JPH0675143B2 - Active matrix substrate - Google Patents

Description

The present invention relates to an active matrix having switching elements such as thin film transistors (hereinafter referred to as “TFT”) for forming a matrix display device in combination with liquid crystal or the like. Regarding the substrate.

(Prior Art) An example of a conventional active matrix substrate used in a matrix type liquid crystal display device is shown in FIG.

This example active matrix substrate is an inverted stagger type.
The TFT1 is used as an address switching element, and the gate electrode (gate bus line) 3, on the insulating substrate 2,
Gate insulating film 4, a-Si semiconductor film 13, insulating film 5, ohmic contact n ⁺ -a-Si contact film 6, source electrode (source bus line) 7, drain electrode 8, display pixel electrode 9, and The protective film 10 is laminated and configured. A matrix liquid crystal display device is formed by enclosing the liquid crystal between this substrate and the other substrate that faces it.

An additional capacitance electrode 11 is formed on the insulating substrate 2 below the display pixel electrode 9.

The additional capacitance electrode 11 is provided to form an additional capacitance in parallel with the capacitance of the liquid crystal arranged on the display pixel electrode 9, and therefore the additional capacitance electrode 11 and the pixel electrode are provided. A gate insulating film 4 is interposed as a dielectric layer between the gate insulating film 4 and the gate insulating film 9.

This additional capacitance is provided to improve the pixel potential holding characteristic and to reduce the level shift of the pixel electrode potential due to the overlapping capacitance between the gate electrode and the drain electrode when the gate voltage rises.

(Problem to be Solved by the Invention) In such a structure of the conventional active matrix substrate, since the transparent conductive film is used as the additional capacitance electrode 11, the resistance of the additional capacitance electrode 11 is relatively high, and the drive circuit There was a problem that the load on the server increased.

To reduce the resistance of the additional capacitance electrode 11, the film thickness of the electrode may be increased or the electrode width may be increased. However, if the film thickness is increased, the step difference at the edge portion of the electrode for the additional capacitance becomes large, and the source electrode or the like of the TFT1 formed in a later step is easily broken.

On the other hand, when the width of the additional capacitance electrode 11 is increased, there is a high possibility that the additional capacitance electrode 11 is short-circuited with the pixel electrode 9 and the source electrode 8. In addition, the capacitance between the additional capacitance electrode 11 and the source electrode 8 increases, which causes a signal level shift.

In order to solve the above-mentioned problem, it is conceivable to adopt a structure as shown in FIG. In this configuration, TFT1
The gate electrode 3 and the additional capacitance electrode 11 are formed of tantalum (hereinafter abbreviated as “Ta”). Further, as an insulating film of the additional capacitance electrode 11, a tantalum oxide film (hereinafter abbreviated as “Ta ₂ O ₅ film”) formed by anodizing the surface of the additional capacitance electrode 11 and a silicon nitride film (hereinafter Abbreviated as “SiNx film”) and has a two-layer structure. That is, by using the electrode film made of Ta, the electric resistance of the electrode for the additional capacitance is lowered, thereby reducing the load on the driver.

However, as the display area of the liquid crystal display device increases, it is required to further reduce the electrode resistance of the additional capacitance electrode 11. Therefore, even when Ta is used as the material of the additional capacitance electrode 11, it is required to further reduce the electrode resistance.

On the other hand, it is known that the electric resistance of Ta can be lowered by adding a small amount of nitrogen when forming the Ta film. Therefore,
It is considered that the additional capacitance electrode 11 may be formed of a Ta film containing a small amount of nitrogen. However, it contained nitrogen
When a Ta ₂ O ₅ film is formed by anodizing the Ta film, the Ta ₂ O ₅ film has a dielectric constant of Ta ₂ O ₅ thin film formed by anodizing the Ta film that does not contain nitrogen. Lower than
There is a problem that the added capacity becomes small. That is, when the electrode for additional capacitance is formed by using the Ta film containing nitrogen, it is possible to lower the electrode resistance, but there is a problem that the additional capacitance becomes small.

Therefore, an object of the present invention is to provide an active matrix substrate having a structure capable of reducing the electrode resistance of an electrode for additional capacitance without reducing the additional capacitance and having excellent productivity.

(Means for Solving the Problems) In an active matrix substrate of the present invention, a plurality of picture element electrodes are arranged in a matrix on an insulating substrate, switching elements are connected to the picture element electrodes, and An active matrix substrate provided with a tantalum additional capacitance electrode below, wherein the additional capacitance electrode has a two-layer structure, and nitrogen is added as an impurity to a lower layer of the two-layer structure. The upper layer is nitrogen-free, and a tantalum oxide film is formed on at least the surface of the upper layer, whereby the above object is achieved.

(Examples) The present invention will be described below with reference to Examples.

FIG. 1 is a sectional view of one embodiment of the present invention. In this embodiment, the gate electrode 3 and the additional capacitance electrode 11 are both the first
It has a two-layer structure of a Ta layer and a second Ta layer. First
The Ta layers 3a and 11a are Ta layers containing nitrogen, and the second Ta layers 3b and 11b are Ta layers containing no nitrogen. Therefore, the first Ta layers 3a and 11a formed below
Has a lower electric resistance than the second Ta layers 3b and 11b formed above.

Further, an insulating film 12 made of Ta ₂ O ₅ having a thickness of about 2000 Å, which is obtained by anodizing the surface of the second Ta layer 11b, is formed on the additional capacitance electrode 11. In this embodiment, the Ta ₂ O ₅ insulating film 12 is formed by anodizing the surface of the second Ta layer 11b containing no nitrogen. Therefore, the dielectric constant of the Ta ₂ O ₅ insulating film is higher than that in the case of forming the Ta ₂ O ₅ insulating film on the Ta film containing nitrogen as in the conventional example.

