JP5857432B2 - Thin film transistor manufacturing method - Google Patents

Description

  The present invention relates to a thin film transistor and a method for manufacturing the same. More specifically, an inverted staggered thin film transistor in which a semiconductor film is formed of an oxide that can be formed at low temperature, and a thin film transistor in which a protective film of the thin film transistor is formed of an oxide semiconductor material to form a channel protective film or an ultraviolet light shielding film, and It relates to the manufacturing method.

  A thin film transistor substrate on which a thin film transistor (TFT) is mounted is used as a drive element substrate for a display device such as a liquid crystal display or an organic EL display. Thin film transistors include structural forms such as an inverted staggered type (bottom gate) and a forward staggered type (top gate), and an amorphous silicon semiconductor film or a polysilicon semiconductor film is generally used as a semiconductor film constituting the thin film transistor. Has been applied. However, although the amorphous silicon semiconductor film has stable characteristics but has low mobility, the polysilicon semiconductor film requires high temperature (for example, 600 ° C. or higher) heat treatment process although it has high mobility.

  In recent years, research on thin film transistors using oxide semiconductor films has been actively conducted. 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 thin film transistor. 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 thin film transistor has been proposed. Thin film transistors using these IGZO as semiconductor films can be formed at low temperatures at room temperature, and can be formed without causing thermal damage to non-heat resistant substrates such as plastic substrates.

  The above-described IGZO-based oxide semiconductor has attracted attention in recent years because it has a relatively high mobility despite being an amorphous material formed at a low temperature. In addition, an IGZO-based oxide semiconductor is a transparent material having a high transmittance for visible light, and has a good electrical property even when a conventionally known transparent conductive material such as ITO is used as a gate electrode, a source electrode, or a drain electrode. Since transparent contact characteristics can be obtained, a transparent thin film transistor using only a transparent material has been studied.

Thin film transistors include an inverted staggered structure and a forward staggered structure. In the inverted staggered thin film transistor, a protective film is provided over the semiconductor film in order to protect the channel region of the semiconductor film. For example, in Patent Document 5, a SiO ₂ film or a SiO _x N _y film is provided as a protective film on a semiconductor film. In Patent Document 6, a protective film made of an organic-inorganic composite compound such as a silane compound or an organic acid is provided on the semiconductor film.

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

JP 2004-103957 A JP 2005-88726 A JP 2007-220816 A JP 2007-259883 A JP 2008-53356 A JP 2007-158146 A

However, protective films such as SiO ₂ films and SiO _x N _y films, and protective films made of organic-inorganic composite compounds and organic acids are inferior in stability to oxygen and water vapor when exposed to the atmosphere, ultraviolet rays, etc. There is a possibility that the characteristics of the semiconductor film in the channel region to be protected are deteriorated. In particular, it is expected that the characteristics of the semiconductor film deteriorate when used for a long time. Such characteristic deterioration may impair reliability as a thin film transistor.

  The present invention has been made to solve the above-described problems, and an object of the present invention is an inverted staggered thin film transistor in which a semiconductor film is formed of an oxide that can be formed at a low temperature, and the protection formed on the semiconductor film. It is an object of the present invention to provide a thin film transistor and a method for manufacturing the same, in which the light resistance against ultraviolet rays and the environmental stability of the film are improved.

  In the process of examining the characteristics variation of a thin film transistor with respect to light, particularly ultraviolet light, and the property variation of the thin film transistor with respect to the environment (oxygen or water vapor), the present inventor used an IGZO oxide semiconductor as an inverted staggered thin film transistor. The present invention has been completed by finding that it is effective as a channel protective film or an ultraviolet light-shielding film by using it as a protective film in addition to the semiconductor film to be formed.

  A thin film transistor according to a first aspect of the present invention for solving the above-described problem is formed by patterning a gate electrode patterned on a substrate, a gate insulating film covering the gate electrode, and the gate insulating film A bottom gate top having an oxide semiconductor film, a source electrode and a drain electrode patterned on the oxide semiconductor film, and a protective film covering at least the oxide semiconductor film exposed between the source electrode and the drain electrode A thin film transistor having a contact structure, wherein the protective film is formed of an oxide semiconductor material.

  A thin film transistor according to a second aspect of the present invention for solving the above-described problem is formed by patterning a gate electrode patterned on a substrate, a gate insulating film covering the gate electrode, and the gate insulating film A bottom having a source electrode and a drain electrode, an oxide semiconductor film patterned so as to cover at least the gate insulating film exposed between the source electrode and the drain electrode, and a protective film covering at least the oxide semiconductor film A thin film transistor having a gate bottom contact structure, wherein the protective film is made of an oxide semiconductor material.

According to the invention according to the first and second aspects, the protective film constituting the thin film transistor is formed of an oxide semiconductor material. Protective film made of the oxide semiconductor material has a good optical transparency in the visible light region, whereas, since the ultraviolet region having a good light-shielding properties, SiO ₂ film or an organic inorganic is a conventional protective film Degradation of thin film transistor characteristics (that is, semiconductor characteristics) can be effectively prevented as compared with a composite compound film. In particular, the protective film prevents deterioration of the semiconductor characteristics against ultraviolet light and improves the atmospheric stability of the semiconductor characteristics against water vapor and oxygen gas, so that the thin film transistor provided with the protective layer has excellent long-term reliability. Become. Such a protective film covers at least the oxide semiconductor film exposed between the source electrode and the drain electrode (invention according to the first aspect) or at least covers the oxide semiconductor film exposed as the uppermost layer (according to the second aspect). (Invention) Therefore, it can suppress that an oxide semiconductor film deteriorates when it exposes to an ultraviolet-ray or air | atmosphere atmosphere. Furthermore, according to the present invention, since the protective film can be formed using the same oxide semiconductor material as that of the oxide semiconductor film, a thin film transistor that realizes cost can be provided.

  In the thin film transistor according to the present invention, the oxide semiconductor film and the protective film are preferably made of an amorphous oxide containing InMZnO (M is at least one of Ga, Sn, Al, and Fe).

