JP3265622B2 - Manufacturing method of liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an active matrix type liquid crystal display device and its with reduced manufacturing steps of the storage capacitor
And a method for producing the same.

A liquid crystal display device includes a simple matrix type and an active matrix type, which are selectively used depending on the application. The active matrix type includes a thin film transistor in each pixel, and the transistor is used when a specific pixel is selected. Is turned on, otherwise O
Since the FF is set, crosstalk can be suppressed even when the number of scanning lines is large, and a high contrast ratio can be obtained.

[0003] Therefore, it is suitable for large-area display, and its practical use is being promoted.

[0004]

2. Description of the Related Art FIG. 4 shows an equivalent circuit of an active matrix type liquid crystal display device, and FIG. 5 is a front view showing the arrangement of thin film transistors (TFTs), pixels and auxiliary capacitors.

More specifically, a plurality of gate buses 1 and a plurality of drain buses 2 are orthogonal to each other, and a thin film transistor (TFT) 3 is provided at the intersection thereof. A capacity 5 and an auxiliary capacity 6 are connected in parallel to a source electrode 4 of the TFT 3. Take a structure to arrange.

That is, the source electrode 4 of the TFT is connected to the pixel 7
However, since the pixel 7 is configured by using the transparent electrode 8 as an electrode and interposing a liquid crystal between the transparent electrode 8 and a transparent electrode formed on another glass substrate, It has a capacitance and can be electrically shown as a capacitance 5.

However, there is a problem that the capacitance is insufficient only with the capacitance 5, and that the switching operation of the TFT 3 causes flicker (flicker) and afterimage (burn-in) of the screen.

Therefore, it is necessary to add an auxiliary capacitor 5.
A storage capacitor electrode 9 is formed on a glass substrate, and an auxiliary film 6 is formed by opposing an insulating film formed on the glass substrate to the dielectric and the transparent electrode 8.

FIG. 3 is a cross-sectional view showing a conventional structure of an inverted staggered TFT, a pixel and an auxiliary capacitor, which is manufactured by the following steps. That is, a metal such as aluminum (Al) or tantalum (Ta) is formed to a thickness of about 100 nm on a glass substrate 11 made of borosilicate glass or the like and having a thickness of about 1 mm. The gate electrode 12 and the auxiliary capacitance electrode 13 are formed by performing selective etching using photolithography.

Next, a gate insulating film 14 is formed by coating an insulator such as silicon nitride (Si ₃ N _x ) to a thickness of about 400 nm by a plasma CVD method. Next, an amorphous silicon film (hereinafter referred to as an a-Si film) serving as the operation layer 15 and a Si ₃ N _x film are formed thereon by a plasma CVD method or the like, and a Si ₃ N
_{The x} film is patterned using a photolithography technique to form a channel protection film 16.

Next, an amorphous silicon film (n ⁺ a-Si film) 17 to which an n-type impurity is added and a Ti film 18 and an Al film for assisting adhesion are formed by a plasma CVD method. The drain electrode 19 is connected to a drain bus line (not shown) by performing patterning using a photolithography technique.
Then, a source electrode 20 is formed.

Next, after a protective film 21 is formed thereon by a plasma CVD method, the protective film 21 in the pixel formation portion is etched to open a window, and tin oxide (SnO ₂ ) and indium oxide (In ₂ oxide) are formed.
After a transparent conductive film made of a solid solution of O ₃ ) (abbreviated as ITO) is formed by a sputtering method or the like, patterning is performed using a photolithography technique, and the transparent electrode 8 is patterned to complete a pixel and an auxiliary capacitor. ing.

Although a TFT is made in this way,
The auxiliary capacitance is formed on the glass substrate 11 at the same time as the gate electrode 12 by using the auxiliary capacitance electrode 13 as one electrode.
14 and the protective film 21 are made of a dielectric material, and the transparent electrode 8 is used as a counter electrode.

Here, as described above, it is desirable that the auxiliary capacitance is large in order to eliminate flickering and afterimages on the screen, but since the auxiliary capacitance electrode is formed below the pixel, Preferably, the electrodes are rather reduced.

[0015]

In an active matrix type liquid crystal display device using a TFT, an auxiliary capacitor is provided below a pixel in order to eliminate flickering and an afterimage of a screen during a switching operation of the TFT. Electrically, it is desirable that the capacitance is larger than before, while
From the aspect of image display, it is necessary to reduce the size of the auxiliary capacitance electrode to improve the effective display area (aperture ratio).

[0016]

SUMMARY OF THE INVENTION The above problem is a thin film transistor and the pixel electrode and the auxiliary capacitance on a substrate Te manufacturing method smell <br/> of the liquid crystal display device obtained by forming a matrix shape, on a substrate, A gate electrode of the thin film transistor;
Simultaneously pattern the auxiliary capacitance electrode of the auxiliary capacitance
Process and the pattern of the gate electrode and the auxiliary capacitance electrode.
Forming a gate insulating film on the substrate, comprising:
Operating layer and source electrode / drain electrode of transistor
Forming a protective film covering the thin film transistor.
Forming and removing the protective film in the pixel electrode formation region
Exposing the source electrode and the gate insulating film
In contact with the exposed source electrode and the gate insulating film.
Forming a pixel electrode, and using the gate insulating film as a dielectric.
Manufacturing a liquid crystal display device including a step of forming an auxiliary capacitor
Method, or in place of the dielectric film in place of the gate insulating film,
Liquid crystal using oxide film obtained by electrolytic oxidation of auxiliary capacitor electrode surface
This can be solved by a method for manufacturing a display device .

