JP2011210778A - Thin film transistor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent thin film transistor substrate where a reflection pattern such as an electrode pattern is not conspicuous.SOLUTION: The thin film transistor substrate 10 has a thin film transistor constituted of at least a gate electrode 2, a source electrode 5s and a drain electrode 5d, which are formed of transparent conductive materials, a semiconductor film 4 formed of a transparent semiconductor material and a gate insulating film 3 formed of a transparent insulating material on a transparent substrate 1. A refractive index difference (average value) in a visible light region of the respective electrodes 2, 5s and 5d, the semiconductor film 4 and the gate insulating film 3 is set to be ≤0.1. The transparent semiconductor material is an InGaZnO-based semiconductor material and the transparent conductive material is desirable to be selected from indium tin oxide, indium zinc oxide, tin oxide and zinc oxide.

Description

  The present invention relates to a thin film transistor substrate, and more particularly to a transparent thin film transistor substrate that can be applied to a display device and has an inconspicuous electrode pattern.

  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 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 semiconductor films can be formed at room temperature and can be formed without damaging 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 in spite of an amorphous material formed at a low temperature. In addition, IGZO-based oxide semiconductors are transparent materials with high transmittance to visible light, and even when a conventionally known transparent conductive material such as ITO is used as a gate electrode or a source / drain electrode, it has good electrical characteristics. Since transparent contact characteristics can be obtained, a transparent TFT using only a transparent material has been studied.

  However, when a transparent TFT is actually configured by combining transparent materials, regions having different reflectivities are generated because the refractive indexes of the respective constituent elements are different, and high interface reflection occurs depending on the location. As a result, there is a problem that even if a TFT is configured by combining transparent materials, the pattern becomes conspicuous due to reflection. This problem is a factor that lowers the visibility and deteriorates the total performance, particularly in a display device such as a liquid crystal display or an organic EL display. The cause of reflection in this case is interface reflection due to the difference in refractive index between the electrode and the refractive index of the substrate or the gate insulating layer. Patent Document 3 proposes that a layer having an intermediate refractive index is placed at the interface as an antireflection layer in order to prevent this interface reflection. That is, in Patent Document 3, for the purpose of increasing the light transmittance of the transparent TFT, (1) a transparent layer that is intermediate between the refractive indexes of both layers is placed between the substrate and the oxide semiconductor layer to further increase transparency. And (2) the refractive index of the channel layer made of an oxide semiconductor material between the substrate and the gate insulating layer is continuously increased in the film thickness direction from the refractive index of the substrate to the refractive index of the gate insulating layer. An example has been proposed in which the transparency is increased by changing the shape in steps.

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

JP 2004-103957 A JP 2005-88726 A JP 2007-73703 A JP 2001-160486 A

  However, in the invention described in FIG. 1 and FIG. 2 of Patent Document 3, sufficient transmittance is ensured in the portion where the channel layer and the gate insulating layer are laminated, but for example, in the portion where the electrode is formed. Thus, reflection at the interface occurs at portions where the layer configuration is different. In that case, a reflective pattern corresponding to the electrode pattern is observed. With regard to transparency, when the transmittance is simply increased to improve the light utilization efficiency, the reflection pattern based on the interface reflection is not particularly problematic. However, in a display device such as a liquid crystal display or an organic EL display, the reflection pattern of the electrode pattern described above becomes a problem.

  In addition, it is difficult to manufacture and it is not practical to selectively provide a transparent layer having a specific refractive index described in Patent Document 3 or a channel layer having an inclined refractive index on all interfaces having different refractive indexes. .

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a transparent thin film transistor substrate that can be applied to a display device and in which a reflection pattern such as an electrode pattern is not conspicuous.

  A thin film transistor substrate according to the present invention for solving the above-described problems comprises a gate electrode, a source electrode and a drain electrode made of a transparent conductive material, a semiconductor film made of a transparent semiconductor material, and a transparent insulating material on a transparent base material. A thin film transistor substrate having a thin film transistor composed of at least a gate insulating film, wherein a refractive index difference (average value) in a visible light region of each electrode, the semiconductor film, and the gate insulating film is 0.1 or less It is characterized by being.

  According to this invention, the refractive index difference (average value) in the visible light region between each electrode and the gate insulating film and the refractive index difference (average value) in the visible light region between the semiconductor film and the gate insulating film are any. Is less than 0.1, interface reflection is unlikely to occur. Therefore, for example, when applied as a drive element of a display device, it is possible to provide a transparent thin film transistor substrate in which the reflection at the reflection pattern is difficult to visually recognize by minimizing the interfacial reflection between the layers in each of the portions having different layer configurations. As a result, it is possible to realize a smooth and high-quality display in which the reflective pattern is not visually recognized.

  In the thin film transistor substrate according to the present invention, the transparent semiconductor material is an InGaZnO-based semiconductor material.

  According to the present invention, an oxide semiconductor film to which an InGaZnO-based semiconductor material is applied is excellent in transparency, and is provided under the inverted stagger type TFT in which the oxide semiconductor film is provided on the gate insulating film and the gate insulating film. In any of the provided staggered TFTs, it functions sufficiently as a circuit element having necessary and sufficient mobility, and can be applied in various fields as a driving element for a display device such as a liquid crystal display or an organic EL display. In addition, since there is no problem in contact characteristics with an electrode made of an oxide-based transparent conductive material, it is advantageous in constructing a transparent TFT as a whole. Further, since the refractive index is about 2.0, which is almost the same as the refractive index of the oxide-based transparent conductive material, there is an advantage that reflection at the interface with the electrode does not occur. Further, since the refractive index difference with the gate insulating film is 0.1 or less, reflection at the interface with the gate insulating film does not occur.

  In the thin film transistor substrate according to the present invention, the transparent conductive material is selected from indium tin oxide, indium zinc oxide, tin oxide, and zinc oxide.

  According to the present invention, each electrode (gate electrode, source electrode and drain electrode) to which each of the above transparent conductive materials is applied is excellent in transparency and has a refractive index of about 2.0. No reflection occurs at the interface with the gate insulating film which is 0.1 or less. In addition, there is no problem in contact characteristics with an oxide semiconductor film to which the above InGaZnO-based semiconductor material is applied, and there is an advantage that reflection at the interface with the electrode does not occur because the refractive index is almost the same.

  In the thin film transistor substrate according to the present invention, the gate insulating film has a refractive index in the range of 1.85 to 2.05.

  The refractive index of the transparent conductive material is usually around 2.0, and the refractive index of the transparent semiconductor material is usually around 2.0. By applying a gate insulating film having a refractive index in the above range, for example, display When applied as a driving element of an apparatus, a transparent thin film transistor substrate can be obtained in which reflection at a reflection pattern is difficult to visually recognize by minimizing interfacial reflection between layers in different parts of a layer structure.