  According to the present invention, since the protective film is made of an amorphous oxide containing InMZnO, it exhibits good light transmittance particularly in the visible light region and good light shielding property in the ultraviolet light region, so that the thin film transistor characteristics (semiconductor characteristics) Can be more effectively prevented. In particular, an InGaZnO-based amorphous oxide in which M is Ga is preferable.

  A method of manufacturing a thin film transistor according to a first aspect of the present invention for solving the above problems includes a step of patterning a gate electrode on a substrate, a step of forming a gate insulating film covering the gate electrode, and the gate A step of patterning an oxide semiconductor film on the insulating film; a step of patterning a source electrode and a drain electrode on the oxide semiconductor film; and the oxide semiconductor film exposed between the source electrode and the drain electrode. And a step of forming a protective film with an oxide semiconductor material so as to cover at least.

  A method of manufacturing a thin film transistor according to a second aspect of the present invention includes a step of patterning a gate electrode on a substrate, a step of forming a gate insulating film covering the gate electrode, a source electrode and a gate electrode on the gate insulating film Patterning a drain electrode, patterning an oxide semiconductor film covering at least the gate insulating film exposed between the source electrode and the drain electrode, and an oxide covering at least the oxide semiconductor film And a step of forming a protective film with a semiconductor material.

According to the invention according to the first and second aspects, the protective film constituting the thin film transistor is formed of an oxide semiconductor material. This protective film made of an oxide semiconductor material has good light transmittance in the visible light region, while it has good light shielding properties in the ultraviolet light region, so the manufactured thin film transistor is a conventional protective film. Compared with a thin film transistor in which a SiO ₂ film or an organic-inorganic composite compound film is provided as a protective film, deterioration of thin film transistor characteristics (semiconductor characteristics) can be effectively prevented. In particular, the protective layer prevents deterioration of the semiconductor characteristics against ultraviolet light and improves the atmospheric stability of the semiconductor characteristics of the oxide semiconductor film against water vapor and oxygen gas, so that the thin film transistor provided with the protective film has long-term reliability. It will be excellent. In the method for manufacturing a thin film transistor according to the present invention, such a protective film covers at least the oxide semiconductor film exposed between the source electrode and the drain electrode (the invention according to the first aspect) or the oxide semiconductor film exposed as the uppermost layer. Since the oxide semiconductor film is exposed to ultraviolet rays or an air atmosphere, it is possible to suppress deterioration in characteristics. Furthermore, according to the present invention, the protective film can be formed using the same oxide semiconductor material as that of the oxide semiconductor film, so that a thin film transistor with low cost can be provided.

  In the method of manufacturing a thin film transistor according to the present invention, it is preferable that the oxide semiconductor film and the protective film are made of an amorphous oxide containing InMZnO (M is at least one of Ga, Sn, Al, and Fe).

  In the method for manufacturing a thin film transistor according to the present invention, the oxide semiconductor film forming step is preferably a step of forming an oxide semiconductor film by an RF sputtering method in an oxygen gas atmosphere not containing argon.

  According to this invention, since the oxide semiconductor film is formed by RF sputtering in an oxygen gas atmosphere not containing argon, oxygen vacancies in the obtained oxide semiconductor film can be reduced. As a result, an insulating oxide semiconductor film having a low carrier concentration can be obtained. Therefore, a protective film is formed by RF sputtering to increase the carrier concentration of the oxide semiconductor film and adjust its semiconductor characteristics. can do.

  In this case, the protective film forming step is preferably a step of forming the protective film by RF sputtering in an oxygen gas atmosphere not containing argon.

According to the present invention, the protective film is formed by the RF sputtering method in an oxygen gas atmosphere not containing argon, similarly to the oxide semiconductor film described above, so that another film forming chamber or another gas atmosphere is used. Therefore, it is not necessary to form a film at the same time, and the cost can be reduced. Further, at the time of RF sputtering for forming the protective film, the carrier concentration of the oxide semiconductor film can be increased to shift to semiconductor characteristics. In particular, the carrier concentration of the oxide semiconductor film in which the protective film is preferably formed by an RF sputtering method is less than 10 ¹⁵ ions / cm ² .

  In the method for manufacturing a thin film transistor according to the present invention, it is preferable that the step of forming the oxide semiconductor film is a step of forming an oxide semiconductor film by an RF sputtering method in an oxygen gas atmosphere containing argon.

  According to this invention, since the oxide semiconductor film is formed by the RF sputtering method in an oxygen gas atmosphere containing argon, the obtained oxide semiconductor film has many oxygen vacancies. As a result, the obtained oxide semiconductor film becomes an oxide semiconductor film having a carrier concentration suitable for the active layer.

  In this case, the protective film forming step is preferably a step of forming the protective film by a DC sputtering method in an oxygen gas atmosphere not containing argon.

According to the present invention, since the DC sputtering method for forming the protective film in an oxygen gas atmosphere not containing argon is applied, the carrier concentration of the oxide semiconductor film is not significantly affected during the DC sputtering. Note that the carrier concentration of the oxide semiconductor film in which the protective film is preferably formed by a DC sputtering method is 10 ¹⁵ ion / cm ² or more.

According to the thin film transistor and the method for manufacturing the same according to the present invention, the protective film is provided with an oxide semiconductor material having good light transmittance in the visible light region and good light shielding property in the ultraviolet light region. Therefore, the obtained thin film transistor can effectively prevent deterioration of thin film transistor characteristics (semiconductor characteristics) as compared with a thin film transistor in which a conventional protective film such as a SiO ₂ film or an organic-inorganic composite compound film is provided as a protective film. In particular, the protective film prevents deterioration of the semiconductor characteristics against ultraviolet light and improves the atmospheric stability of the semiconductor characteristics against water vapor and oxygen gas, so that the thin film transistor provided with the protective film has excellent long-term reliability. Become. Furthermore, according to the present invention, the protective film can be formed using the same oxide semiconductor material as that of the oxide semiconductor film, so that a thin film transistor with low cost can be provided.

  According to the thin film transistor manufacturing method of the present invention, when an oxide semiconductor film is formed by RF sputtering in an oxygen gas atmosphere not containing argon to form an oxide semiconductor film with few oxygen vacancies. An insulating oxide semiconductor film having a low carrier concentration can be obtained. At this time, the protective film is formed by an RF sputtering method in an oxygen gas atmosphere that does not contain argon, like the oxide semiconductor film, so that a separate film formation chamber is used, or a film is formed in another gas atmosphere. This eliminates the need to do so and realizes cost reduction. Further, at the time of RF sputtering for forming the protective film, the carrier concentration of the oxide semiconductor film can be increased to shift to semiconductor characteristics.

