JPH06265936A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the gate insulating film parts and capacitors of TFTs having the small specific resistance of electrodes and the specific dielectric constant of insulating films functioning as dielectric and to provide the liquid crystal display device which is formed by using these elements and has high characteristics. CONSTITUTION:The gate electrode 5 of the TFT 2 is formed by alternately laminating, for example, tantalum layers 51 and aluminum layers 52 on a transparent insulating substrate 4 consisting of glass, etc. The first gate insulating film 6a consists of a laminate of a tantalum pentaoxide (Ta2O5) layer 61 formed by anodizing a tantalum layer 51 on the surface of the gate electrode 5 and an aluminum layer 52 and an aluminum oxide (Al2O3) layer 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device.
More specifically, a gate insulating film of a thin film transistor (hereinafter, referred to as a TFT) that switches each pixel and an insulating film serving as a dielectric of an auxiliary capacitor for holding a voltage of a pixel electrode are 2
The present invention relates to a liquid crystal display device including a laminate of metal oxide films of at least one kind.

[0002]

2. Description of the Related Art In a liquid crystal display device, two transparent substrates are adhered to each other at a constant gap so that they are parallel to each other, and a liquid crystal layer is sandwiched between the two transparent substrates.

Pixel electrodes are provided in a matrix on opposite surfaces of two transparent substrates, and a TFT 2 for switching the pixel electrode 1 and a pixel electrode 1 are further provided on one transparent substrate as shown in FIG. An auxiliary capacitance (hereinafter, referred to as a capacitor) 3 for holding the voltage applied to is provided.

Of these, in the TFT 2, a gate insulating film 6 having a two-layer structure of a gate electrode 5, a first gate insulating film 6a and a second gate insulating film 6b is provided on a transparent insulating substrate 4 such as glass. A semiconductor layer 7 made of amorphous silicon, polysilicon, or the like, which serves as a functional layer, is sequentially formed and formed. The amorphous silicon on the semiconductor layer 7 including the p ⁺ -type or n ⁺ -type conductivity type impurity with a predetermined gap, and a source region 8a and drain region 8b of the same conductivity type made of a semiconductor layer such as polysilicon A source electrode 9a and a drain electrode 9b made of aluminum or the like are provided on these regions respectively. In addition, 10 is a protective film.

Further, the capacitor 3 is formed by sequentially laminating a lower electrode 11, an insulating film 12 having a two-layer structure of a first insulating film 12a and a second insulating film 12b which are dielectrics, and an upper electrode 13. Has been done. The upper electrode 13 is formed integrally with the pixel electrode 1 serving as a display screen by a transparent conductive film made of, for example, ITO, tin oxide, indium oxide or the like.

As described above, the gate insulating film 6 of the TFT 2
Recently, the insulating film 12 of the capacitor 3 is formed in a two-layer structure from the viewpoint of improving reliability and yield, and one of them is a metal oxide film obtained by anodic oxidation of an electrode film. In this case, since the gate electrode 5 and the lower electrode 11 are formed of a single layer such as aluminum or tartar, the first gate insulating film 6a and the first insulating film 12 are formed.
Each a is made of aluminum oxide (Al ₂ O ₃ ) or tantalum pentoxide (Ta ₂ O ₅ ) formed by, for example, anodizing the gate electrode 5 and the lower electrode 11. Further, the second gate insulating film 6b and the second insulating film 12b are formed of, for example, silicon nitride by a plasma CVD method or the like.

Since the above-mentioned anodic oxidation is performed in a solution, it is possible to suppress the occurrence of defects during film formation due to particles which are impurities found in a dry thin film forming process such as a plasma CVD method. Therefore, an insulating film that becomes the gate insulating film 6 of the TFT 2 and / or the dielectric of the capacitor 3
As described above, when 12 has a two-layer structure of, for example, a silicon nitride film and a metal oxide film, a short circuit in the insulating film can be prevented and the yield can be improved.

In order to satisfy the conditions that the metal oxide film formed by anodic oxidation is a dense film and has a high withstand voltage and little deterioration in film quality even after long-term use, the base metal to be anodized is used. Is limited, and as described above, tantalum (including an alloy of tantalum) or aluminum (including an alloy of aluminum) is generally used.

