or It means that it is also formed on the first base film 11).

  A TFT substrate 1B having a bottom gate top contact structure according to the second mode shown in FIG. 2B includes a plastic substrate 10, a first base film 11 formed on the plastic substrate 10 as necessary, and a first bottom film. A second base film 12 formed on the base film 11 as necessary, a gate electrode 15g formed on the second base film 12 (or the plastic substrate 10 or the first base film 11), and the gate electrode 15g are covered. The gate insulating film 14 thus formed, the amorphous oxide thin film 13 formed on the gate insulating film 14 and immediately above the gate electrode 15g, and the central portion on the amorphous oxide thin film 13 are opened and separated. The source electrode 15s and the drain electrode 15d are formed, and a protective film 18 is formed as necessary so as to cover them.

  A TFT substrate 1C having a top gate top contact structure according to the third embodiment shown in FIG. 3B includes a plastic substrate 10, a first base film 11 formed on the plastic substrate 10 as necessary, and a first bottom film. A second base film 12 formed as necessary on the base film 11 and an amorphous oxide thin film 13 (source side diffusion region) formed on the second base film 12 (or the plastic substrate 10 or the first base film 11). 13s, the channel region 13c and the drain side diffusion region 13d), and the gate insulating film 14g formed mainly on the channel region 13c of the amorphous oxide thin film 13 and the gate insulating film 14g so as to have a contact hole. An insulating film 14 formed on the amorphous oxide thin film 13, a gate electrode 15 g formed on the gate insulating film 14 g, a contour A source electrode 15s and the drain electrode 15d formed on Tohoru, and a protective film 18 formed as needed so as to cover the whole.

  Although not shown, the TFT substrate having a top gate / bottom contact structure includes a plastic substrate (10), a first base film (11) formed on the plastic substrate (10) as necessary, and a first base film. (11) The second base film (12) formed on the second base film (12) and the second base film (12) (or a plastic substrate or the first base film) are formed so as to be spaced apart from each other. The source electrode (15s) and the drain electrode (15d), the insulating layer formed so as to fill the predetermined region between the source electrode (15s) and the drain electrode (15d), and (source electrode-insulating layer-) An amorphous oxide thin film 13 formed on the drain electrode), a gate insulating film (14g) formed on the amorphous oxide thin film 13, and a gate insulating film (14g). And a gate electrode (15 g), and a protective film formed as necessary so as to cover them (18).

  As shown in FIGS. 1 (A), 2 (A), and 3 (A), the amorphous oxide thin film 13 may be one that has been subjected to electromagnetic induction heating immediately after the amorphous oxide thin film 13 is formed. As shown in FIGS. 1B, 2B, and 3B, the protective film 18 may be formed and then heated by electromagnetic induction.

  Hereinafter, the components of the TFT substrate 1 will be described in detail.

(Plastic substrate)
The plastic substrate 10 is an insulative substrate that forms a support substrate for the TFT substrate 1 and is a non-heat resistant substrate having poor heat resistance. In other words, the plastic substrate 10 is a substrate that generally dislikes that a temperature equal to or higher than the glass transition temperature of the plastic substrate 10 is applied for a certain period of time. Specifically, for example, polyethylene naphthalate (glass transition temperature: 120 ° C.), polybutylene terephthalate (75 ° C.), polyethylene terephthalate (75 ° C.), polyphenylene sulfide (90 ° C.), polyether ether ketone (143 ° C.), Polycarbonate (145 ° C), polysulfone (190 ° C), polyarylate (193 ° C), polyethersulfone (225 ° C), polyamide (200 ° C), polyetherimide (215 ° C), polyamideimide (280 ° C), heat Examples thereof include a plastic substrate made of plastic polyimide (280 ° C.) or the like, or a composite substrate thereof. In addition, liquid crystal polymers, fluororesins, and polynorbornene resins are basically included in the plastic substrate 10 in the present application because it is desired to avoid high temperature.

  The plastic substrate may be rigid or may be a thin flexible film having a thickness of about 5 μm to 300 μm. The use of a flexible plastic substrate can be applied to a flexible display device or the like because the TFT substrate 1 can be a flexible substrate.

  Examples of the inorganic substrate include a non-alkali glass substrate that is slightly inferior in heat resistance but inexpensive. Although the thickness of a glass substrate is not specifically limited, Usually, it is about 0.05 mm or more and 3.0 mm or less.

  The present invention is particularly effective when a plastic substrate having a glass transition temperature of less than 200 ° C. is used. When a temperature of 200 ° C. or higher is applied to a plastic substrate having a glass transition temperature of less than 200 ° C. for a certain period of time, the plastic substrate is likely to bend, discolor, or shrink. Therefore, the glass transition temperature is less than 200 ° C. The plastic substrate is a substrate that is disliked that a temperature of 200 ° C. or higher is applied for a certain time. Such a substrate includes most of the plastic substrates described above, and particularly preferably used plastic substrates include polyethersulfone and polyethylene naphthalate. Note that the fixed time varies depending on the glass transition temperature of the plastic substrate, so it cannot be generally stated. For example, in the case of PEN, for example, when it is continuously exposed to an atmosphere of 200 ° C. for about 1 minute, for example, bending occurs. . The glass transition temperature is measured by differential scanning calorimetry (DSC).