  In addition, according to the method for manufacturing a thin film transistor according to the present invention, the oxide semiconductor film is formed by RF sputtering in an oxygen gas atmosphere containing argon, so that the oxide semiconductor film having many oxygen vacancies is formed. Thus, an oxide semiconductor film suitable for the active layer can be obtained. At this time, since the protective film is formed by a DC sputtering method in an oxygen gas atmosphere not containing argon, an oxide suitable for an active layer without changing much the carrier concentration of the oxide semiconductor film during the DC sputtering. It can be a semiconductor film.

It is typical sectional drawing which shows an example of the thin-film transistor which concerns on this invention. It is typical sectional drawing which shows another example of the thin-film transistor which concerns on this invention. It is typical sectional drawing which shows another example of the thin-film transistor which concerns on this invention. It is typical explanatory drawing which shows each process of the manufacturing method of the thin-film transistor which concerns on this invention. It is a graph which shows the wavelength dependence of the transmittance | permeability of the amorphous oxide (a-IGZO) applied by this invention.

  Hereinafter, a thin film transistor and a manufacturing method thereof according to the present invention will be described in detail with reference to the drawings. The present invention can be modified in various ways as long as it has the technical features, and is not limited to the embodiments specifically shown below.

  The present invention relates to an inverted staggered thin film transistor, and more specifically, to a thin film transistor 10A, 10B having a bottom gate top contact structure or a thin film transistor 10C having a bottom gate bottom contact structure, as shown in FIGS. In the following description, an inverted staggered thin film transistor may be represented by reference numeral 10. Hereinafter, the structure of the thin film transistor according to the present invention will be described with reference to FIGS. 1 to 3, and the method for manufacturing the thin film transistor will be described with reference to FIG.

  As shown in FIGS. 1 to 3, the thin film transistor 10 according to the present invention includes a gate electrode 2, a gate insulating film 3, an oxide semiconductor film 4, a source electrode 6 </ b> S and a drain electrode 6 </ b> D, and a protective film 7 on a substrate 1. Is an inverted staggered thin film transistor.

  Among these, the bottom gate top contact thin film transistors 10A and 10B include a gate electrode 2 patterned on the substrate 1, a gate insulating film 3 covering the gate electrode 2, and a gate, as shown in FIGS. Oxide semiconductor film 4 patterned on insulating film 3, source electrode 6S and drain electrode 6D patterned on oxide semiconductor film 4, and oxide semiconductor exposed between source electrode 6S and drain electrode 6D A thin film transistor 10C having a bottom gate / bottom contact structure covers at least the gate electrode 2 patterned on the substrate 1 and the gate electrode 2 as shown in FIG. Gate insulating film 3, source electrode 6S and drain electrode 6D patterned on gate insulating film 3, and source electrode And S and the drain electrode 6D between the oxide semiconductor film 4 is patterned to cover at least the gate insulating film 3 exposed to, an oxide semiconductor film 4 is one having at least a covering protective film '. A feature of the present invention is that the protective film 7 is formed of an oxide semiconductor material, and covers the oxide semiconductor film 4 ′ exposed between the source electrode 6S and the drain electrode 6D (bottom gate top contact). Structure) or covering the oxide semiconductor film 4 exposed as the uppermost layer (bottom gate bottom contact structure) and covering the source electrode 6S and the drain electrode 6D.

  In the present invention, “above” means that it is provided directly on itself, and when it is not provided directly, it is referred to as “above”. In addition, “covering” means that it is provided directly on itself and around it. The “same material” means that the materials at the time of film formation are the same.

  In the manufacturing method of the inverted staggered thin film transistor 10 having such a configuration, the inverted staggered structure is the thin film transistors 10A and 10B having the bottom gate top contact structure shown in FIGS. 1 and 2, or the bottom gate bottom contact structure shown in FIG. The thin film transistor 10C is slightly different.

  Specifically, the method of manufacturing the thin film transistors 10A and 10B having the bottom gate top contact structure includes a step of patterning the gate electrode 2 on the substrate 1, a step of forming the gate insulating film 3 covering the gate electrode 2, and a gate. A step of patterning the oxide semiconductor film 4 on the insulating film 3, a step of patterning the source electrode 6S and the drain electrode 6D on the oxide semiconductor film 4, and an oxidation exposed between the source electrode 6S and the drain electrode 6D. Forming a protective film 7 with an oxide semiconductor material so as to cover at least the physical semiconductor film 4 ′ (exposed passivation film 5 ′ in FIG. 2). In the case of the bottom gate top contact structure, as shown in FIG. 2 for the purpose of preventing the oxide semiconductor film 4 from being damaged when the source electrode 6S and the drain electrode 6D are provided on the oxide semiconductor film 4. As described above, the passivation film 5 may be provided over the oxide semiconductor film 4.

  On the other hand, the method of manufacturing the thin film transistor 10C having the bottom gate bottom contact structure includes a step of patterning the gate electrode 2 on the substrate 1, a step of forming the gate insulating film 3 covering the gate electrode 2, and a step of forming the gate electrode 2 on the gate insulating film 3. A step of patterning the source electrode 6S and the drain electrode 6D, and at least covering the gate insulating film 3 exposed between the source electrode 6S and the drain electrode 6D, and patterning the oxide semiconductor film 4 also on the source electrode 6S and the drain electrode 6D Forming the protective film 7 with an oxide semiconductor material so as to cover at least the oxide semiconductor film 6.

  In the present invention, “pattern formation” means any plane suitable for using the gate electrode 2, the gate insulating film 3, the oxide semiconductor film 4, the source electrode 6 S, the drain electrode 6 D, and the like as components of the thin film transistor 10. It means to form in a visual shape, and can be paraphrased as “patterning” or “forming with a predetermined pattern”. In the present invention, when “predetermined pattern” is used, components such as the gate electrode 2, the gate insulating film 3, the oxide semiconductor film 4, the source electrode 6 </ b> S, and the drain electrode 6 </ b> D are used as components of the thin film transistor 10. It means an arbitrary plan view shape suitable for use.