[0009]

In the TFT 2 which constitutes the liquid crystal display device, for example, the gate electrode 5 also serves as the gate signal wiring for the sake of simplifying the manufacturing process, so that the propagation time of the gate pulse can be shortened. Therefore, it is preferable to use a material having a small specific resistance. This is more and more necessary because the signal wiring becomes longer as the screen size of the liquid crystal display panel becomes larger and the signal wiring becomes thinner as the pixel becomes finer. From this point of view, it is preferable to use aluminum, which has a smaller specific resistance than tantalum, as the metal forming the gate electrode 5. By the way, the specific resistance is about 4 Ω · cm for aluminum and about 25 Ω · cm for tantalum.

On the other hand, TFT2 which is a MOS transistor
In the above, since the gate insulating film 6 functions as the dielectric of the capacitor composed of the gate electrode 5 and the semiconductor layer 7, the first gate insulating film formed by anodizing the surface of the gate electrode 5 is used. The film 6a is preferably made of tantalum pentoxide, which has a higher relative dielectric constant than aluminum oxide. From this point of view, it is preferable to use tantalum for the gate electrode 5 in order to downsize the TFT and improve the aperture ratio of the liquid crystal display device. By the way, the dielectric constant of Al ₂ O ₃ is about 9.2, Ta ₂ O ₅ is about 25, and SiN
_x is about 6.7.

However, in the conventional TFT, since the gate electrode 5 is made of a single metal of either tantalum or aluminum, a TFT having a low specific resistance of the electrode and a high relative dielectric constant of the dielectric cannot be obtained. There's a problem.

Further, light metals such as aluminum and heavy metals such as tantalum are generally difficult to alloy due to the difference in lattice constant. On the other hand, it is possible to form the gate electrode 5 with tantalum and the gate signal wiring with aluminum, but in this case, there is a problem that the number of lithography processes increases in the manufacturing stage, the yield decreases, and the manufacturing cost increases. is there.

The lower electrode 11 of the capacitor 3 and the first insulating film 12a have the same problem as the TFT.

The present invention has been made in order to solve such a problem, and it is possible to obtain a TFT or a capacitor in which the specific resistance of the electrode is small and the relative dielectric constant of the insulating film functioning as a dielectric is large, and An object of the present invention is to provide a high-performance liquid crystal display device using an element.

[0015]

A liquid crystal display device according to the present invention is an active matrix type liquid crystal display device having a switching thin film transistor and an auxiliary capacitor for each pixel, the gate insulating film of the thin film transistor and / or the above At least a part of the insulating film of the auxiliary capacitance is made of an oxide of two or more kinds of metal films.

Further, the capacitor according to the present invention is a capacitor in which an insulating film is sandwiched between electrodes, and at least one of the electrodes is formed of a part of a laminate of two or more kinds of metal films, and at least one of the insulating films is formed. The part is made of an oxide of at least two kinds of metal films of the laminate.

Further, the TFT according to the present invention is a thin film transistor in which a gate electrode, a gate insulating film, and a semiconductor layer are sequentially laminated on an insulating substrate, and at least two kinds of the gate insulating film are provided on the gate electrode side. It is composed of an oxide of a metal film.

[0018]

According to the present invention, the gate electrode of the TFT and /
Alternatively, since the lower electrode of the capacitor is made of a laminated body of two or more kinds of metal thin films, the advantages of different metals can be combined and the specific resistance of the electrode can be reduced.

Further, since the gate insulating film and / or the insulating film serving as the dielectric of the capacitor is formed by oxidizing the laminated body, it is possible to combine the advantages of different metal oxides, and the relative permittivity is increased. It is possible to form an insulating film that is large and has no pinholes and good insulation.

Further, the gate insulating film and / or the insulating film serving as the dielectric of the capacitor, the metal thin films are laminated in units of several tens to several hundreds of Å, so that they are uniformly oxidized and are stable laminated oxide films. Becomes

[0021]

The present invention will be described below with reference to the drawings.