  As described above, the present invention controls the refractive index of each material constituting the thin film transistor substrate so that the reflection at each part in the plane having a different layer structure is made the same level. The visibility is lowered and a high-quality display is realized. Specifically, (1) both are oxide-based materials, and an oxide semiconductor material such as an InGaZnO-based material having an index of refraction of approximately 2.0 and an oxide-based transparent conductive material are applied. (2) By applying a material having a refractive index difference similar to that of the oxide semiconductor and each electrode (within 0.1) to the gate insulating film instead of the conventionally used silicon oxide For example, when applied as a driving element of a display device, the distribution of interfacial reflection between layers in different parts of the layer structure is made as small as possible, making it difficult to see the reflection pattern seen in conventional electrode patterns, etc. It is. In addition, as long as it has such a structure, the thin film transistor which constitutes the thin film transistor substrate according to the present invention may be an inverted staggered type or a forward staggered type.

  According to the thin film transistor substrate according to the present invention, interface reflection is unlikely to occur. Therefore, when applied as a driving element of a display device, for example, a reflection pattern is formed by minimizing interface reflection between layers in different parts of a layer structure. As a result, it is possible to realize a smooth and high-quality display in which the reflective pattern is not visually recognized.

It is typical sectional drawing which shows an example (inverted stagger type | mold) of the thin-film transistor substrate which concerns on this invention. It is a top view of the thin-film transistor substrate shown in FIG. It is typical sectional drawing which shows another example (order stagger type | mold) of the thin-film transistor substrate which concerns on this invention. It is typical sectional drawing which shows another example (inverted stagger type | mold) of the thin-film transistor substrate which concerns on this invention. It is typical sectional drawing which shows the example (reverse stagger type | mold) of the conventional thin-film transistor substrate. FIG. 6 is a plan view of the thin film transistor substrate shown in FIG. 5.

  Hereinafter, a thin film transistor substrate 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.

[Basic configuration]
The thin film transistor substrate 10 (10A, 10B, 10C) according to the present invention includes a gate electrode 2, a source electrode 5s and a drain electrode 5d made of a transparent conductive material on a transparent substrate 1, as shown in FIGS. And a thin film transistor (hereinafter referred to as “TFT”) composed of at least a semiconductor film 4 made of a transparent semiconductor material and a gate insulating film 3 made of a transparent insulating material. The TFT constituting the TFT substrate 10 may be an inverted stagger type (see FIGS. 1, 2 and 4) or a forward stagger type (see FIG. 3).

  In the present invention, the refractive index difference (average value) in the visible light region between each electrode (the gate electrode 2, the source electrode 5s, and the drain electrode 5d; the same applies hereinafter) and the gate insulating film 3 is 0.1 or less. And the difference in refractive index (average value) in the visible light region between the semiconductor film 4 and the gate insulating film 3 is 0.1 or less. By comprising in this way, the interface reflection between layers can be made as small as possible in each part in a plane where layer composition differs. As a result, when the thin film transistor substrate 10 is applied as a drive element of a display device that requires transparency, it is possible to realize a smooth and high-quality display in which a reflective pattern is not visually recognized.

  Here, “in-plane” means In-plane (in-plane: a direction parallel to the surface of the transparent substrate 1), which is a two-dimensional direction of the transparent substrate surface, and is the X direction shown in FIG. Or the Y direction (only the X direction is displayed in FIG. 1). The “visible light region” refers to a wavelength of 400 to 700 nm, and the refractive index (average value) is compared at a wavelength of 633 nm. The refractive index difference was evaluated by the average value of the number of measurements n = 3. Note that the requirement that each component (each electrode, gate insulating film, semiconductor film, etc.) is expressed as “transparent” is that the transmittance of each component is an element of reflection at the interface in the visible light region of wavelength 400 to 700 nm. Except for, it is about 80% or more.

(Example)
Next, the form of the TFT substrates 10A to 10C shown in FIGS. 1, 3, and 4 will be described.

  A TFT substrate 10A shown in FIG. 1 includes an inverted staggered TFT provided on a transparent substrate 1, and includes a transparent substrate 1 and a gate electrode 2 formed on the transparent substrate 1 in a predetermined pattern. A gate insulating film 3 formed so as to cover the gate electrode 2, a semiconductor film 4 formed in a predetermined pattern on the gate insulating film 3 and immediately above the gate electrode 2, and a center on the semiconductor film 4 It has at least a source electrode 5s and a drain electrode 5d that are spaced apart and patterned.

  A TFT substrate 10B shown in FIG. 3 is a substrate in which a forward stagger type TFT is provided on a transparent substrate 1, and a predetermined region (a portion that becomes a channel region) on the transparent substrate 1 and the transparent substrate 2. The source electrode 5s and the drain electrode 5d, which are spaced apart and patterned, are formed in a predetermined pattern so as to fill a predetermined region between the source electrode 5s and the drain electrode 5d and straddle the electrodes 5s and 5d. The semiconductor film 4, the gate insulating film 3 formed on the semiconductor film 4, the source electrode 5s and the drain electrode 5d so as to cover them, and the gate electrode 2 formed on the gate insulating film 3 in a predetermined pattern And at least.

  A TFT substrate 10C shown in FIG. 4 is obtained by providing on a transparent substrate 1 a material obtained by further adding a passivation film 6 to the inverted staggered TFT shown in FIG. A gate electrode 2 formed in a predetermined pattern on 1, a gate insulating film 3 formed so as to cover the gate electrode 2, and formed in a predetermined pattern on the gate insulating film 3 and immediately above the gate electrode 2 The semiconductor film 4, the passivation film 6 having contact holes 8 and 8 in the electrode connection portions 7 and 7 of the semiconductor film 4, and the source electrode 5 s and the drain electrode connection portion 7 connected to the source electrode connection portion 7 are connected. It is comprised at least by the drain electrode 5d.

(Difference in refractive index between layers)
FIG. 1 shows an inverted stagger type TFT substrate 10A. In FIG. 1, IN <b> 1 is an interface between the transparent substrate 1 and the gate electrode 2, IN <b> 2 is an interface between the gate electrode 2 and the gate insulating film 3, and IN <b> 3 is the transparent substrate 1 and the gate insulating film 3. IN4 is an interface between the gate insulating film 3 and the semiconductor film 4, IN5 is an interface between the gate insulating film 3 and the source / drain electrodes 5s and 5d, and IN6 is an interface between the semiconductor film 4 and the source / drain electrodes. An interface between the drain electrodes 5s and 5d, IN7 is an interface between the semiconductor film 4 and air, IN8 is an interface between the source / drain electrodes 5s and 5d and air, and IN9 is an interface between the gate insulating film 3 and air. Is the interface. In the inverted staggered TFT substrate 10A according to the present invention, the refractive index difference (average value) in the visible light region between each electrode (the gate electrode 2, the source electrode 5s, and the drain electrode 5d) and the gate insulating film 3 is 0.1. And the difference in refractive index (average value) in the visible light region between the semiconductor film 4 and the gate insulating film 3 is 0.1 or less. The interface reflection of .about.IN6 can be minimized.