  Hereinafter, each component of the thin film transistor and the manufacturing method thereof according to the present invention will be described in detail.

(substrate)
The kind and structure of the board | substrate 1 are not specifically limited, A flexible material, a hard material, etc. are selected according to a use. The substrate 1 may or may not be transparent. Examples of the transparent substrate material include glass, quartz, polyethylene, polypropylene, polyethylene terephthalate, polymethacrylate, polymethyl methacrylate, polymethyl acrylate, polyester, polycarbonate, and the like. Usually, a glass substrate with ITO or a plastic substrate with ITO, which is a transparent electrode, is preferably used. Note that a glass substrate, a plastic substrate, or the like on which a metal film or a transparent conductive film is formed may be used.

  Note that the definition of transparent differs depending on the use of a thin film integrated circuit device using a thin film transistor. However, if one standard is shown, (i) when judging by reflectance, a visible wavelength of 350 nm to 650 nm is used. In the optical region, it is preferable in terms of transparency that the refractive index of each film is about 2 or less and the difference in refractive index is about 0.5 or less. (Ii) When judging by transmittance, the wavelength is 350 nm to 650 nm. In the visible light region, it is preferable in terms of transparency that the extinction coefficient k of each film is as low as about 0.1 or less.

  The thickness of the substrate 1 differs depending on whether or not the thin film integrated circuit device including the thin film transistor 10 is flexible, but is not particularly limited. For example, when the flexible thin film integrated circuit device used for an IC tag or the like is used. Is preferably a plastic substrate having a thickness of 5 μm to 300 μm. The shape of the substrate 1 is not particularly limited, and examples thereof include a chip shape, a card shape, and a disk shape. Note that, after the thin film integrated circuit device is formed on the single-wafer or continuous substrate 1, it may be divided into individual chips, cards, or disks.

(Gate electrode)
The gate electrode 2 is patterned on the substrate 1 as shown in FIGS. 1 to 3 and FIG. Examples of the material for forming the gate electrode include metal films such as gold, silver, copper, titanium, chromium, cobalt, nickel, aluminum, niobium, tantalum, and molybdenum; ITO (indium tin oxide), indium oxide, IZO (indium zinc) Oxide), transparent conductive films such as SnO ₂ and ZnO; Note that a transparent conductive polymer such as polyaniline, polyacetylene, a polyalkylthiophene derivative, or a polysilane derivative may be used as long as it has desired conductivity.

  For the formation of the gate electrode 2, film forming means and patterning means corresponding to the type of gate electrode material and the heat resistance of the substrate 1 are applied. For example, when forming the gate electrode 2 with a transparent conductive film, a sputtering method, various CVD methods, etc. can be applied as a film forming means, and photolithography can be applied as a patterning means. When a low temperature film formation is required for forming the gate electrode 2, a sputtering method or a plasma CVD method capable of forming a low temperature can be preferably applied as a film forming means. When the gate electrode 2 is formed of a conductive polymer, a vacuum deposition method, a pattern printing method, or the like can be applied as a film forming unit, and photolithography can be applied as a patterning unit.

  At the same time as forming the gate electrode 2, a circuit wiring group such as a gate electrode wiring, a ground wiring, and a power wiring may be formed of the same material as the gate electrode 2. The thickness of the gate electrode 2 and the thickness of the circuit wiring group (electrode or wiring) formed simultaneously with the formation of the gate electrode 2 are usually about 0.05 μm to 0.2 μm.

(Gate insulation film)
As shown in FIGS. 1 to 3, the gate insulating film 3 is provided so as to cover the gate electrode 2. Various materials can be used for the gate insulating film 3 as long as it has high insulating properties, has a relatively high dielectric constant, and is suitable as a gate insulating film. For example, silicon oxides such as silicon oxide, silicon nitride, and silicon oxynitride, nitrides, oxynitrides, and the like can be preferably exemplified. In addition, at least one or more of yttrium oxide, aluminum oxide, hafnium oxide, zirconium oxide, titanium oxide, tantalum oxide, niobium oxide, scandium oxide, and barium strontium titanate can be given. In particular, from the viewpoint of transparency, silicon oxides such as silicon oxide, silicon nitride, and silicon oxynitride, nitrides, oxynitrides, and the like are preferable.

  As shown in FIGS. 1 to 3 and FIG. 4B, the gate insulating film 3 is formed by film forming means and patterning means corresponding to the type of gate insulating film material and the heat resistance of the substrate 1. For example, when the gate insulating film 3 is formed of silicon oxide, nitride, oxynitride or the like, a sputtering method or various CVD methods can be applied as the film forming means, and photolithography can be applied as the patterning means. When the gate insulating film 3 is required to be formed at a low temperature, a sputtering method or a plasma CVD method capable of forming at a low temperature can be preferably applied as the film forming means. The thickness of the gate insulating film 3A is usually about 0.1 μm to 0.3 μm.

(Oxide semiconductor film)
In the case of the bottom gate top contact thin film transistors 10A and 10B shown in FIGS. 1, 2 and 4C, the oxide semiconductor film 4 is disposed above the gate electrode 2 with the gate insulating film 3 interposed therebetween. A pattern is formed on the gate insulating film 3. On the other hand, in the case of the thin film transistor 10C having the bottom gate bottom contact structure shown in FIG. 3, the oxide semiconductor film 4 is sourced above the gate insulating film 3 above the gate electrode 2 with the gate insulating film 3 interposed therebetween. The electrode 6S and the drain electrode 6D are patterned, and then the pattern is formed so as to straddle between the source electrode 6S and the drain electrode 6S.

  The type of the oxide semiconductor film 4 is not particularly limited as long as it has a mobility that can be used as a channel region constituting a thin film transistor. Even if it is a currently known oxide semiconductor film, It may be an oxide semiconductor film to be discovered in the future.

Examples of the oxide constituting the oxide semiconductor film 4 include an amorphous oxide containing InMZnO (M is at least one of Ga, Sn, Al, and Fe) as a main constituent element. 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.