(First base film and second base film)
The first base film 11 and the second base film 12 are films formed on the plastic substrate 10 as necessary, and may be formed only in necessary regions or formed on the entire surface according to their functions and purposes. May be. The first base film 11 and the second base film 12 are any materials selected from the group consisting of chromium, titanium, aluminum, silicon, chromium oxide, titanium oxide, aluminum oxide, silicon oxide, silicon nitride, and silicon oxynitride. Formed with. For example, when used as an adhesion film, a metal-based inorganic film made of chromium, titanium, aluminum, silicon, or the like is preferably used. When used as a stress relaxation film or a buffer film (thermal buffer film), chromium oxide, A compound film made of titanium oxide, aluminum oxide, silicon oxide, silicon nitride, silicon oxynitride or the like is preferably used. When used as a barrier film, a compound film made of silicon oxide or silicon oxynitride is preferably used. These films may be provided as a single layer, or two or more layers may be laminated depending on the function and purpose.

  As a preferred example, as shown in FIGS. 1 to 3, a metal-based inorganic film made of chromium, titanium, aluminum, silicon, or the like is formed using the first base film 11 as an adhesion film, and the second base film 12 is formed. As a buffer film, a compound film made of chromium oxide, titanium oxide, aluminum oxide, silicon oxide, silicon nitride, silicon oxynitride, or the like is preferably stacked.

  The thickness of the first base film 11 formed as an adhesion film varies slightly depending on the material constituting the film, but is preferably in the range of about 1 nm to 200 nm, preferably about 3 nm to 50 nm. It is more preferable to be within the range. On the other hand, the thickness when the second underlayer 12 is formed as a buffer film is slightly different depending on the material of the actually formed film, but the thickness is usually in the range of about 100 nm to 1000 nm. In view of film formation time, it is more preferably in the range of about 100 nm to 500 nm.

  The first base film 11 and the second base film 12 can be formed by various methods such as various vapor deposition methods, DC sputtering methods, RF magnetron sputtering methods, and plasma CVD methods. A preferred method according to the material to be used is adopted. Usually, a DC sputtering method, an RF magnetron sputtering method, or the like is preferably used.

(Amorphous oxide thin film)
The amorphous oxide thin film 13 applied in the present invention has a mobility that can be used as an active film (channel film) constituting the TFT substrate 1, and is in an amorphous state (amorphous phase) before and after electromagnetic induction heating. The resistivity increases and stabilizes after the electromagnetic induction heating and before the electromagnetic induction heating. The type is not particularly limited as long as it is an amorphous oxide thin film 13 having such characteristics, and even an amorphous oxide thin film that is currently known may be an amorphous oxide thin film formed by an oxide discovered in the future. It may be. Note that “resistivity is stabilized” means that the variation in resistivity of the amorphous oxide thin film 13 which is an active layer of the TFT formed on the TFT substrate 1 is reduced (for example, within ± 5%). To do.

As an amorphous oxide which comprises the amorphous oxide thin film 13, the amorphous oxide which has InMZnO (M is at least 1 sort (s) among Ga, Al, and Fe) as a main structural element can be mentioned, for example. In particular, an InGaZnO-based amorphous oxide in which M is Ga is preferable. In this case, the ratio of In: Ga: Zn is preferably 1: 1: m (m <6). When Mg is further included, it is preferable that the ratio of In: Ga: Zn _1-x Mg _x is 1: 1: m (m <6) and 0 <x ≦ 1. The composition ratio is measured by a fluorescent X-ray (XRF) apparatus.

Note that an InGaZnO-based amorphous oxide exhibits an amorphous phase in a wide composition range of In, Ga, and Zn. The composition range stably showing the amorphous phase in this ternary system is In _x Ga _y Zn _z O _{(3x / 2 + 3y / 2 + z)} and the ratio x / y is in the range of 0.4 to 1.4, and the ratio It can be expressed such that z / y is in the range of 0.2-12. In addition, crystalline is shown with a composition close to ZnO and a composition close to In ₂ O ₃ .

Amorphous oxides include In _x Ga _1-x oxide (0 ≦ x ≦ 1), In _x Zn _1-x oxide (0.2 ≦ x ≦ 1), In _x Sn _1-x oxide ( Any amorphous oxide selected from 0.8 ≦ x ≦ 1) and In _x (Zn, Sn) _1-x oxide (0.15 ≦ x ≦ 1) may be used.

  In the present invention, an InGaZnO-based (hereinafter abbreviated as “IGZO”) oxide thin film used in Examples described later can be preferably exemplified. Further, this IGZO-based oxide thin film may be provided with Al, Fe, Sn, or the like as a constituent element, if necessary. Since this IGZO-based oxide thin film transmits a visible light and becomes a transparent film or a semi-transparent film, if it is used as a semiconductor film of a TFT for driving a liquid crystal or an organic EL, the semiconductor film is also provided in the opening region. And the optical aperture can be enlarged. As a result, it can be used for a semiconductor film constituting a driving TFT substrate such as a liquid crystal display device, an organic EL display device, and electronic paper. In particular, since this IGZO-based oxide thin film can be formed at room temperature to a low temperature of about 150 ° C., it can be preferably applied to a plastic substrate having a glass transition temperature of less than 200 ° C.