  Note that the difference in refractive index between the IN1 interface between the transparent substrate 1 and the gate electrode 2 and the IN3 interface between the transparent substrate 1 and the gate insulating film 3 exceeds 0.1, and further, IN7 between the semiconductor film 4 and air. The interface and the IN8 interface between the source / drain electrodes 5s, 5d and the air have a refractive index difference of more than 0.1, but each of these interfaces is uniformly overlapped in the in-plane direction of the TFT substrate 10A. It is provided on the entire surface. As a result, the gate line 11 (provided with the same material as the gate electrode 2) and the data line 12 (provided with the same material as the source / drain electrodes 5s and 5d) and the pixel electrode 13 (source) shown in FIG. Even when the drain electrodes 5s and 5d are provided with the same material.), A conspicuous reflection pattern does not occur.

  FIG. 3 shows a forward stagger type TFT substrate 10B. 3, IN11 is an interface between the transparent substrate 1 and the source / drain electrodes 5s and 5d, IN12 is an interface between the transparent substrate 1 and the semiconductor film 4, and IN13 is an interface between the transparent substrate 1 and the transparent substrate 1. An interface between the gate insulating film 3, IN 14 is an interface between the source / drain electrodes 5 s and 5 d and the semiconductor film 4, and IN 15 is an interface between the source / drain electrodes 5 s and 5 d and the gate insulating film 3, IN16 is an interface between the semiconductor film 4 and the gate insulating film 3, IN17 is an interface between the gate insulating film 3 and the gate electrode 2, IN18 is an interface between the gate electrode 2 and air, and IN19 is a gate insulating film. 3 is an interface between air and air. Similarly to the above, the forward stagger type TFT substrate 10B according to the present invention has a difference in refractive index (average value) in the visible light region between each of the electrodes (gate electrode 2, source electrode 5s and drain electrode 5d) and the gate insulating film 3 as 0. .1 and the refractive index difference (average value) in the visible light region between the semiconductor film 4 and the gate insulating film 3 is 0.1 or less. The interface reflection of .about.IN17 can be minimized.

  The interface between IN11 to IN14 has a refractive index difference exceeding 0.1, and the interface between IN18 and IN19 also has a refractive index difference exceeding 0.1. These interfaces are in the in-plane direction of the TFT substrate 10B. They are uniformly provided on the entire surface without overlapping. As a result, a conspicuous reflection pattern does not occur.

  FIG. 4 shows an inverted staggered TFT substrate 10 </ b> C having a passivation film 6. 4 are the same as those in FIG. IN21 is an interface between the gate insulating film 3 and the passivation film 6, IN22 is an interface between the semiconductor film 4 and the passivation film 6, and IN23 is an interface between the semiconductor film 4 and the source / drain electrodes 5s and 5d. IN24 is an interface between the passivation film 6 and the source / drain electrodes 5s and 5d, and IN25 is an interface between the passivation film 6 and air. Similarly to the above, the inverted staggered TFT substrate 10C according to the present invention has a refractive index difference (average value) in the visible light region between each electrode (the gate electrode 2, the source electrode 5s, and the drain electrode 5d) and the gate insulating film 3 is 0. .1 and the refractive index difference (average value) in the visible light region between the semiconductor film 4 and the gate insulating film 3 is 0.1 or less. , IN4, IN23 can reduce the interface reflection as much as possible.

  In addition, although the refractive index difference of each interface between IN1 and IN3 exceeds 0.1, these interfaces are uniformly provided on the entire surface without overlapping in the in-plane direction of the TFT substrate 10C. A conspicuous reflection pattern does not occur. Further, IN21, IN22, and IN24 that are interfaces with the passivation film 6 also have a refractive index difference of 0.1, and interface reflection can be minimized. Although the refractive index difference between IN25 and IN8 greatly exceeds 0.1 at the interface with air, high visibility is ensured without recognizing the pattern because the interface with the same refractive index difference is formed over the entire surface. it can. In order to ensure high visibility in such a state, it is sufficient that the refractive index of the passivation film 6 is the same as the refractive index of the gate insulating film 3 (refractive index difference is 0.1 or less).

On the other hand, the configuration of the conventional TFT substrate 100 shown in FIG. 5 is the same as that of the TFT substrate 10A shown in FIG. 1, but the gate insulating film 103 is a SiO ₂ film having a refractive index of 1.45. The refractive index difference (average value) in the visible light region between each of the electrodes (the gate electrode 102, the source electrode 105s, and the drain electrode 105d) and the gate insulating film 103 exceeds 0.1, and the semiconductor film The refractive index difference (average value) in the visible light region between the gate 104 and the gate insulating film 103 also exceeds 0.1. As a result, the refractive index difference between IN1 and IN3 is different in each part in the plane having different layer configurations, and is not uniform in the in-plane direction. Further, interface reflection occurs at IN1 and IN2 which are the upper and lower interfaces of the gate electrode 102. As a result, a pattern-like reflection pattern becomes conspicuous due to reflection generated at the interface where the gate electrode 102 contacts the transparent substrate 1 and the interface where the gate electrode 102 contacts the gate insulating film 103.

  Thus, in the present invention, the refractive index of each element constituting the TFT is about 2.0, and the refractive index difference between each of the electrodes 2, 5 s, 5 d and the semiconductor film 4 and the gate insulating film 3 is 0. .1 or less. For this reason, the interfaces (IN1, IN3) between the constituent elements of the TFT and the transparent base material 1 are the interfaces having the main refractive index difference. In the present invention, the refractive index difference at the interface is the entire surface of the TFT substrate 10. And uniform. As a result, reflection at the interface occurs to the same extent on the entire surface of the TFT substrate 10, so that no reflection pattern is generated as a whole.

  When the TFT substrate 10 of the present invention is applied to a liquid crystal display or an organic EL display, the refractive index of the liquid crystal layer or the organic EL layer is about 1.5. The reflection generated at the interface between the TFT substrate 10 of the present invention and the liquid crystal layer or the organic EL layer is not noticeable due to the display of the liquid crystal layer or the organic EL layer, but the present invention does not cause a problem. It is possible to prevent problems caused by reflection of a circuit portion or a wiring portion of a TFT not provided with an organic EL layer.

[Each component]
Hereinafter, components of the TFT substrate 10 according to the present invention will be sequentially described.

(Transparent substrate)
The transparent substrate 1 is for mounting a TFT thereon and forming a TFT substrate 10 according to the present invention. The kind and structure of the transparent base material 1 are not specifically limited, A flexible material, a hard material, etc. are selected according to a use. Specific examples of materials that can be used include glass, quartz, polyethylene, polypropylene, polyethylene terephthalate, polymethacrylate, polymethyl methacrylate, polymethyl acrylate, polyester, and polycarbonate. Usually, a glass substrate with ITO or a plastic substrate with ITO, which is a transparent conductive material, is preferably used.