  When the oxide semiconductor film 4 is formed of an oxide semiconductor material that is an amorphous oxide containing InMZnO, the oxide semiconductor film 4 exhibits good light transmittance particularly in the visible light region and good in the ultraviolet light region. Since it shows a light shielding property, as will be described later, it can be preferably applied as the protective film 7, and deterioration of thin film transistor characteristics can be more effectively prevented. In particular, an InGaZnO-based amorphous oxide in which M is Ga is preferable. Therefore, if the oxide semiconductor film 4 here is formed of the same amorphous oxide containing InMZnO as the protective film 7 to be described later, the manufacturing apparatus and the process can be shared, and a low-cost thin film transistor is manufactured. Convenient to.

The 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 semiconductor film used in Examples described later can be preferably exemplified. Further, the IGZO-based oxide semiconductor film may be added with Al, Fe, Sn, or the like as a constituent element, if necessary. Since the IGZO-based oxide semiconductor film transmits visible light and becomes a transparent film, it is preferably used for a thin film integrated circuit that requires transparency. In addition, since this IGZO-based oxide semiconductor film can be formed at a low temperature of about 150 ° C. from room temperature by sputtering (particularly RF sputtering), the glass transition temperature is less than 200 ° C. It can be preferably applied to a poor plastic substrate.

  Whether or not the oxide semiconductor film 4 is amorphous indicates the presence of crystalline when the oxide semiconductor 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 broad (halo shape) pattern is seen. Such a broad pattern is also observed in a microcrystalline oxide semiconductor film. Therefore, the oxide semiconductor film 4 includes such a microcrystalline oxide semiconductor film.

  For the formation of the oxide semiconductor film 4, a film forming unit and a patterning unit corresponding to the type of the oxide semiconductor material and the heat resistance of the substrate 1 are applied. For example, a sputtering method, a CVD method, or the like can be applied as a film forming unit, and photolithography can be applied as a patterning unit. However, when low temperature film formation is required, a sputtering method (particularly, RF sputtering method) The plasma CVD method can be preferably applied.

  Although the thickness of the oxide semiconductor film 4 is not generally specified because it is arbitrarily designed depending on the film formation conditions, it is usually preferably in the range of 10 nm to 150 nm, and preferably in the range of 30 nm to 100 nm. Is more preferable.

  In particular, in the present invention, it is preferable to apply an RF sputtering method (a so-called high-frequency sputtering method, including an RF magnetron sputtering method) in an oxygen gas atmosphere that does not contain argon in the oxide semiconductor film formation step. The oxide semiconductor film 4 formed in this manner has fewer oxygen vacancies in the film, and an insulating oxide semiconductor film having a low carrier concentration can be obtained. As a result, there is an advantage that the subsequent formation of the protective film 7 can be performed by the RF sputtering method and adjusted in the direction of increasing the carrier concentration.

  On the other hand, for the oxide semiconductor film formation step, an RF sputtering method may be applied in an oxygen gas atmosphere containing argon. The oxide semiconductor film 4 formed by RF sputtering under this gas condition has a large number of oxygen vacancies in the film and becomes an oxide semiconductor film having a carrier concentration suitable as an active layer. Therefore, when the oxide semiconductor film 4 is formed by applying the RF sputtering method in an oxygen gas atmosphere containing argon, the oxygen concentration is not generated at the time of sputtering and the carrier concentration is not affected when the protective film is formed thereafter. It is preferable to apply a DC sputtering method.

(Passivation film)
As shown in FIG. 2, the passivation film 5 can be provided on the oxide semiconductor film 4 in the case of a bottom gate top contact structure. Providing the passivation film 5 is effective in reducing damage to the oxide semiconductor film 4 when the source electrode 6S and the drain electrode 6D are formed directly on the oxide semiconductor film 4. Therefore, the passivation film 5 is provided to form the source electrode connection portion 4B and the drain electrode connection portion 4B while protecting the channel region 4A of the oxide semiconductor film 4. Specifically, as shown in FIG. 2, the passivation film 5 is an oxide semiconductor in a form in which contact holes are formed in the oxide semiconductor film 4 where the source electrode connection portion 4B and the drain electrode connection portion 4B are formed. The membrane 4 is covered.

The passivation film 5 can be formed by forming a passivation film material such as silica (SiO ₂ hydrate) or polyimide resin in a liquid state by a coating method, and then patterning using a resist. Alternatively, a passivation film material having photosensitivity may be formed by a coating method, followed by exposure and development to form the passivation film 5 having a predetermined pattern. The thickness of the passivation film 5 is usually about 0.1 μm to 3 μm.

  When the passivation film 5 is provided, the activation process is performed after the contact holes are formed. By this activation treatment, the conductivity of the oxide semiconductor film 4 exposed in the contact hole portion can be increased to form the source electrode connection portion 4B and the drain electrode connection portion 4B. When the source electrode 6S and the drain electrode 6D, which will be described later, are patterned on the source electrode connection portion 4B and the drain electrode connection portion 4B with enhanced conductivity, the source electrode 6S and the drain for the source electrode connection portion 4B and the drain electrode connection portion 4B, respectively. The ohmic resistance of the electrode 6D can be reduced. Note that as the activation treatment, plasma treatment is treatment means for causing oxygen vacancies in the oxide semiconductor film 4.

(Source electrode, drain electrode)
In the case of the bottom gate top contact structure shown in FIGS. 1 and 2, the source electrode 6S and the drain electrode 6D are patterned on the oxide semiconductor film 4 or on the passivation film 5 in which contact holes are formed. . On the other hand, in the case of the bottom gate bottom contact structure shown in FIG. 3, the pattern is formed on the gate insulating film 4 before the oxide semiconductor film 4 is formed.

The source electrode material and the drain electrode material are selected in consideration of ohmic contact with the source electrode connection portion 4B and the drain electrode connection portion 4B of the oxide semiconductor film 4, and for example, ITO (indium tin oxide), indium oxide, IZO Preferred examples include transparent conductive films such as (indium zinc oxide), SnO ₂ , and ZnO. Further, a conductive polymer such as polyaniline, polyacetylene, polyalkylthiophene derivative, polysilane derivative, or the like may be used as long as it has desired conductivity.