  Whether or not the oxide thin film 13 is amorphous indicates the presence of crystallinity when the oxide thin film to be measured is subjected to X-ray diffraction at a low incident angle of about 0.5 °. It can be confirmed that a clear diffraction peak is not detected, that is, a so-called halo pattern is observed. Since the halo pattern is also observed in a microcrystalline oxide thin film, the amorphous oxide thin film 13 includes such a microcrystalline oxide thin film.

  For example, in the TFT substrate 1A having a bottom gate bottom contact structure shown in FIG. 1, the amorphous oxide thin film 13 is formed on the entire surface after patterning the source / drain electrodes 15s and 15d by a DC sputtering method, an RF magnetron sputtering method, a plasma CVD method. It can be formed by various methods. As the sputtering target, it is preferable to use a sputtering target adjusted so as to obtain a desired film-forming composition under predetermined sputtering conditions. Usually, a sputtering target having the same composition as the target film-forming composition is preferably used. In the TFT substrate 1B having the bottom gate top contact structure shown in FIG. 2, the amorphous oxide thin film 13 can be formed on the gate insulating film 14 by the same method as described above, and the TFT having the top gate top contact structure shown in FIG. In the substrate 1C, the amorphous oxide thin film 13 can be formed on the plastic substrate 10 or on the base film (the first base film 11 or the second base film 12) by the same method as described above.

  The thickness of the amorphous oxide thin film 13 is not generally specified because it is arbitrarily designed depending on the film forming conditions, but it is usually preferably in the range of 10 nm to 150 nm, preferably in the range of 30 nm to 100 nm. More preferably.

The amorphous oxide thin film 13 is formed by electromagnetic induction heating after film formation, and is an amorphous thin film whose resistivity is increased and stabilized by electromagnetic induction heating. Here, “the resistivity increases and stabilizes” means that the resistivity of the amorphous oxide thin film 13 formed on the TFT substrate 1 is in a certain range (range of predetermined variation) in all of them. It means that. At this time, the resistivity in a certain range depends on the type of amorphous oxide film formed, but for example, in the case of an IGZO-based amorphous oxide semiconductor, the resistivity is 10 cm ² / (V · s) or more. A case where the variation is within ± 5% can be exemplified.

  Thus, in the TFT substrate 1, particularly a TFT substrate that functions as a driving device for a large-area display device, the level of mobility of the semiconductor film constituting each TFT is certainly important, but more than that, It is more important that the resistivity of each semiconductor film is within a desired range and that the variation is within a certain variation range within the large area TFT substrate in order to realize stable driving as a drive element. It is. In the present invention, the mobility of the semiconductor film can be improved by electromagnetic induction heating of the amorphous oxide thin film 13 after film formation. However, it is particularly effective that the resistivity of the semiconductor film is a resistance suitable for the semiconductor. The variation is within the range of the rate and the variation can be reduced. Reducing the resistivity value and its variation (so-called stabilization) can suppress changes in the threshold voltage during continuous energization. The range of the resistivity variation can be within ± 10%, preferably within ± 5%, as shown in the examples described later. In the amorphous oxide thin film 13 that has not been subjected to electromagnetic induction heating, the variation in resistivity is about ± 20%, and the variation can be reduced by electromagnetic induction heating. The reason for this behavior is thought to be that some changes have been made to the amorphous structure due to electromagnetic induction heating, and some of these data are available but not clear at this time. However, at least as a result, a result with good reproducibility (stabilization of resistivity) is obtained. The mobility was measured with a Hall effect measuring device, and the resistivity was measured with a 4-probe method.

  Electromagnetic induction heating (IH: Induction Heating) causes high-frequency current to flow through a heating coil to cause magnetic flux fluctuation (magnetic field change), and places the amorphous oxide thin film 13 in the magnetic flux fluctuation field. An eddy current is generated to generate heat. As an example of electromagnetic induction heating, a planar coil can be arranged on one or both sides so as to face the substrate on which the amorphous oxide thin film 13 is formed, or the substrate on which the amorphous oxide thin film 13 is formed can be passed. Thus, the substrate can be passed through a box around which the coil is wound, and any electromagnetic frequency within a range of, for example, 10 kHz to 150 kHz can be applied to the coil.

Here, the electromagnetic frequency applied to the coil is determined based on the resistivity of the amorphous oxide thin film. For example, the resistivity is 1 × 10 ⁻² to 10 × 10 ⁻² IGZO-based oxide thin film. In this case, the frequency is preferably about 50 kHz or 60 kHz. In the amorphous oxide thin film 13 related to the heating object other than the IGZO amorphous oxide thin film, when the resistivity is low, it is preferable to lower the electromagnetic frequency. In addition, the voltage applied to a coil is the range of 50-150V normally. Since the magnitude of the voltage affects the rate of temperature rise due to Joule heating, it is preferable to lower the voltage if the speed is too high and increase the voltage if the speed is too slow.