That is, in the present embodiment, since the electric resistance of the first Ta layer 11a is low, the electric resistance of the additional capacitance electrode 11 is lowered, and furthermore, the surface of the second Ta layer 11b is anodized. Thus, a Ta ₂ O ₅ insulating film 12 having a high dielectric constant is formed.

The dielectric layer constituting the additional capacitance is also composed of the Ta ₂ O ₅ insulating film 12 and the extended gate insulating film 4 in this embodiment as well.
Although it has a layered structure, the dielectric layer only needs to have at least the Ta ₂ O ₅ insulating film 12, and it is not always necessary to stack the gate insulating film 4, or a part other than the gate insulating film 4 Other dielectric layers may be further laminated in addition to the gate insulating film 4.

The gate electrode 3 also has a two-layer structure like the additional capacitance electrode 11, but the gate electrode 3 does not necessarily have to have the same two-layer structure as the additional capacitance electrode 11. However, it is preferable in terms of manufacturing process that the gate electrode 3 and the additional capacitance electrode 11 are manufactured in the same process. Therefore, it is preferable that the gate electrode 3 also has the same two-layer structure as the additional capacitance electrode 11 as in the above embodiment.

Hereinafter, the manufacturing method of this example will be described more specifically to clarify the details of this example.

On an insulating substrate 2 made of a glass substrate, Ta doped with nitrogen is sputtered to form a thin film of 2000 Å (first
It is formed on the Ta layer 11a). Furthermore, T not doped with nitrogen
A is laminated by sputtering to a thickness of 1000 Å, and this is patterned by photoetching to form the gate electrode 3 of the TFT 1 and the additional capacitance electrode 11 on the same plane and arranged at a constant pitch. Next, the surface of the second Ta layer 11b of the additional capacitance electrode 11 is oxidized by an anodic oxidation method to obtain about 2
A Ta ₂ O ₅ insulating film 12 having a thickness of 000Å is formed.

After that, the insulating film 4 made of SiNx is formed by the plasma CVD method.
A 000Å thickness is deposited on the front surface to form a dielectric layer for gate insulation film and additional capacitance. Semiconductor film 13 continuously made of a-Si
Is formed to a thickness of 300 Å and used as the semiconductor film of TFT1. Further, the insulating film 5 made of SiNx is formed on the semiconductor film 13 to a thickness of 2000 Å. By patterning this by photoetching, the patterned semiconductor film 13 and the patterned insulating film 5 are formed in the vicinity of just above the gate electrode 3. That is, the semiconductor film 13 and the insulating film 5 are arranged in a matrix corresponding to the TFTs arranged in a matrix.

Next, an n ⁺ -a-Si film is formed to a thickness of 400 Å by the plasma CVD method and pattern-processed by photoetching to form the patterned semiconductor contact film 6 in contact with the source electrode and the drain electrode. Form.

Next, a source electrode 7 and a drain electrode 8 having a pattern suitable for a TFT are formed by forming Ti, Mo, W or the like to a thickness of 3000 Å by a sputtering method or an electron beam evaporation method and pattern-processing by photo-etching.
To form. Through the above steps, the switching TFT 1 is manufactured.

Next, a transparent conductive film containing indium oxide as a main component is formed to a thickness of 1000 Å by a sputtering method or an electron beam evaporation method, and this is patterned by photoetching to connect the drain electrode 8 of the TFT and one end thereof. A rectangular display pixel electrode 9 having the other end extended to just above the additional capacitance electrode 11 is formed. Further, a protective film 10 made of SiNx is deposited on this by a plasma CVD method to a thickness of 5000 Å. As described above, it is possible to obtain an active matrix substrate provided with a gate electrode and an additional capacitance electrode having a two-layer structure of Ta thin films having different crystal structures. A liquid crystal display device can be obtained by bonding this active matrix substrate and another substrate having a counter electrode and enclosing a liquid crystal between both substrates.

The nitrogen doping amount is appropriately determined according to the desired additional capacity, the ratio of low resistance, and the like.

(Effects of the Invention) As described above, in the present invention, the electric resistance of the additional capacitance electrode can be reduced without reducing the additional capacitance. Therefore,
INDUSTRIAL APPLICABILITY The active matrix substrate of the present invention is suitable as a substrate for a large-sized liquid crystal display device in which reduction of the electrode resistance of the additional capacitance electrode is strongly required, and it is possible to effectively improve the image quality.

[Brief description of drawings]

1 is a sectional view of an embodiment of the present invention, FIG. 2 (a) is a plan view showing an example of a conventional active matrix substrate, and FIG. 2 (b) is BB of FIG. 2 (a). FIG. 3 is a sectional view taken along the line, and FIG. 3 is a sectional view for explaining an improved example of the active matrix substrate. 1 ... TFT, 2 ... insulating substrate, 3 ... gate electrode, 4
...... Gate insulating film, 7 …… Source electrode, 8 …… Drain electrode, 9 …… Pixel electrode, 11 …… Additional capacitance electrode, 11a…
... first Ta layer, 11b ... second Ta layer, 12 ... Ta ₂ O ₅ insulating film.

Claims (1)

[Claims] 1. A plurality of picture element electrodes are arranged in a matrix on an insulating substrate, a switching element is connected to the picture element electrodes, and a tantalum additional capacitance electrode is provided below the picture element electrodes. In the active matrix substrate, the additional capacitance electrode has a two-layer structure, nitrogen is added as an impurity to a lower layer of the two-layer structure, and the upper layer is a nitrogen-free one. And an active matrix substrate having a tantalum oxide film formed on at least the surface of the upper layer.