  For the formation of the source electrode 6S and the drain electrode 6D, film forming means and patterning means corresponding to the type of electrode material and the heat resistance of the substrate 1 are applied. For example, in the case of forming the source electrode 6S and the drain electrode 6D with a transparent conductive film, a sputtering method or various CVD methods can be applied as a film forming unit, and photolithography can be applied as a patterning unit. When required, a sputtering method or a plasma CVD method capable of forming a film at a low temperature can be preferably applied as a film forming means. When the source electrode 6S and the drain electrode 6D are formed using a conductive polymer, a vacuum deposition method, a pattern printing method, or the like can be applied as a film forming unit, and photolithography can be applied as a patterning unit.

  In the step of forming the source electrode 6S and the drain electrode 6D, it is preferable to simultaneously connect to an already formed circuit wiring group or form a new circuit wiring group with the same electrode material. The thickness of the source electrode 6S and the drain electrode 6D is usually about 0.1 μm to 0.3 μm.

(Protective film)
In the case of the bottom gate top contact structure shown in FIGS. 1 and 2, the protective film 7 is formed by forming the oxide semiconductor film 4 exposed between the source electrode 6S and the drain electrode 6D after forming the source electrode 6S and the drain electrode 6D. It is provided to cover at least. In the case of the bottom gate bottom contact structure shown in FIG. 3, the protective film 7 is provided so as to cover at least the oxide semiconductor film 4 exposed as the uppermost layer after patterning the oxide semiconductor film 4. Yes. Note that as long as the protective film 7 covers at least the exposed oxide semiconductor film 4, the protective film 7 may be provided so as to cover the entire surface including that portion.

  The protective film 7 thus formed is formed of an oxide semiconductor material, and is particularly preferably formed of the same oxide material as that of the oxide semiconductor film 4 already described. Since the oxide semiconductor film 4 and the protective film 7 can be formed under the same or similar film formation conditions using the same film formation chamber by being formed of the same oxide material as the oxide semiconductor film 4, Low cost can be realized. Note that since the material for forming the protective film 7 is the same as the oxide semiconductor material (specifically, amorphous oxide) that is the material for forming the oxide semiconductor film 4 described above, the details of the material are omitted here. In addition, if there is a probability that the protective film 7 is formed of the same material as the oxide semiconductor material that is the material for forming the oxide semiconductor film 4 described above, in a range that does not hinder the characteristics of the protective film, An element different from the constituent elements of the oxide semiconductor material may be included.

As in the case of the oxide semiconductor film 4, the protective film 7 is preferably made of an amorphous oxide containing InMZnO (M is at least one of Ga, Sn, Al, and Fe), and particularly InGaZnO in which M is Ga. It is preferably made of an amorphous oxide of the system. Since the protective film 7 made of an amorphous oxide containing InMZnO (particularly InGaZnO) exhibits good light transmission particularly in the visible light region and good light shielding properties in the ultraviolet light region, it has thin film transistor characteristics (ie, semiconductor characteristics). Deterioration can be prevented more effectively. Therefore, there is an effect that deterioration of the thin film transistor characteristics can be effectively prevented as compared with the conventional protective film such as SiO ₂ film and organic-inorganic composite compound film. As a result, the protective film 7 prevents deterioration of the semiconductor characteristics against ultraviolet light and improves the atmospheric stability of the semiconductor characteristics against water vapor and oxygen gas, so that the thin film transistor provided with the protective film 7 has excellent long-term reliability. It will be.

  Such a protective film 7 covers at least the oxide semiconductor film 4 exposed between the source electrode 6S and the drain electrode 6D (in the case of a bottom gate top contact structure; see FIGS. 1 and 2) or an oxide exposed as the uppermost layer. Since the oxide semiconductor film 4 is provided so as to cover at least the physical semiconductor film 4 (in the case of a bottom gate bottom contact structure; see FIG. 3), the threshold value generated when the oxide semiconductor film 4 is exposed to an ultraviolet ray or an air atmosphere. Changes and mobility changes can be suppressed.

  The protective film 7 can be formed by various methods, but is preferably formed by a sputtering method. Examples of the sputtering method include a DC sputtering method, an RF sputtering method, and a magnetron sputtering method. In this invention, it is preferable to form into a film by RF sputtering method and DC sputtering method.

  These will be described in detail.

The protective film 7 is formed by RF sputtering in a film made of an oxide semiconductor material, preferably an amorphous oxide film (referred to as an amorphous oxide film) that becomes the oxide semiconductor film 4 and does not contain argon. This is performed when a film is formed in advance by an RF sputtering method. The reason is that when an amorphous oxide film is formed by an RF sputtering method not containing argon, the amorphous oxide film has few oxygen defects and a carrier concentration of 10 ¹² ions / cm ³ to 10 ¹⁵ ions / cm ³ . An amorphous oxide film having a low carrier concentration can be obtained. When the protective film 7 is formed by RF sputtering (in an oxygen gas atmosphere not containing argon) so as to cover at least the exposed portion of the amorphous oxide film, the carrier concentration of the amorphous oxide film is set to, for example, 10 ¹⁶ ions / cm ^3. The oxide semiconductor film 4 in the semiconductor region having a carrier concentration of 10 ¹⁵ ions / cm ³ to 10 ¹⁷ ions / cm ³ can be obtained.

  Note that in the case where an amorphous oxide film to be the oxide semiconductor film 4 is formed by an RF sputtering method including argon, oxygen defects in the film increase and the carrier concentration increases, and the carrier concentration suitable as an active layer as it is. It becomes an oxide film with When the protective film 7 is formed on the exposed portion of such an amorphous oxide film by RF sputtering, the carrier concentration of the amorphous oxide film increases, and the desired oxide semiconductor film 4 cannot be obtained. .

On the other hand, the protective film 7 is formed by the DC sputtering method when an amorphous oxide film to be the oxide semiconductor film 4 is formed in advance by an RF sputtering method containing argon. The reason is that when an amorphous oxide film is formed by an RF sputtering method containing argon, the amorphous oxide film has many oxygen defects, and the carrier concentration is as high as 10 ¹⁵ ions / cm ³ to 10 ¹⁷ ions / cm ^3. A conductive amorphous oxide can be obtained. This is because even if the protective film 7 is formed by DC sputtering (under an oxygen gas atmosphere not containing argon) so as to cover at least the exposed portion of the amorphous oxide film, the carrier concentration of the semiconductor film does not change.