  Although the refractive index of a glass base material changes with kinds of glass, it is 1.45-1.85 normally. Moreover, although the refractive index of a plastic base material also changes with kinds of plastic, it is 1.40-1.70 normally. These refractive indexes are represented by an average value of values measured at a wavelength of 633 nm using ellipsometry. Particularly in the present invention, in the case of a glass substrate, the average value of the refractive index at a wavelength of 633 nm is preferably 1.46 to 1.58, and in the case of a plastic substrate, the refractive index at a wavelength of 633 nm is preferred. Those having an average value of 1.40 to 1.65 are preferred. More specifically, the glass substrate is preferably an aluminosilicate glass having a refractive index of 1.50 to 1.51 at a wavelength of 633 nm, and the plastic substrate has a refractive index of 1.60 at a wavelength of 633 nm. PET of ˜1.63 is preferred. A glass substrate or plastic substrate having such a refractive index can be selected from commercially available products.

  The thickness of the transparent substrate 1 varies depending on whether or not the obtained TFT substrate 10 is flexible, and is not particularly limited. For example, the flexible TFT substrate 10 used in a liquid crystal display device or an organic EL device is used. In this case, a plastic substrate having a thickness of 5 to 300 μm is preferably used. On the other hand, when flexibility is not required, a glass substrate or plastic substrate having a thickness of 100 to 3000 μm is preferably used. Further, the shape of the transparent substrate 1 is not particularly limited, and examples thereof include a panel shape, a chip shape, a card shape, and a disk shape. In addition, after forming TFT on the sheet-like or continuous transparent base material 1, you may divide and process into individual panel shape, chip shape, card shape, and disk shape.

(Gate electrode)
The gate electrode 2 is provided in a predetermined pattern on the transparent substrate 1 in the inverted staggered TFT of FIGS. 1 and 4, and in the forward staggered TFT of FIG. 3 are provided in a predetermined pattern. In the present invention, the gate electrode 2 is a transparent electrode made of a transparent conductive material. As the transparent conductive material, for example, an oxide transparent conductive material such as ITO (indium tin oxide), indium oxide, IZO (indium zinc oxide), SnO ₂ , or ZnO is used. Note that a transparent conductive polymer such as polyaniline, polyacetylene, a polyalkylthiophene derivative, or a polysilane derivative may be used as long as it is transparent and has a desired conductivity.

The refractive index of the gate electrode 2 is usually 1.90 to 2.0, although it varies depending on the type of transparent conductive material. As described above, the refractive index is expressed as an average value of values measured at a wavelength of 633 nm using ellipsometry. Particularly, in the present invention, those having an average refractive index of 1.93 to 1.98 at a wavelength of 633 nm are preferable. More specifically, ITO having a refractive index of 1.95 to 1.96 at a wavelength of 633 nm, ZnO having a refractive index of 1.96 to 1.97 at a wavelength of 633 nm, and a refractive index of 1.93 at a wavelength of 633 nm. ˜1.95 SnO ₂ is particularly preferred. Such a range of the refractive index can be adjusted by film forming conditions when the gate electrode 2 is formed (for example, oxygen partial pressure in a gas atmosphere during sputtering film formation).

  The gate electrode 2 is formed by film forming means and patterning means corresponding to the type of transparent conductive material that is the gate electrode material and the heat resistance of the transparent substrate 1. In the present invention, since the gate electrode 2 is formed of an oxide transparent conductive material, a sputtering method, various CVD methods, or the like is applied as a film forming unit, and photolithography is applied as a patterning unit. In addition, when low temperature film-forming is requested | required by applying the non-heat-resistant transparent base material 1, such as a plastic substrate, the sputtering method and plasma CVD method in which low-temperature film formation is possible are applied as a film-forming means. When the gate electrode 2 is formed from a conductive polymer, a vacuum deposition method, a pattern printing method, or the like is applied as a film forming unit, and photolithography is applied as a patterning unit.

  At the time of forming the gate electrode 2, as shown in FIG. 2, the pattern formation of the gate line 21 and the wiring from the gate line 21 to the gate electrode 2 can be simultaneously formed with the same material as the gate electrode 2. . The thickness of the gate electrode 2 and the thickness of the wiring formed simultaneously when the gate electrode 2 is formed are set in consideration of the allowable wiring width and the resistance value of the transparent conductive material to be applied. The thickness is usually about 0.1 to 0.3 μm.

(Gate insulation film)
Various materials can be used for the gate insulating film 3 as long as it is transparent, has high insulating properties, has a relatively high dielectric constant, and is suitable as a gate insulating film. In the present invention, the gate insulating film 3 can be used. It is necessary to match the refractive index (average value) of each electrode (the gate electrode 2, the source electrode 5 s and the drain electrode 5 d) with the refractive index of the semiconductor film 4. Specifically, the difference (refractive index difference) between the refractive index (average value) of the gate insulating film 3 and the refractive index (average value) of each electrode becomes 0.1 or less, and the refractive index of the gate insulating film 3 ( The gate insulating film 3 is formed so that the difference (refractive index difference) between the average value) and the refractive index (average value) of the semiconductor film 4 is 0.1 or less.

  In the present invention, it is preferable to form the gate insulating film 3 on the entire surface. Specifically, in the reverse stagger type TFT of FIG. 1 and FIG. 4, it is formed on the entire surface so as to cover the gate electrode 2 on the transparent base material 1, and in the forward stagger type TFT of FIG. Preferably, it is formed on the entire surface so as to cover the upper source / drain electrodes 5s, 5d and the semiconductor film 4. In the present invention, since the gate insulating film 3 having a small refractive index difference (0.1 or less) with the electrodes 2, 5s, 5d and the semiconductor film 4 is formed, the refractive index difference of each element constituting the TFT can be reduced. As a result, reflection at the laminated interface of elements can be significantly reduced.

  In the case where the gate insulating film 3 is provided only in a predetermined region without being provided on the entire surface of the TFT substrate 10, it is desirable to cover the entire surface with a transparent protective layer to be described later. In this case, it is desirable that the refractive index of the transparent protective layer is substantially the same as that of the gate insulating film 3 (difference in refractive index between the electrodes 2, 5s and 5d and the semiconductor film 4 is 0.1 or less).