  In the TFT substrate having the bottom gate bottom contact structure shown in FIG. 1, the electromagnetic induction heating is performed by applying an amorphous oxide thin film 13 on the entire surface after patterning the source / drain electrodes 15s and 15d, as shown in FIG. It may be immediately after formation, or after patterning the amorphous oxide thin film 13, or as shown in FIG. It may be after the substrate 1A is completed. In the electromagnetic induction heating, if the amorphous oxide thin film 13 exists in the magnetic flux fluctuation field, an eddy current can flow and induction heating can be performed. Therefore, the timing shown in FIG. 1A or the timing shown in FIG.

  2 may be immediately after the amorphous oxide thin film 13 is formed on the entire surface of the gate insulating film 14, as shown in FIG. 2A, or in the bottom gate top contact structure shown in FIG. It may be after the amorphous oxide thin film 13 is patterned, or after the protective film 18 is formed on the entire surface and the TFT substrate 1A is completed as shown in FIG. .

  Further, in the top gate top contact structure shown in FIG. 3, as shown in FIG. 3A, it may be immediately after the amorphous oxide thin film 13 is formed on the entire surface of the second base film 12, or Even after the amorphous oxide thin film 13 has been patterned, or as shown in FIG. 3B, the protective film 18 may be formed on the entire surface to complete the TFT substrate 1A. Good.

  In the present invention, the amorphous oxide thin film 13 is subjected to electromagnetic induction heating that increases the resistivity while maintaining the amorphous phase. The increase in resistivity at this time is caused by the transition of the amorphous oxide thin film 13 from “the resistivity of the semiconductor phase that is conductive enough to cause electromagnetic induction heating” to “the resistivity of the semiconductor phase that has decreased conductivity”. This means that it occurs due to the transition from “high carrier concentration” to “low carrier concentration”.

  At this time, “a semiconductor phase that is conductive enough to cause electromagnetic induction heating” is referred to as a “conductor region”, and a “semiconductor phase with reduced conductivity” is referred to as a “semiconductor region”. Heating can be said to change the resistivity or carrier concentration of the amorphous oxide thin film 13 from the conductor region to the semiconductor region. At this time, when the resistivity or carrier concentration of the amorphous oxide thin film 13 heated by electromagnetic induction reaches the semiconductor region and becomes the resistivity (in a state where the carrier concentration is low), an eddy current is generated in the amorphous oxide thin film 13. It becomes difficult to flow, heat generation is suppressed, the temperature decreases, and a phenomenon that electromagnetic induction heating is substantially terminated occurs.

Here, “the resistivity of the semiconductor phase that is conductive enough to cause electromagnetic induction heating” (referred to as “resistivity A”) is in the range of 10 ⁻⁵ to 10 ⁻¹ Ω · cm, The “resistivity of the semiconductor phase with reduced conductivity” (referred to as “resistivity B”) is in the range of 10 ⁻¹ to 10 ⁶ Ω · cm.

Here, since the range of the resistivity A usually correlates well with the high carrier concentration of the amorphous oxide thin film 13, the carrier concentration is 10 ¹⁷ / cm ³ to 10 ²⁰ / in the range of the resistivity A. It can be said that the range is cm ³ . On the other hand, since the range of the resistivity B usually correlates well with the low carrier concentration of the amorphous oxide thin film 13, the carrier concentration is 10 ¹⁷ / cm ³ to 10 ²⁰ / cm in the range of the resistivity B. It can be said that the range is ³ .

  In the present invention, the time point when the temperature of the amorphous oxide thin film 13 is lowered can be set as the end point of the electromagnetic induction heating. For example, by monitoring the temperature of the amorphous oxide thin film 13 during electromagnetic induction heating, the time when the amorphous oxide thin film 13 showing uniform semiconductor characteristics is obtained can be recognized without excess or deficiency. This is advantageous in that efficient and low-cost electromagnetic induction heating is performed.

  From the above, by performing electromagnetic induction heating on the amorphous oxide thin film 13 such as an IGZO amorphous oxide semiconductor that causes the above phenomenon, an eddy current flows in the resistivity of the amorphous oxide thin film 13. Since it converges to the “resistivity B of the semiconductor phase having a low carrier concentration”, the semiconductor characteristics are stable and of high quality.

(Protective film)
As shown in FIGS. 1B, 2B, and 3B, the protective film 18 is a film that acts to protect the TFTs that constitute the TFT substrate 1. By providing the protective film 18, the operation of the TFT is not affected by the atmosphere (for example, moisture, vacuum, temperature), and an unstable operation due to a change in the atmosphere does not occur. can get. Therefore, the protective film 18 is provided so as to cover the whole after the basic structure of the TFT is formed.