  The thickness of the protective film is preferably 200 nm to 300 nm, for example, and preferably 250 nm to 300 nm. If the thickness of the protective film 7 is less than 200 nm, the protective film 7 may be too thin to absorb ultraviolet rays sufficiently.

(Other membranes)
Other films may be formed on the thin film transistor 10. For example, a base film (an adhesion film or a buffer film against heat or impurity atoms) may be provided on the substrate surface to improve the adhesion of the gate electrode 2 and the adhesion and characteristic stability of the gate insulating film 3. Preferred examples of the base film include a chromium film having a thickness of 5 nm to 10 nm, a silicon oxide film, a silicon nitride film, and a silicon oxynitride film having a thickness of about 10 nm to 50 nm.

  In addition to the protective film 7 described above, another protective film (not shown) may be provided. Examples of the other protective film mentioned here preferably include a PVP (polyvinylpyrrolidone) film having a thickness of about 500 nm to 1000 nm, a gas barrier film made of silicon oxide, silicon oxynitride, or the like having a thickness of about 100 nm to 500 nm. be able to.

As described above, the thin film transistor and the manufacturing method thereof according to the present invention have an oxide semiconductor material having a good light transmission property in the visible light region and a good light shielding property in the ultraviolet light region, and the protective film is formed. Therefore, the obtained thin film transistor effectively prevents deterioration of thin film transistor characteristics (semiconductor characteristics) as compared with a thin film transistor in which a conventional protective film such as a SiO ₂ film or an organic-inorganic composite compound film is provided as a protective film. be able to. In particular, the protective film prevents deterioration of the semiconductor characteristics against ultraviolet light and improves the atmospheric stability of the semiconductor characteristics against water vapor and oxygen gas, so that the thin film transistor provided with the protective film has excellent long-term reliability. Become. Furthermore, according to the present invention, since the protective film can be formed using the same oxide material as that of the oxide semiconductor film, a thin film transistor that realizes low cost can be provided.

  In addition, in the method for manufacturing a thin film transistor according to the present invention, an oxide semiconductor film is formed by an RF sputtering method in an oxygen gas atmosphere containing no argon to form an oxide semiconductor film with few oxygen vacancies. A low insulating oxide semiconductor film can be obtained. At this time, the protective film is formed by an RF sputtering method in an oxygen gas atmosphere not containing argon, similarly to the oxide semiconductor film, so that the protective film is formed using another film formation chamber or in another gas atmosphere. It is not necessary to form a film, and the cost can be reduced. Further, at the time of RF sputtering for forming the protective film, the carrier concentration of the oxide semiconductor film can be increased to shift to semiconductor characteristics.

  In addition, according to the method for manufacturing a thin film transistor according to the present invention, the oxide semiconductor film is formed by RF sputtering in an oxygen gas atmosphere containing argon, so that the oxide semiconductor film having many oxygen vacancies is formed. Thus, an oxide semiconductor film suitable for the active layer can be obtained. At this time, since the protective film is formed by a DC sputtering method in an oxygen gas atmosphere not containing argon, an oxide suitable for an active layer without changing much the carrier concentration of the oxide semiconductor film during the DC sputtering. It can be a semiconductor film.

  The present invention will be described in more detail with representative examples. Note that the present invention is not construed as being limited to the following examples.

[Example 1]
A thin film transistor 10 shown in FIG. 1 was produced. First, a glass having a thickness of 700 μm was prepared as the substrate 1, and an aluminum film having a thickness of 150 nm was formed on the entire surface of the substrate 1 by a DC sputtering method to form a gate electrode film. The DC sputtering method at this time was formed under conditions of an output of 500 W, a pressure of 0.5 Pa, and an argon gas of 100%. Then, after forming a resist pattern by photolithography, wet etching was performed with a phosphoric acid solution, and patterning was performed so that the aluminum film became the gate electrode 2 (see FIG. 4A).

Next, silicon oxide having a thickness of 300 nm was formed on the entire surface as the gate insulating film 3 so as to cover the gate electrode 2. This gate insulating film 3 was formed using an RF magnetron sputtering apparatus on an 8-inch SiO ₂ target under conditions of an input power of 2.0 kW (= 3 W / cm ² ), a pressure of 0.3 Pa, and oxygen gas of 100% ( (See FIG. 4B).

Next, an InGaZnO amorphous oxide film (InGaZnO ₄ ) with an In: Ga: Zn ratio of 1: 1: 1 was formed to a thickness of 25 nm. For the amorphous oxide film, 4 inches of InGaZnO (In: Ga: Zn = 1: 1) under the conditions of room temperature (25 ° C.), output 500 W, pressure 0.4 Pa, and oxygen gas 100% using an RF magnetron sputtering apparatus. 1) It was formed using a target. After that, after forming a resist pattern by photolithography, wet etching was performed with a phosphoric acid solution, and the amorphous oxide film was patterned into a predetermined pattern so as to become the oxide semiconductor film 4 (see FIG. 4C). In addition, it was confirmed by “SmartLab” manufactured by Rigaku Corporation that the obtained oxide semiconductor film 4 was an amorphous phase having a broad structure having no specific crystallinity peak by X-ray diffraction measurement. .

  Next, a Ti film was formed over the oxide semiconductor film 4 by a DC sputtering method so as to have a thickness of 200 nm. The titanium film was formed using a DC sputtering apparatus under conditions of an output of 900 W, a pressure of 0.5 Pa, and an argon gas of 100%. Then, after forming a resist pattern by photolithography, wet etching was performed with a phosphoric acid solution, and patterning was performed so that the Ti film became the source electrode 6S and the drain electrode 6D. The source electrode 6S and the drain electrode 6D were formed on the gate insulating film 3 so as to have a pattern apart from a portion other than directly above the central portion of the gate electrode 2 (see FIG. 4D).