As a material for forming the gate insulating film 3, an oxide insulating film such as ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , or CeO ₂ can be preferably used. The gate insulating film 3 made of these materials has a refractive index of about 2.0 at a wavelength of 633 nm, and specifically has a refractive index of 1.85 to 2.05 at a wavelength of 633 nm. . The gate insulating film 3 having such a refractive index range can have a refractive index difference of 0.1 or less with respect to the gate electrode 2, the semiconductor film 4, and the source / drain electrodes 5s and 5d, which have a refractive index of about 2.0. . Specifically, the refractive index of ZrO _{2 at} a wavelength of 633 nm is 2.02 to 2.05, the refractive index of HfO _{2 at} a wavelength of 633 nm is 1.92 to 1.95, and Ta ₂ O ₅ The refractive index at a wavelength of 633 nm is 2.00 to 2.05, and the refractive index of CeO _{2 at} a wavelength of 633 nm is 2.00 to 2.05. The refractive index of each oxide is convenient because the refractive index can be in the above range under normal film formation conditions. Further, the film formation conditions such as the oxygen partial pressure in the gas atmosphere and the material composition during sputtering film formation The refractive index can be finely adjusted to a desired value by adjusting.

Note that SiO ₂ used as a general gate insulating film has a refractive index of about 1.45 at a wavelength of 633 nm. Therefore, the refractive index difference between each electrode and the semiconductor film 4 having a refractive index of around 2.0 is larger than 0.1 (about 0.5), reflection at the interface is likely to occur, and the reflection pattern becomes conspicuous. .

  The gate insulating film 3 is formed by a film forming means and a patterning means corresponding to the type of gate insulating film material and the heat resistance of the transparent substrate 1. In the case of forming the oxide-based gate insulating film 3 described above, a sputtering method or various CVD methods can be applied as a film forming unit, and photolithography can be applied as a patterning unit. For the film forming means, a sputtering method or a plasma CVD method capable of forming a film at a low temperature can be preferably applied. The thickness of the gate insulating film 3 is usually about 0.1 to 0.3 μm.

(Semiconductor film)
As the semiconductor film 4, an oxide-based semiconductor film which is a film formed of a transparent semiconductor material and has a mobility that can be used as a channel region constituting a TFT is used. By making the semiconductor film 4 oxide-based, all the constituent elements of the TFT according to the present invention are oxide-based, and the adhesion of each layer is good. Furthermore, an oxide-based film has an advantage that its characteristics can be finely adjusted by film forming conditions. The type of the oxide semiconductor film 4 is not particularly limited, and may be a currently known oxide semiconductor film or an oxide semiconductor film to be discovered in the future.

  In the inverted staggered TFT shown in FIGS. 1 and 4, the semiconductor film 4 is provided on the gate insulating film 3 in a predetermined pattern in which the upper portion of the gate electrode 2 becomes a channel region. On the other hand, the forward stagger type TFT shown in FIG. 3 is provided in a predetermined pattern so as to fill a predetermined region between the source electrode 5s and the drain electrode 5d and straddle both the electrodes 5s and 5d.

  The semiconductor film 4 has a refractive index difference of 0.1 or less with respect to the gate insulating film 3. By using the semiconductor film 4 having such a refractive index difference as a constituent element of the TFT, the refractive index difference as a whole TFT is reduced, and the reflection pattern can be made as small as possible by preventing interface reflection.

Examples of the transparent semiconductor material forming the semiconductor film 4 include amorphous oxides containing InMZnO (M is at least one of Ga, 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.

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”) semiconductor material used in Examples described later can be preferably used. Further, the IGZO-based semiconductor material may be added with Al, Fe, Sn, or the like as a constituent element, if necessary. Since the semiconductor film 4 made of this IGZO-based semiconductor material can be formed at a low temperature of about 150 ° C. from room temperature, it can be applied to a plastic substrate having a glass transition temperature of less than 200 ° C. and poor heat resistance. It can be preferably applied.

  The semiconductor film 4 made of each semiconductor material described above has a refractive index of about 2.0 at a wavelength of 633 nm, and specifically, a refractive index at a wavelength of 633 nm is in the range of 1.92 to 2.00. is there. In the semiconductor film 4 having such a refractive index range, the refractive index difference with respect to the gate electrode 2, the gate insulating film 3, and the source / drain electrodes 5 s and 5 d having a refractive index of about 2.0 can be made 0.1 or less. . Specifically, the refractive index at a wavelength of 633 nm of an IGZO-based semiconductor material that is particularly preferably used is 1.94 to 1.97. The refractive index of the semiconductor film 4 formed of each semiconductor material is convenient because it can be set to a refractive index in the above range under normal film formation conditions. Furthermore, the oxygen partial pressure and the composition of the gas atmosphere during sputtering film formation are convenient. The refractive index can be finely adjusted to a desired value by adjusting film forming conditions such as film temperature.

  Whether the semiconductor film 4 is amorphous or not is a clear diffraction peak indicating the presence of crystalline when X-ray diffraction is performed at a low incident angle of about 0.5 ° on the semiconductor film to be measured. Is not detected, that is, a so-called halo pattern is observed. Since the halo pattern is also observed in the microcrystalline oxide semiconductor film, the semiconductor film 4 includes such a microcrystalline oxide semiconductor film.

  For the formation of the semiconductor film 4, film forming means and patterning means corresponding to the type of 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 the film forming unit, and photolithography can be applied as the patterning unit. Note that when low-temperature film formation is required, sputtering or plasma CVD can be preferably applied as film formation means. The thickness of the semiconductor film 4 is not generally specified because it is arbitrarily designed depending on the film formation conditions, but is usually preferably in the range of 10 to 150 nm, more preferably in the range of 30 to 100 nm. preferable. If necessary, the semiconductor film 4 may be subjected to heat treatment after film formation to improve semiconductor characteristics (mobility) or stabilize specific resistance. Examples of the heat treatment include laser irradiation and thermal annealing.

(Source electrode, drain electrode)
In the inverted staggered TFT shown in FIG. 1, the source electrode 5s and the drain electrode 5d are formed in a pattern spaced apart from the central portion of the semiconductor film 4, and in the forward staggered TFT shown in FIG. In an inverted stagger type TFT in which a predetermined region (a portion that becomes a channel region) is opened and spaced apart on the material 2 to form a pattern, and the passivation film 6 shown in FIG. 4 is provided, the electrode connection portion 7 of the semiconductor film 4 is formed. , 7 are formed on the passivation film 6 having contact holes 8, 8 so as to be connected to the electrode connection portions 7, 7.

The source electrode material and the drain electrode material are preferably transparent conductive materials capable of matching the energy level with the oxide semiconductor film 4 described above. For example, as in the case of the gate electrode 2, transparent conductive materials such as ITO (indium tin oxide), indium oxide, IZO (indium zinc oxide), SnO ₂ and ZnO can be preferably exemplified. Further, a conductive polymer such as polyaniline, polyacetylene, polyalkylthiophene derivative, and polysilane derivative may be used as long as it has desired transparency and conductivity. In particular, since the semiconductor film 4 is an oxide semiconductor film, it is preferable to form the source electrode 5s and the drain electrode 5d with a transparent conductive material of the same oxide.