Examples of the material for forming the protective film 18 include metal oxides, metal nitrides, metal carbides, and metal oxynitrides containing at least one metal element. As the metal, silicon, aluminum and the like are preferable. Specifically, examples of the metal oxide include SiO ₂ and Al ₂ O ₃ , and examples of the metal nitride include Si _x N _y and AlN. Examples of the metal carbide include SiC and TiC, and examples of the metal oxynitride include SiON and SiAlON. Since the protective film 18 formed of these materials has high resistance and eddy current does not flow in the magnetic flux fluctuation field, the protective film 18 is not heated when performing electromagnetic induction heating on the amorphous oxide thin film 13.

  Examples of the method for forming the protective film 18 include sputtering, resistance heating vapor deposition, laser vapor deposition, electron beam vapor deposition, and chemical vapor deposition (CVD). The protective film 18 is also preferably formed at a temperature lower than the glass transition temperature (preferably lower than 200 ° C.) that does not cause thermal damage to the plastic substrate 10. The thickness of the protective film 18 is not generally specified because it is arbitrarily designed depending on the film forming conditions, but it is usually preferably in the range of 10 nm to 200 nm, and preferably in the range of 50 nm to 150 nm. Is more preferable.

(Other TFT substrate components)
As a material for forming the gate insulating film 14g shown in FIGS. 1 to 3 and the insulating film 14 shown in FIG. 3, various materials can be used as long as they have a high insulating property, a relatively high dielectric constant, and are suitable as a gate insulating film. Materials can be used. For example, at least one or more of yttrium oxide, aluminum oxide, hafnium oxide, zirconium oxide, titanium oxide, tantalum oxide, niobium oxide, and scandium oxide can be used. In addition, silicon oxides such as silicon oxide, silicon nitride, and silicon oxynitride, nitrides, oxynitrides, and the like can also be preferably exemplified. Moreover, complex oxides, such as barium strontium titanate, may be sufficient. Since the insulating films (14g, 14) formed of these materials have high resistance and no eddy current flows in the magnetic flux fluctuation field, they are not heated when performing electromagnetic induction heating on the amorphous oxide thin film 13.

  Examples of the material for forming the gate electrode 15g include gold, silver, copper, titanium, chromium, cobalt, nickel, aluminum, niobium, tantalum, molybdenum, ITO, and the like. The material for forming the source electrode 15s and the drain electrode 15d is preferably a material that can match the energy level with the amorphous oxide thin film 13, and is made of titanium, gold, chromium, iron, molybdenum, tungsten, copper, ruthenium. , Rhenium, ITO, IZO and the like. In particular, IZO, ITO, and Ti are preferable because they can make good ohmic contact with the semiconductor thin film 13. Since the gate electrode 15g and the source / drain electrodes 15s and 15d formed of these materials have low resistance and no Joule heat is generated, the amorphous oxide thin film 13 is not heated when electromagnetic induction heating is performed.

  In addition, even if it is a component other than the above, the TFT substrate 1 according to the present invention may include other films within the scope of the gist of the present invention.

  As described above, the amorphous oxide thin film 13 that is an active layer is processed by electromagnetic induction heating that does not give the plastic substrate 10 a temperature equal to or higher than the glass transition temperature of the plastic substrate 10 for a certain period of time. Since such an amorphous oxide thin film 13 has a stabilized resistivity and carrier concentration, it can be preferably used as a stable and high-quality drive element substrate. In addition, the electromagnetic induction heating mainly heats only the amorphous oxide thin film 13 and does not give the plastic substrate 10 a temperature higher than the glass transition temperature of the plastic substrate 10 for a certain period of time. There is no damage, and as a result, it can be preferably used for a flexible display device. In the present invention, as the amorphous oxide thin film 13, it is preferable to apply an InGaZnO-based oxide thin film showing semiconductor characteristics having a low resistivity and a high carrier concentration in a state before electromagnetic induction heating. 13 is converged to a resistivity at which eddy current does not easily flow due to electromagnetic induction heating, that is, “a resistivity of a semiconductor phase having a low carrier concentration”, so that the semiconductor characteristics are stable and of high quality. The obtained thin film transistor mounting substrate can be used as a stable and high-quality driving element substrate.

[TFT substrate manufacturing method]
The method of manufacturing a thin film transistor element mounting substrate (TFT substrate) according to the present invention includes a step of forming an amorphous oxide thin film 13 serving as an active layer on or above a plastic substrate 10 and electromagnetic induction of the amorphous oxide thin film 13. And a step of heating. Below, each process is demonstrated.

(Electromagnetic induction heating process)
The electromagnetic induction heating process is a process in which a temperature higher than the glass transition temperature of the plastic substrate is not given to the plastic substrate 10 for a certain period of time, and the resistivity is increased and stabilized while the amorphous oxide thin film 13 remains in an amorphous phase. is there. The conditions for electromagnetic induction heating and the like are as described in the explanation section of the “thin film transistor mounting substrate”. In the electromagnetic induction heating, if the amorphous oxide thin film 13 exists in the magnetic flux fluctuation field, an eddy current flows and induction heating can be performed. Therefore, in any of the structures shown in FIGS. As long as the film is formed, the film may be formed at any timing even after the protective film 18 is formed.