[0017]

As described above, in the active matrix type liquid crystal display, it is necessary to add an auxiliary capacitance for improving the image quality, and the required capacitance is determined by the gate capacitance and the pixel capacitance of the TFT.

For example, the gate length is 10 μm and the gate width is 20 μm.
When the size of the pixel electrode is set to 255.times.90 .mu.m using an m.sup.m TFT, a storage capacitor electrode having a pattern of about 50.times.90 .mu.m is used under the pixel.

Here, the conventional dielectric of the auxiliary capacitance has a two-layer structure of the gate insulating film 14 and the protective film 21 as shown in FIG. 3, and is made of Si ₃ N _x having a thickness of about 700 nm. Is formed.
Therefore, the inventor intends to make the auxiliary capacitor smaller and larger by reducing the thickness of the dielectric, and employs any of the following methods. The dielectric of the storage capacitor is formed only of the gate insulating film. An auxiliary capacitance electrode is formed of Al, and an aluminum oxide film obtained by electrolytically oxidizing Al is used as a dielectric.

The present invention has been made in view of the fact that the driving of the TFT is performed at a low voltage, and thus the auxiliary capacitance does not necessarily require a high breakdown voltage, thereby reducing the size of the auxiliary capacitance electrode. be able to.

[0021]

【Example】

 Embodiment 1 (Related to Claim 1, Corresponding to FIG. 1) FIG. 1 is a sectional view showing an embodiment of the present invention.

That is, after Al is formed to a thickness of 100 nm on a glass substrate 11 by a sputtering method, a photolithography technique is used to form a gate electrode 12 having a gate length of 10 μm and a gate width of 20 μm.
m, and the auxiliary capacitance electrode 13 has a width of 25 μm and a length of 90 μm.
A pattern was formed to a size of μm.

Next, as a gate insulating film 14 on the substrate including these patterns, Si ₃ N _x is formed to a thickness of 350 nm by a high-temperature plasma CVD method keeping the substrate temperature at 350 ° C. An active layer 15 composed of an a-Si film, a channel protective film 16, an n ⁺ a-Si film 17, a Ti film 18, and an Al film are sequentially formed on the gate insulating film 14 using a photolithography technique. Perform dry etching, drain electrode 19, source electrode 20, and
A bus line (not shown) is patterned.

Next, Si ₃ N _x was placed on the substrate at a substrate temperature of 200 ° C.
The protective film 21 is formed to have a thickness of 350 nm by a low-temperature plasma CVD method for keeping the thickness of the protective film 21, which is not different from the conventional process.

That is, in the pixel forming portion, an auxiliary capacitance electrode 13 is provided on a glass substrate 11, on which a gate insulating film 14 made of Si ₃ N _x and a protective film 21 are laminated. Next, after coating the resist on the entire region on the substrate, only the pixel electrode formation region was opened, and plasma etching was performed under the following conditions to remove only the protective film 21 which was formed at a low temperature and was easily etched. .

Etchant: CF ₄ and O ₂ (composition ratio 1: 0.1) Total flow rate: 500 sccm Gas pressure: 20 Pa Microwave power: 800 W Next, ITO was formed to a thickness of 100 nm by sputtering, and photographed. The transparent electrode 8 was formed using an etching technique.

That is, the thickness of the conventional auxiliary capacitor is 700 nm.
Therefore, an area of 50 × 90 μm was necessary for the auxiliary capacitance electrode 13, but the area was reduced to 25% by halving the film thickness.
It is possible to reduce the size to 90 μm, thereby improving the aperture ratio.

The gate insulating film may be formed of a composite film, for example, Si ₃ N ₄ / SiO ₂ instead of a single film as in this example. In this case, the protective film 21 is excluded. It is effective to remove the upper layer of the gate insulating film at the same time. Embodiment 2 (Related to Claim 2, Corresponding to FIG. 2) FIG. 2 is a sectional view showing an embodiment of the present invention.

That is, after Al is formed to a thickness of 500 nm on a glass substrate 11 by a sputtering method, a photolithography technique is used to form a gate electrode 12 having a gate length of 10 μm and a gate width of 20 μm.
m, and the auxiliary capacitance electrode 13 has a width of 5 μm and a length of 90 μm.
A pattern was formed to a size of μm.

Next, as a gate insulating film 14 on the substrate including these patterns, Si ₃ N _x is formed to a thickness of 350 nm by a high-temperature plasma CVD method keeping the substrate temperature at 350 ° C. An active layer 15 composed of an a-Si film, a channel protective film 16, an n ⁺ a-Si film 17, a Ti film 18, and an Al film are sequentially formed, and the gate insulating film 14 is formed by photolithography. Perform dry etching, drain electrode 19, source electrode 20, and
A bus line (not shown) is patterned.