The refractive indexes of the source electrode 5s and the drain electrode 5d are usually 1.90 to 2.00, although they differ depending on the type of the transparent conductive material. As in the case of the gate electrode 2 described above, the refractive index is an average value of values measured at a wavelength of 633 nm using ellipsometry. Particularly, in the present invention, those having an average refractive index of 1.93 to 1.98 at a wavelength of 633 nm are preferable. More specifically, ITO having a refractive index of 1.95 to 1.96 at a wavelength of 633 nm, ZnO having a refractive index of 1.96 to 1.97 at a wavelength of 633 nm, and a refractive index of 1.93 at a wavelength of 633 nm. ˜1.95 SnO ₂ is particularly preferred. Such a range of refractive index can be adjusted by film forming conditions at the time of forming the source / drain electrodes (for example, oxygen partial pressure in a gas atmosphere at the time of sputtering film formation).

  For the formation of the source electrode 5s and the drain electrode 5d, a film forming unit and a patterning unit corresponding to the type of the electrode material and the heat resistance of the transparent substrate 1 are applied. For example, when the source electrode 5s and the drain electrode 5d are formed of a transparent conductive material, 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 5s and the drain electrode 5d are 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.

  In the process of forming the source electrode 5s and the drain electrode 5d, for example, a power supply wiring line and a ground wiring line for the drain electrode can be patterned simultaneously, and a data electrode line, a scan wiring line, and a power supply wiring line can be patterned simultaneously. The thickness of the source electrode 5s and the drain electrode 5d, and the thickness of the electrodes and wirings formed simultaneously when forming the source electrode 5s and the drain electrode 5d are usually about 0.1 to 0.3 μm.

(Passivation film)
The passivation film 6 can be provided as needed as shown in FIG. The passivation film 6 is connected to the source electrode 5s while protecting the channel region of the semiconductor film 4 when the source electrode 5s and the drain electrode 5d connected to the semiconductor film 4 are formed after the semiconductor film 4 is formed. Provided to form a connection portion 7 between the portion 7 and the drain electrode 5d. Specifically, as shown in FIG. 4, the passivation film 6 has a configuration in which a contact hole 8 is formed in a portion of the semiconductor film 4 where the connection portion 7 to the source electrode 5s and the connection portion 7 to the drain electrode 5d are formed. The semiconductor film 4 is covered with

  For the passivation film 6, it is preferable to use the same type of material as the gate insulating film 3 (that is, a material having a similar refractive index) for the purpose of reducing the difference in refractive index at the interface. A passivation film 5 having a predetermined pattern may be formed by a photolithography process after film formation by sputtering or the like. The thickness of the passivation film 5 is usually about 0.1 to 3 μm.

The refractive index of the passivation film 6 formed of the above material varies depending on the type of the material. For example, the refractive index at a wavelength of 633 nm of the passivation film 6 made of a ZrO ₂ film is usually 2.02 to 2.05. . These refractive indexes have a refractive index difference of 0.1 or less with respect to each of the above constituent elements (gate electrode 2, gate insulating film 3, semiconductor film 4, source / drain electrodes 5s, 5d) constituting the TFT of the present invention. Become.

  In addition, after providing the passivation film 6 having the contact hole 8, an activation process is performed. By this activation treatment, the conductivity of the semiconductor film 4 exposed in the contact hole 8 can be increased to form the connection portion 7 with the source electrode 5s and the connection portion 7 with the drain electrode 5d. When the source electrode 5s and the drain electrode 5d are formed in a pattern on the connection portion 7 with the source electrode and the drain electrode 5d having enhanced conductivity, the connection portion 7 with the source electrode and the drain electrode 5d The ohmic resistance of the source electrode 5s and the drain electrode 5d with respect to each of the connection portions 7 can be reduced. As the activation process, the plasma process is a processing unit that causes oxygen vacancies in the semiconductor film 4.

(Other membranes)
Even if it is a component other than the above, the TFT substrate 10 according to the present invention may include other transparent films as long as it is within the scope of the present invention.

  For example, in the example of FIG. 1, a transparent adhesion film or a buffer film (not shown) may be provided on the transparent substrate surface to enhance the adhesion of the gate electrode 2 and the adhesion of the gate insulating film 3. Moreover, after forming the source electrode 5s and the drain electrode 5d, you may provide the transparent protective film (not shown) which covers the whole. Preferred examples of the transparent adhesive film or buffer film include a silicon oxide film, a silicon nitride film, and a silicon oxynitride film having a thickness of about 10 to 50 nm. In addition, as a transparent protective film, an organic protective film such as a PVP (polyvinylpyrrolidone) film having a thickness of about 500 to 1000 nm, a gas barrier inorganic protection made of silicon oxide or silicon oxynitride having a thickness of about 100 to 500 nm, etc. A membrane can be preferably mentioned.

  Although the refractive index of the above-mentioned adhesion film or protective film varies depending on the type of the material, for example, the refractive index at a wavelength of 633 nm of the silicon oxide film is usually 1.45 to 1.48. For example, the refractive index of the PVP film at a wavelength of 633 nm is usually 1.50 to 1.55. These refractive indexes are separated from the above-described constituent elements (gate electrode 2, gate insulating film 3, semiconductor film 4, source / drain electrodes 5s, 5d) constituting the TFT of the present invention, and the difference in refractive index is 0. Over 1 The purpose of the present invention is to prevent partial interfacial reflection so that the reflection pattern does not stand out as a whole. Therefore, these films are not provided in a predetermined pattern, but are provided on the entire surface. By doing so, the interface reflection occurring between other components can be made uniform over the entire surface of the TFT substrate 10, and the reflection pattern can be made inconspicuous.

  Moreover, you may provide various wiring as needed. The wiring is arbitrarily designed depending on the circuit design. For example, a power supply wiring line, a ground wiring line, a data electrode line, a scan wiring line, and the like may be provided.

  As described above, according to the present invention, the refractive index of each material constituting the TFT substrate 10 is controlled so that the reflection at each part in the plane having a different layer structure is made to be the same. It is possible to realize a high-quality display. Specifically, (1) both are oxide-based materials, and an oxide semiconductor material such as an InGaZnO-based material having an index of refraction of approximately 2.0 and an oxide-based transparent conductive material are applied. (2) The gate insulating film 3 is made of a material having a refractive index difference similar to that of the oxide semiconductor and each electrode (within 0.1) instead of the conventionally used silicon oxide. Therefore, for example, when applied as a driving element of a display device, the distribution of interfacial reflection between layers in each part in a plane having a different layer structure is made as small as possible to make it difficult to visually recognize a reflection pattern seen in a conventional electrode pattern or the like. be able to. As long as having such a configuration, the TFT constituting the TFT substrate according to the present invention may be an inverted stagger type as shown in FIGS. 1 and 4, or a forward stagger type as shown in FIG. Also good.