  The resistivity of the amorphous oxide thin film 13 that has undergone this process increases, but the increase in resistivity is due to the fact that the amorphous oxide thin film 13 is “the resistivity of the semiconductor phase that is conductive enough to cause electromagnetic induction heating”. Occurs by transition to “resistivity of semiconductor phase whose conductivity has decreased to such an extent that electromagnetic induction heating is suppressed”, in other words, it occurs by transition from “semiconductor with high carrier concentration” to “semiconductor with low carrier concentration”. It means that. When the amorphous oxide thin film 13 becomes “resistivity of semiconductor phase with reduced conductivity (semiconductor with low carrier concentration)”, eddy currents hardly flow through the amorphous oxide thin film 13 and heat generation is suppressed. The temperature drops and the electromagnetic induction heating is substantially finished. Therefore, in this electromagnetic induction heating process, in the process of performing electromagnetic induction heating, it has an end point at which the heating automatically ends, and the temperature decreases after the end point.

  According to the present invention having such characteristics, the amorphous oxide thin film 13 is heated by electromagnetic induction heating, whereby the resistivity of the amorphous oxide thin film 13 is less likely to flow eddy currents “resistivity of semiconductor phase with low carrier concentration”. Therefore, the semiconductor characteristics are stable and of high quality, and the obtained thin film transistor mounting substrate can be used as a stable and high quality driving element substrate.

  In this electromagnetic induction heating process, a high-frequency current is passed through the heating coil to cause a magnetic flux fluctuation (magnetic field change), and an eddy current is generated in the amorphous oxide thin film 13 by placing the amorphous oxide thin film 13 in the magnetic flux fluctuation field. The electromagnetic induction heating allows heating even if the amorphous oxide thin film 13 is not exposed on the surface. In addition, the TFT substrate 1 has good conductivity and does not generate eddy current, and the highly conductive materials such as the gate electrode 15g, the source electrode 15s, and the drain electrode 15d have low resistance and do not generate Joule heat. In addition, since the insulating material such as the gate insulating film 14g has high resistance and no current flows, no Joule heat is generated, neither is heated, and only the amorphous oxide thin film 13 is mainly selectively and electromagnetically induced in a short time. Heated. Therefore, the plastic substrate 10 is not given a temperature higher than the glass transition temperature of the plastic substrate 10 for a certain period of time, and a plastic substrate having a glass transition temperature of less than 200 ° C. can be used without any problem.

(Formation process of amorphous oxide thin film)
Prior to the electromagnetic induction heating step, a step of forming the amorphous oxide thin film 13 is provided. The step of forming the amorphous oxide thin film 13 is a step of forming the amorphous oxide thin film 13 that becomes an active layer on or above the plastic substrate 10 having a glass transition temperature of less than 200 ° C. Here, the reason why the amorphous oxide thin film 13 is set on or above the plastic substrate 10 is that the amorphous oxide thin film 13 may be directly formed on the plastic substrate 10. Normally, as shown in FIGS. 1 to 3, the first base film 11 or the second base film 12 is formed on the plastic substrate 10, and the amorphous oxide thin film 13 is formed thereon. desirable.

(Other processes)
The manufacturing method of the TFT substrate according to the present invention includes a process of forming each film shown in FIGS. For example, the process of forming the first base film 11, the process of forming the second base film 12, the process of forming the gate electrode 15g, the process of forming the gate insulating film 14g, the process of forming the source electrode 15s and the drain electrode 15d, A forming process (see FIG. 3), a patterning process, a cleaning process, an ion implantation process, a forming process of the protective film 18 and the like are arbitrarily included according to the structure of the TFT substrate to be manufactured. Each of these steps is performed using the constituent materials and the film forming means described in the above “TFT substrate” column.

  As described above, according to the manufacturing method of the TFT substrate 1 according to the present invention, the amorphous oxide thin film 13 is electromagnetically heated to reduce the resistivity of the amorphous oxide thin film 13 so that an eddy current hardly flows. Since it can converge to the “resistivity of the semiconductor phase having a low carrier concentration”, the semiconductor characteristics become stable and high quality, and the obtained thin film transistor mounting substrate can be used as a stable and high quality driving element substrate. Moreover, in this thin film transistor mounting substrate, a highly conductive material such as a gate electrode and a source / drain electrode, which has low resistance and does not generate eddy current, is not heated because Joule heat does not occur. A high resistance insulating material such as an insulating film does not generate Joule heat because no current flows, and therefore only the amorphous oxide thin film 13 is mainly selectively electromagnetically heated in a short time. Therefore, a plastic substrate having poor heat resistance can be used without any problem without giving the plastic substrate a temperature equal to or higher than the glass transition temperature of the plastic substrate for a certain period of time. As a result, a thin film transistor mounting substrate that can be preferably used for a flexible display device can be obtained.