Next, Si ₃ N _x was placed on the substrate at a substrate temperature of 200 ° C.
The protective film 21 is formed to have a thickness of 350 nm by a low-temperature plasma CVD method for keeping the thickness of the protective film 21, which is not different from the conventional process.

That is, in the pixel forming portion, an auxiliary capacitance electrode 13 is provided on a glass substrate 11, on which a gate insulating film 14 made of Si ₃ N _x and a protective film 21 are laminated. Next, after covering the entire area on the substrate with the resist, only the pixel electrode formation area is opened, and reactive ion etching (abbreviated as RIE) is performed under the following conditions, excluding the protective film 21 and the gate insulating film 14. Al
The auxiliary capacitance electrode 13 was exposed.

Etchant: SF ₆ Flow rate: 200 sccm Gas pressure: 2.6 Pa Power: 800 W Next, a 3% aqueous solution of ammonium borate [(NH ₄ ) ₃ BO ₃ ] is used as an electrolyte, and exposed Al is used as an anode. A platinum (Pt) plate was used as a cathode, constant current formation was performed to increase the voltage to 150 V, and the voltage was maintained at that voltage for 10 minutes, and the surface of the auxiliary capacitance electrode 13 made of Al was aluminum oxide (γ 'Al ₂ O ₃ ) 23.

Here, since the growth rate of aluminum oxide 23 is about 14 ° / V, an Al oxide film having a thickness of 200 nm is grown, and since its relative dielectric constant is about 9, the capacitance is increased. Is equivalent to a conventional device using Si ₃ N _x having a thickness of 700 nm and a storage capacitor electrode having a size of 50 × 90 μm.

That is, the size of the auxiliary capacitance electrode can be reduced to 1/10 and the aperture ratio can be improved. Recently, as a method of improving the aperture ratio, it has been proposed to use a part of a gate bus line as an auxiliary capacitance electrode. However, this method can be similarly applied to this case.

[0036]

According to the present invention, the size of the auxiliary capacitance can be reduced, and the aperture ratio can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a storage capacitor and a TFT according to the present invention.

FIG. 2 is a sectional view of another auxiliary capacitor and a TFT according to the present invention.

FIG. 3 is a sectional view showing a conventional structure of a TFT, a pixel, and an auxiliary capacitor.

FIG. 4 is an equivalent circuit of an active matrix liquid crystal display device.

FIG. 5 is a front view showing an arrangement of TFTs, pixels, and auxiliary capacitors.

[Explanation of symbols]

 3 TFT 4 Source electrode 6 Auxiliary capacitance 7 Pixel 8 Transparent electrode 9,13 Auxiliary capacitance electrode 11 Glass substrate 12 Gate electrode 14 Gate insulating film 21 Protective film 23 Aluminum oxide

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-293329 (JP, A) JP-A-4-44014 (JP, A) JP-A-1-274116 (JP, A) JP-A-4- 274029 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1368

Claims (2)

(57) [Claims] 1. A method for manufacturing a liquid crystal display device comprising a thin film transistor, a pixel electrode, and an auxiliary capacitor formed in a matrix on a substrate, wherein a gate electrode of the thin film transistor is formed on the substrate.
The auxiliary capacitance electrode of the auxiliary capacitance is simultaneously patterned.
And that step, before including a pattern of the gate electrode and the auxiliary capacitance electrode
Forming a gate insulating film on the substrate, and forming an active layer and a source electrode / drain of the thin film transistor.
Forming an in-electrode; forming a protective film covering the thin film transistor ; removing the protective film in the pixel electrode formation region;
Thereby exposing the source electrode and the gate insulating film, Sessu to the source electrode and the gate insulating film is exposed
Forming a pixel electrode, and using the gate insulating film as a dielectric.
You; and a step of forming the storage capacitor
Method of manufacturing a liquid crystal display device. 2. A method for manufacturing a liquid crystal display device comprising a thin film transistor, a pixel electrode, and an auxiliary capacitor formed in a matrix on a substrate, wherein the gate electrode of the thin film transistor is provided on the substrate.
The auxiliary capacitance electrode of the auxiliary capacitance is simultaneously patterned.
And that step, before including a pattern of the gate electrode and the auxiliary capacitance electrode
Forming a gate insulating film on the substrate, and forming an active layer and a source electrode / drain of the thin film transistor.
Forming an in-electrode, forming a protective film covering the thin film transistor, and forming the protective film and the gate insulating film in the pixel electrode formation region
To expose the source electrode and the auxiliary capacitance electrode.
And an oxide film on the surface by electrolytically oxidizing the exposed auxiliary capacitance electrode.
Forming, and a pixel in contact with the exposed source electrode and the oxide film
Forming an electrode and using the oxide film as a dielectric;
Method of manufacturing a liquid crystal display device you; and a step of forming a.