  In the present invention, since all the components of the TFT are made of oxide, there is an advantage that the adhesion of each layer is good. Furthermore, an oxide-based film has an advantage that its characteristics can be finely adjusted by film forming conditions.

  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 TFT substrate 10A shown in FIG. 1 was produced. First, an ITO (indium tin oxide) film having a thickness of 100 nm was formed on a glass substrate 1 having a thickness of 0.7 mm by a sputtering method, and then patterned by photolithography to form a gate electrode 2 having a wiring width of 30 μm. The refractive index (average value) of the glass substrate was 1.50 at a wavelength of 633 nm, and the refractive index (average value) of the gate electrode 2 was 1.97 at a wavelength of 633 nm.

Next, a ZrO ₂ film having a thickness of 200 nm was formed as a gate insulating film 3 over the entire surface of the glass substrate including the gate electrode 2 so as to cover the gate electrode 2 by a sputtering method. The refractive index (average value) of this ZrO ₂ film was 2.03 at a wavelength of 633 nm.

  Next, an InGaZnO-based oxide semiconductor film 4 having a thickness of 100 nm is formed on the gate insulating film 3 by a sputtering method (composition example: using a target of In: Ga: Zn = 1: 1: 1). Then, patterning was performed by photolithography. The patterning was performed by wet etching using an acidic mixed solution containing oxalic acid. The refractive index (average value) of the semiconductor film 4 was 1.96 at a wavelength of 633 nm.

  Finally, IZO having a thickness of 200 nm was formed by sputtering and then patterned by photolithography to form a source electrode 5s and a drain electrode 5d. The refractive index (average value) of the source / drain electrodes 5s and 5d was 1.97 at a wavelength of 633 nm. Thus, a TFT substrate 10A according to Example 1 was manufactured.

The ZnO ₂ film, the ITO film, and the IZO film described below were patterned by dry etching using CF ₄ gas as an etching gas. This patterning can also be performed by wet etching using buffered hydrofluoric acid (buffered hydrofluoric acid). The refractive index of each film constituting the TFT substrate 10A was measured by an optical film thickness measurement system (Filmtek manufactured by SCI).

[Example 2]
A TFT substrate 10B shown in FIG. 3 was produced. First, an ITO (indium tin oxide) film having a thickness of 100 nm is formed on a glass substrate 1 having a thickness of 0.7 mm by a sputtering method, and then patterned by photolithography to form a predetermined region (a portion that becomes a channel region). Separated source electrode 5s and drain electrode 5d were formed. The refractive index (average value) of the glass substrate was 1.50 at a wavelength of 633 nm, and the refractive index (average value) of the source electrode 5s and the drain electrode 5d was 1.97 at a wavelength of 633 nm.

  Next, an InGaZnO-based oxide semiconductor film 4 having a thickness of 100 nm is formed by a sputtering method so as to cover the source electrode 5s and the drain electrode 5d (a composition example: In: Ga: Zn = 1: 1: 1 is used). And then patterned by photolithography. The patterning was performed by wet etching using an acidic mixed solution containing oxalic acid. The refractive index (average value) of the semiconductor film 4 was 1.96 at a wavelength of 633 nm.

Next, a ZrO ₂ film having a thickness of 200 nm was formed as a gate insulating film 3 on the entire surface covering the semiconductor film 4, the source electrode 5s, and the drain electrode 5d by a sputtering method. The refractive index (average value) of this ZrO ₂ film was 2.03 at a wavelength of 633 nm.

  Finally, IZO having a thickness of 200 nm was formed by sputtering and then patterned by photolithography to form the gate electrode 2. The refractive index (average value) of the gate electrode 2 was 1.97 at a wavelength of 633 nm. Thus, a TFT substrate 10B according to Example 2 was produced.

[Example 3]
A TFT substrate 10C shown in FIG. 4 was produced. In Example 1, the passivation film 6 was formed after forming the semiconductor film 4 and before forming the source electrode 5s and the drain electrode 5d. Specifically, after the semiconductor film 4 is formed, an insulating film having a thickness of 100 nm is formed by sputtering a ZrO ₂ film on the entire surface covering the semiconductor film 4, and then patterned to passivate the semiconductor film 4. A film 6 was formed. In this patterning, a contact hole 8 for connecting the source electrode 5 s and the drain electrode 5 d is formed in the semiconductor film 4, and the connection portion 7 with the source electrode 5 s and the connection portion 7 with the drain electrode 5 d are formed on the semiconductor film 4. Done to form. Subsequently, plasma treatment was performed. By the plasma treatment, the openings of the contact holes 8 and 8 where the passivation film 6 is not provided are made conductive. In this plasma treatment, oxygen vacancies can be generated in the oxide semiconductor film by performing plasma irradiation in a CF ₄ or CHF ₃ fluorine-based gas (also Ar gas) atmosphere. To conductor properties. By this plasma treatment, the semiconductor film 4 exposed at the site where the contact holes 8 and 8 are formed becomes a conductor, and the connection with the source electrode 5s and the drain electrode 5d formed thereafter can be made favorable. Further, the channel region covered with the passivation film 6 is protected by the passivation film 6 and does not impair the semiconductor characteristics.

  After this plasma treatment, as in Example 1, IZO having a thickness of 200 nm was formed by a sputtering method and then patterned by photolithography to form a source electrode 5s and a drain electrode 5d. In this way, a TFT substrate 10C according to Example 3 was manufactured.

[Example 4]
In Example 1, as a gate electrode, a ZnO film having a thickness of 100 nm was used instead of ITO. Other than that was carried out similarly to Example 1, and produced the TFT substrate which concerns on Example 4. FIG. The refractive index at 633 nm of the ZnO film was 1.94.

[Example 5]
In Example 1, a gate insulating film in which 200 nm of HfO ₂ was formed instead of ZrO ₂ was used. Other than that was carried out similarly to Example 1, and produced the TFT substrate which concerns on Example 5. FIG. The refractive index at 633 nm of the HfO ₂ film was 1.93.

[Example 6]
In Example 1, as the gate insulating film, the film formation conditions of the ZrO ₂ film were changed, and the film was formed under the film formation condition of 1.0 Pa instead of the sputter film formation with a pressure of 0.3 Pa. A TFT substrate according to Example 6 was made in the same manner as Example 1 except for the above. The refractive index at 633 nm of the ZrO ₂ film was 1.85.

[Example 7]
In Example 1, as the gate insulating film, the film formation conditions of the ZrO ₂ film were changed, and instead of performing the sputter film formation at a pressure of 0.3 Pa, the film was formed under the film formation condition of 0.2 Pa. A TFT substrate according to Example 7 was made in the same manner as Example 1 except for the above. The refractive index at 633 nm of the ZrO ₂ film was 2.05 because the film forming pressure was 0.2 Pa.