[Image display device]
In the image display device according to the present invention, the above-described thin film transistor mounting substrate according to the present invention is used as an active matrix switching element substrate such as a liquid crystal display device, an organic EL light emitting display device, and electronic paper. If an organic EL light-emitting display device is described as an image display device of the present invention, it has a number of TFT substrates 1 according to the present invention arranged in a matrix, for example, a gate bus line of a gate electrode 15g and a source electrode 15s The source bus line extends vertically and horizontally, and an output element is connected to the drain electrode 15d of each TFT. This output element is an organic EL element, and is composed of an equivalent circuit composed of a resistor and a capacitor. The area | region for every output element comprises the pixel of an organic electroluminescent light emission display apparatus.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[Example 1]
(Production of TFT substrate)
As an example, a TFT substrate in which a plurality of (72 pieces) TFTs having a bottom gate bottom contact structure TFT shown in FIG. 1 were formed on a plastic substrate was manufactured. First, polyethylene naphthalate (PEN) having a thickness of 100 μm and a glass transition temperature of 150 ° C. is prepared as a plastic substrate 10, and a chromium film (adhesion film) having a thickness of 5 nm is formed on the entire surface of the plastic substrate 10. 11, a silicon oxide film (buffer film) having a thickness of 300 nm was formed on the entire surface of the first base film 11 as a second base film 12 by a sputtering method. Next, after depositing an aluminum film having a thickness of 200 nm as a gate electrode film on the entire surface of the second base film 12, a resist pattern is formed by photolithography and then wet-etched with a phosphoric acid solution to form the aluminum film into a predetermined pattern. Patterning was performed to form a gate electrode 15g. Next, silicon oxide having a thickness of 100 nm was formed as a gate insulating film 14 on the entire surface so as to cover the gate electrode 15g. This gate insulating film 14 is applied to an 8-inch SiO ₂ target using an RF magnetron sputtering apparatus. Electric power: 1.0 kW (= 3 W / cm ² ), pressure: 1.0 Pa, gas: argon + O ₂ (50%) The film was formed under the following film forming conditions. Next, after depositing an aluminum film having a thickness of 200 nm on the entire surface of the gate insulating film 14 to form the source electrode 15s and the drain electrode 15d, a resist pattern is formed by photolithography, and then wet-etched with a phosphoric acid solution. The film was patterned into a predetermined pattern to form a source electrode 15s and a drain electrode 15d. At this time, the source electrode 15s and the drain electrode 15d were formed on the gate insulating film 14 so as to have a pattern apart from other than just above the central portion of the gate electrode 15g (see FIG. 1).

Next, an InGaZnO amorphous oxide thin film 13 (InGaZnO ₄ ) having an In: Ga: Zn ratio of 1: 1: 1 is formed on the entire surface so as to cover the source electrode 15s and the drain electrode 15d. did. The amorphous oxide thin film 13 was formed by using an RF magnetron sputtering apparatus at room temperature (25 ° C.) and Ar: O ₂ of 30:50, 8 inches of InGaZnO (In: Ga: Zn = 1: 1: 1). ) A target was used (see FIG. 1A). Next, this amorphous oxide thin film 13 was heated by electromagnetic induction. As shown in Table 1, the electromagnetic induction heating was performed under conditions of 60 kHz and 10 minutes. After a resist pattern was formed on the amorphous oxide thin film 13 by photolithography, the amorphous oxide thin film 13 was patterned by wet etching with an oxalic acid solution to form an amorphous oxide thin film 13 having a predetermined pattern. The amorphous oxide thin film 13 thus obtained is formed on the gate insulating film 14g so as to contact the source electrode 15s and the drain electrode 15d on both sides and straddle the source electrode 15s and the drain electrode 15d. Finally, silicon oxide having a thickness of 20 nm was formed as a protective film 18 by RF magnetron sputtering so as to cover the entire surface. Thus, a TFT substrate 1 according to Example 1 was manufactured (see FIG. 1B).

[Comparative Example 1]
A TFT substrate of Comparative Example 1 was produced in the same manner as in Example 1 except that annealing was performed at 200 ° C. for 60 minutes in an air atmosphere instead of performing electromagnetic induction heating. Note that annealing was performed after the protective film 18 was formed.

[Comparative Example 2]
A TFT substrate of Comparative Example 2 was fabricated in the same manner as in Example 1 except that annealing was performed in an air atmosphere at 300 ° C. for 60 minutes instead of performing electromagnetic induction heating. Note that annealing was performed after the protective film 18 was formed.

[Characteristic evaluation and results]
The following characteristics were evaluated for the obtained TFT substrate. The results are shown in Table 1. In Table 1, “Before” represents before electromagnetic induction heating or before annealing, and “After” represents after electromagnetic induction heating or after annealing.

(Crystal structure)
The crystal structure of the IGZO oxide thin film before and after electromagnetic induction heating was measured with an X-ray diffraction apparatus (manufactured by Rigaku Corporation, apparatus name: RINT-2500). X-ray diffraction measurement was performed under the conditions of Cu-Kα characteristic X-ray, scan axis 2θ, and incident angle of 0.5 °. In Table 1, “a” represents an amorphous phase, and “p” represents a crystalline phase. In Example 1 and Comparative Example 1, halo was observed before and after heating, and it was confirmed that the crystal structure was an amorphous phase. On the other hand, in Comparative Example 2, a crystalline peak was observed after heating, and it was confirmed that the crystal structure was a crystalline phase.