Next, the same oxide semiconductor film as the above amorphous oxide film was formed over the entire surface as a protective film. That is, an InGaZnO amorphous oxide film (InGaZnO ₄ ) with In: Ga: Zn of 1: 1: 1 was formed to a thickness of 200 nm. As in the case of the oxide semiconductor film 4, the amorphous oxide film was formed by using an RF magnetron sputtering apparatus at a room temperature (25 ° C.), an output of 500 W, a pressure of 0.4 Pa, and an oxygen gas of 100%. It was formed using an InGaZnO (In: Ga: Zn = 1: 1: 1) target (see FIG. 4E). Note that the oxide semiconductor film 4 included in the obtained thin film transistor was confirmed by X-ray diffraction measurement to exhibit a broad structure having no specific crystallinity peak.

[Example 2]
In the step of forming the oxide semiconductor film 4 of Example 1, the gas atmosphere of the amorphous oxide film was changed from an atmosphere of 100% oxygen gas to an atmosphere of Ar: O ₂ = 3: 5. went. Furthermore, in the film-forming process of the protective film 7, it carried out on the conditions changed from RF sputtering method to DC sputtering method (pressure 500W, pressure 0.4Pa, oxygen gas 100% conditions). Other than that was carried out similarly to Example 1, and produced the thin-film transistor which concerns on Example 2. FIG.

[Example 3]
In Example 1, the thin film transistor 10A having the bottom gate top contact structure was formed. In Example 4, the thin film transistor 10C having the bottom gate bottom contact structure shown in FIG. 3 was manufactured. The film forming conditions and the like were the same as in Example 1 except that the film forming order was partially different, and the thin film transistor shown in FIG. 3 was manufactured.

[Example 4]
In Example 1, the range of film forming conditions that achieve the effects of the present invention was examined by changing the film forming conditions of the oxide semiconductor film 4 in various ways. As a result, the oxide semiconductor film 4 is formed under conditions where the oxygen concentration in the deposition gas is in the range of 80% or more and the deposition pressure is 0.6 Pa or less, and the carrier concentration is 10 ¹² ions / cm ³ to 10 ¹⁵ ions. The effect of the present invention was shown within the range of / cm ³ . Film formation under conditions outside the range did not achieve the effects of the present invention.

[Comparative Example 1]
In Example 1, instead of the amorphous oxide constituting the protective film 7, the silicon oxide film has a thickness of 900 W with an RF magnetron sputtering apparatus, a film forming pressure of 0.5 Pa, and Ar: O ₂ = 3: 1. A thin film transistor according to Comparative Example 1 was fabricated in the same manner as in Example 1 except that the film was formed to a thickness of 100 nm.

[Evaluation and results]
(Evaluation of semiconductor characteristics)
In Examples 1 and 2, the carrier concentrations of the oxide semiconductor film 4 were 2.9 × 10 ¹² ions / cm ³ and 2.3 × 10 ¹² ions / cm ³ , respectively. On the other hand, in Comparative Example 1, the carrier concentration of the oxide semiconductor film 4 was 4.3 × 10 ¹³ ions / cm ³ .

(Evaluation of visible light transparency and ultraviolet light shielding properties)
The transmittance of the protective film 7 formed in Example 1 was measured by a light transmittance and reflectance spectrum measuring apparatus (FilmTek 3000, manufactured by SCI). The result is shown in FIG. From this result, the transmittance of the protective film 7 is low up to 380 nm and less than 80%, whereas in the visible light region exceeding the transmittance, the transmittance is 80% or more, and the protective film 7 is in the ultraviolet light region. It was confirmed that the light-shielding property was good and the light transmittance was good in the visible light region.

(Evaluation of light resistance)
Examples 1 and 2 and Comparative Example 1 were evaluated for light resistance. Specifically, white light of 1000 W / m ² was irradiated, and the current density at that time was measured in the range of −2 V to ² V. Compared with the thin film transistor of Comparative Example 1 in which a protective layer made of silicon oxide is provided instead of the protective film 7 made of amorphous oxide (oxide semiconductor material) according to the present invention, the value of the current density is about 1/4. Showed excellent light resistance.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Gate insulating film 4 Oxide semiconductor film 4 ′ Oxide semiconductor film exposed between source electrode and drain electrode 4A Channel region of oxide semiconductor film 4B Diffusion region of oxide semiconductor film (source electrode connection portion And drain electrode connection part)
DESCRIPTION OF SYMBOLS 5 Passivation film 5 'Passivation film exposed between source electrode and drain electrode 6 Source electrode and drain electrode 6S Source electrode 6D Drain electrode 7 Protective film 10 Thin film transistor 10A, 10B Thin film transistor (bottom gate top contact structure)
10C thin film transistor (bottom gate bottom contact structure)

Claims (2)

Forming a gate electrode pattern on the substrate; forming a gate insulating film covering the gate electrode; patterning an oxide semiconductor film on the gate insulating film; and on the oxide semiconductor film A step of forming a pattern of a source electrode and a drain electrode, and a step of forming a protective film with an oxide semiconductor material so as to cover at least the oxide semiconductor film exposed between the source electrode and the drain electrode. A manufacturing method comprising:
The oxide semiconductor film and the protective film are made of an amorphous oxide containing InMZnO (M is at least one of Ga, Sn, Al, and Fe),
The step of forming the oxide semiconductor film is a step of forming the oxide semiconductor film by RF sputtering in an oxygen gas atmosphere containing argon,
The method for producing a thin film transistor, wherein the protective film forming step is a step of forming a protective film by a DC sputtering method in an oxygen gas atmosphere not containing argon. A step of patterning a gate electrode on the substrate; a step of forming a gate insulating film covering the gate electrode; a step of patterning a source electrode and a drain electrode on the gate insulating film; and the source electrode and the drain electrode And a step of patterning an oxide semiconductor film covering at least the gate insulating film exposed therebetween, and a step of forming a protective film with an oxide semiconductor material so as to cover at least the oxide semiconductor film. A manufacturing method comprising:
The oxide semiconductor film and the protective film are made of an amorphous oxide containing InMZnO (M is at least one of Ga, Sn, Al, and Fe),
The step of forming the oxide semiconductor film is a step of forming the oxide semiconductor film by RF sputtering in an oxygen gas atmosphere containing argon,
The method for producing a thin film transistor, wherein the protective film forming step is a step of forming a protective film by a DC sputtering method in an oxygen gas atmosphere not containing argon.

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