  As described above, in each example, the gate insulating film 3 having a refractive index of approximately 2.0 (1.85 to 2.05) and the refractive index having a refractive index difference with respect to the gate insulating film 3 of 0.1 or less. Other films (gate electrode 2, semiconductor film 4, source / drain electrodes 5s, 5d) are in direct contact. And the interface whose refractive index difference exceeds 0.1 is only the interface with the transparent substrate 1. As a result, the TFT substrate has uniform interface reflection as a whole, and the pattern-like reflection pattern does not stand out.

[Comparative Example 1]
A TFT substrate having the form shown in FIGS. 5 and 6 was produced in the same manner as in Example 1 except that the gate insulating film 3 was changed to a 200 nm thick SiO ₂ film in Example 1. The refractive index (average value) of the SiO ₂ film was 1.45 at a wavelength of 633 nm. The SiO ₂ film was formed by a sputtering method and then patterned by photolithography. The patterning of the SiO ₂ film was performed by dry etching using CF ₄ gas as an etching gas.

  Although the TFT substrate thus obtained was transparent as a whole, it produced about 20% light reflection in the part where the gate electrode was present, and about 10% reflection in the other part. There was a reflection pattern that was not possible.

[Comparative Example 2]
A TFT substrate of Comparative Example 2 shown in FIG. 5 was produced in the same manner as in Example 1 except that the gate insulating film 3 was changed to a SiN _x film having a thickness of 300 nm. The refractive index (average value) of the SiN _x film was 1.94 at a wavelength of 633 nm. The SiN _x film was formed by sputtering. However, in order to set the refractive index to 1.94, the SiN _x film was formed at a film forming pressure: 0.3 Pa, power: 450 W, and Ar / N ₂ = 50 sccm / 50 sccm. Then, patterning was performed by photolithography. The patterning of the SiN _x film was also performed by dry etching using CF ₄ gas as an etching gas.

The TFT substrate thus obtained was transparent as a whole and the reflection pattern was not conspicuous. However, when the SiN _x film was formed under film forming conditions with a refractive index of 1.94, the rise voltage of the TFT characteristics was low. In the first place, it could not be used as a TFT.

[Comparative Example 3]
A TFT substrate of Comparative Example 3 shown in FIGS. 5 and 6 was fabricated in the same manner as in Example 1, except that the gate insulating film 3 was changed to a SiN _x film having a thickness of 300 nm. The refractive index (average value) of the SiN _x film was 1.79 at a wavelength of 633 nm. The SiN _x film was formed by a sputtering method, but was formed at a film forming pressure of 1.0 Pa, a power of 450 W, and Ar / N ₂ = 50 sccm / 50 sccm in order to set the refractive index to 1.79. Then, patterning was performed by photolithography. The patterning of the SiN _x film was also performed by dry etching using CF ₄ gas as an etching gas.

The TFT substrate thus obtained was transparent as a whole, but the refractive index of the SiN _x film was 1.79, and the refractive index difference with the gate insulating film 3 exceeded 0.1. Therefore, reflection occurs at the interface between the gate electrode 2 and the source / drain electrodes 5s and 5d that are in direct contact with the SiN _x film, and the reflection pattern becomes conspicuous.

[Comparative Example 4]
A TFT substrate of Comparative Example 4 shown in FIGS. 5 and 6 was fabricated in the same manner as in Example 1 except that the gate insulating film 3 was changed to a 300 nm thick SiON film in Example 1. The refractive index (average value) of the obtained SiON film was 1.67 at a wavelength of 633 nm. The SiON film was formed by sputtering, but in order to set the refractive index to 1.67, the film formation pressure: 0.6 Pa, the power: 900 W, Ar / O ₂ / N ₂ = 20 sccm / ₂ sccm / 50 sccm Then, the film was formed by photolithography and then patterned by photolithography. The patterning of the SiON film was also performed by dry etching using CF ₄ gas as an etching gas.

  The TFT substrate thus obtained was transparent as a whole, but the refractive index of the SiON film was 1.67, and the refractive index difference with the gate insulating film 3 exceeded 0.1. Therefore, reflection occurs at the interface between the gate electrode 2 and the source / drain electrodes 5s and 5d which are in direct contact with the SiON film, and the reflection pattern becomes conspicuous. As a result of a follow-up experiment in which the film formation conditions were changed, it was difficult to make the SiON film have a refractive index of about 2.0 even if the film formation conditions were changed.

DESCRIPTION OF SYMBOLS 1 Transparent base material 2 Gate electrode 3 Gate insulating film 4 Semiconductor film 5s Source electrode 5d Drain electrode 6 Passivation film 7 Connection part 8 Contact hole 10 (10A, 10B, 10C) Thin-film transistor substrate 11 Gate line 12 Data line 13 Pixel electrode

IN1 Interface between transparent substrate and gate electrode IN2 Interface between gate electrode and gate insulating film IN3 Interface between transparent substrate and gate insulating film IN4 Interface between gate insulating film and semiconductor film IN5 Gate insulating film and source / drain electrode IN6 Interface between semiconductor film and source / drain electrode IN7 Interface between semiconductor film and air IN8 Interface between source / drain electrode and air IN9 Interface between gate insulating film and air IN11 Transparent substrate and source / drain electrode IN12 Interface between transparent substrate and semiconductor film IN13 Interface between transparent substrate and gate insulating film IN14 Interface between source / drain electrode and semiconductor film IN15 Interface between source / drain electrode and gate insulating film IN16 Semiconductor film IN17 Interface between gate insulating film and IN17 Interface between gate insulating film and gate electrode IN18 Gate power IN19 Interface between gate insulating film and air IN21 Interface between gate insulating film and passivation film IN22 Interface between semiconductor film and passivation film IN23 Interface between semiconductor film and source / drain electrode IN24 Passivation film and source film Interface with drain electrode IN25 Interface between passivation film and air

DESCRIPTION OF SYMBOLS 100 Thin-film transistor substrate 101 Transparent base material 102 Gate electrode 103 Gate insulating film 104 Semiconductor film 105s Source electrode 105d Drain electrode 106 Pixel electrode 107 Gate line 108 Data line

Claims (4)

A thin film transistor substrate having a thin film transistor comprising at least a gate electrode, a source electrode and a drain electrode made of a transparent conductive material, a semiconductor film made of a transparent semiconductor material, and a gate insulating film made of a transparent insulating material on a transparent base material There,
A thin film transistor substrate, wherein a refractive index difference (average value) in the visible light region of each of the electrodes, the semiconductor film, and the gate insulating film is 0.1 or less.   The thin film transistor substrate according to claim 1, wherein the transparent semiconductor material is an InGaZnO-based semiconductor material.   The thin film transistor substrate according to claim 1, wherein the transparent conductive material is selected from indium tin oxide, indium zinc oxide, tin oxide, and zinc oxide.   4. The thin film transistor substrate according to claim 1, wherein a refractive index of the gate insulating film is in a range of 1.85 to 2.05.

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