(Resistivity)
The resistivity (Ω · cm) of the IGZO oxide thin film before and after electromagnetic induction heating was measured using a 4-probe method measuring device. Before the electromagnetic induction heating, it was 5.7 × 10 ⁻² Ω · cm, but after the electromagnetic induction heating, as shown in Table 1, Example 1 had the highest value.

(Carrier concentration)
Hall measurement of the TFT substrate was performed before and after electromagnetic induction heating, and the carrier concentration (cm ² / V / s) was measured. For the measurement, a resistivity / hall measurement system device manufactured by Toyo Technica Co., Ltd. was used. Before electromagnetic induction heating, it was 4.0 × 10 ¹⁸ cm ² / V / s. However, after electromagnetic induction heating, as shown in Table 1, Example 1 and Comparative Example 2 had a lower carrier concentration. .

(ON / OFF measurement)
With respect to the obtained TFT substrate, the ON / OFF characteristics of the drain current were evaluated. Measurement is performed using a semiconductor parameter analyzer (Agilent Technology Co., Ltd., Model 4156C), the TFT transfer characteristics are evaluated, the drain current ON / OFF characteristics are graphed, and the drain current digit at ON and OFF The number difference was evaluated. The ON / OFF ratio before electromagnetic induction heating was 0 digit, but after electromagnetic induction heating, as shown in Table 1, Example 1 and Comparative Example 2 had an ON / OFF ratio of 7 digits.

(Appearance evaluation of plastic substrate)
The appearance and the bending of the plastic substrate (PEN) constituting the obtained TFT substrate were observed. In Table 1, “◯” indicates a case where there is no deflection or discoloration, and “X” indicates a case where there is deflection or discoloration. In Example 1 and Comparative Example 1, no adverse effects such as bending or discoloration were observed, but in Comparative Example 2, the appearance was inferior.

  As can be seen from the results of Examples in Table 1, in Example 1, even when a PEN film having a glass transition temperature of 150 ° C. is used, the amorphous IGZO oxide thin film 13 is subjected to electromagnetic induction heating under predetermined conditions. It was possible to increase the resistivity (at the same time decrease the carrier concentration). The IGZO oxide thin film 13 subjected to electromagnetic induction heating was able to increase the resistivity while maintaining the amorphous phase. And the eddy current did not flow easily through the amorphous oxide thin film 13, the heat generation was suppressed, the temperature was lowered, and the electromagnetic induction heating could be automatically terminated. On the other hand, in Comparative Example 1 of Table 1, damage to the plastic substrate did not occur, but it was insufficient to increase the ON / OFF ratio. In Comparative Example 2, the ON / OFF ratio increased, but the plastic substrate was damaged by the high temperature (300 ° C.) treatment.

1, 1A, 1B, 1C TFT substrate 10 Plastic substrate 11 First underlayer 12 Second underlayer 13 Amorphous oxide thin film (active layer)
13s Source side diffusion region 13c Channel region 13d Drain side diffusion region 14 Insulating film 14g Gate insulating film 15s Source electrode 15g Gate electrode 15d Drain electrode 18 Protective film

Claims (7)

At least a step of forming an amorphous oxide thin film to be an active layer on or above a plastic substrate, and electromagnetic induction heating of the amorphous oxide thin film,
The electromagnetic induction heating step is a step in which the plastic substrate is not given a temperature higher than the glass transition temperature of the plastic substrate for a certain period of time, and the amorphous oxide thin film is controlled to a predetermined resistivity while remaining in an amorphous phase. A method of manufacturing a thin film transistor-mounted substrate, characterized by:   2. The method for manufacturing a thin film transistor-mounted substrate according to claim 1, wherein in the electromagnetic induction heating step, the amorphous oxide thin film is changed from a conductive semiconductor phase to a semiconductor phase having a predetermined range of resistivity or carrier concentration.   The method for manufacturing a thin film transistor-mounted substrate according to claim 2, wherein when the amorphous oxide thin film reaches a semiconductor phase having a resistivity or carrier concentration in a predetermined range, the temperature of the amorphous oxide thin film decreases.   The manufacturing method of the thin-film transistor mounting substrate of Claim 3 which makes the time of the temperature of the said amorphous oxide thin film the end point of the said electromagnetic induction heating process.   In a thin film transistor mounting substrate having at least a plastic substrate, a gate electrode, a gate insulating film, an active layer, a source electrode, and a drain electrode, the active layer has a glass transition temperature equal to or higher than the glass transition temperature of the plastic substrate. A thin film transistor mounting substrate characterized by being an amorphous oxide thin film processed by electromagnetic induction heating without applying a temperature for a certain period of time.   The thin film transistor mounting substrate according to claim 5, wherein the amorphous oxide thin film is an InGaZnO-based oxide thin film.   7. An image display device, wherein the thin film transistor mounting substrate according to claim 5 is used as an active matrix switching element substrate.

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