FIG. 1 is an enlarged view of an essential part of an embodiment of the gate insulating film of the TFT of the present invention, FIG. 2 is an explanatory view of the manufacturing process of the gate insulating film shown in FIG. 1, and FIG. 3 is a liquid crystal display device. FIG. 6 is a cross-sectional explanatory view showing a state where a TFT and a capacitor are formed on one transparent substrate.

In the liquid crystal display device of the present invention, as shown in FIG. 3, a TFT 2, a pixel electrode 1 and a capacitor 3 for auxiliary capacitance are formed on one transparent substrate 4, and an alignment film (not shown) is further provided. After being provided, the other transparent substrate (not shown) is also provided with an electrode film, an alignment film and the like.
Liquid crystal material (not shown) glued at a constant gap with
Are formed by filling the gaps.

In the present invention, the gate electrode 5 and the gate insulating film 6a portion of the TFT 2, the electrode 11 of the capacitor 3 and the insulating film are formed.
The 12a portion is characteristic, and the structure of the insulating film will be described first.

As shown in FIG. 1, for example, in the case of TFT, the gate electrode 5 is a transparent insulating substrate 4 such as glass.
The tantalum layer 51 and the aluminum layer 52 having a thickness of about 50 to 500 Å are alternately laminated on the upper surface to form a thickness of about 500 to 5000 Å.
Tantalum pentoxide (Ta ₂ O ₅ ) layer 61 and aluminum oxide (Al ₂ O ₃ ) layer formed by anodizing the tantalum layer 51 and the aluminum layer 52 in the range of about 300 to 3000 Å from the surface of It consists of a laminate with 62. A second gate insulating film 6b (shown by a chain double-dashed line in FIG. 1) made of, for example, silicon nitride and having a thickness of about 1500 to 3000Å is provided on the first gate insulating film 6a. ing. In addition, in FIG. 1, a laminated body including six layers is shown for convenience, but the number of laminated layers is not limited to six layers in the embodiment and the present invention.

Even if an insulating film is formed by an oxidation method by stacking materials having different oxidation rates and characteristics such as tantalum and aluminum, a metal having a high oxidation rate (for example, aluminum) is oxidized to the inside and a metal having a low oxidation rate is used. Oxidation of (for example, tantalum) does not proceed, and a uniform insulating film cannot be obtained. However, by forming a stack of thin metal films of about 50 to 500 Å for each metal film, even a metal with a low oxidation rate is promoted to oxidize from a metal with a high oxidation rate above and below, and a uniform oxide film can be obtained. Is found.

Next, the manufacturing process of the insulating film of the present invention will be described with reference to FIG. 2 by taking the gate insulating film of the TFT as an example.

First, as shown in FIG. 2 (a), thin films of different kinds of metals are sequentially laminated on an insulating substrate 4 such as glass by a sputtering method or a vacuum evaporation method, and then etched and patterned to form a gate. The electrode 5 is formed. Specifically, the tantalum layer 51 and the aluminum layer 52 having a uniform thickness of 50 to 500 Å are alternately formed by the sputtering method for about 2 to 2
After 10 layers were stacked, the gate electrode 5 was formed by the RIE method using a mixed gas in which chlorine and fluorine were mixed at an appropriate ratio to adjust the etching rate of the tantalum layer 51 and the aluminum layer 52 to 1.

Next, as shown in FIG. 2B, the surface of the gate electrode 5 is anodized, and the first gate insulating film 6 is formed on the surface.
a is formed. Specifically, in a mixed solution of tartaric acid, ammonia, and ethylene glycol having a temperature of about 20 to 100 ° C and a concentration of about 2 to 10% by weight, the gate electrode 5 is used as an anode, and platinum or palladium is used as a cathode between both electrodes. A voltage was applied. At this time, so that anodization is performed at an appropriate speed,
The current value and the voltage value are finely controlled, the surface of the gate electrode 5 is oxidized to a range of about 300 to 3000 Å, and the first gate insulating film 6a made of a stack of a tantalum pentoxide layer 61 and an aluminum oxide layer 62 is formed. Formed. Although the tantalum layer 51 is less likely to be oxidized than the aluminum layer 52, the aluminum layer 52 and the tantalum layer 51 are about 50 to 500 as described above.
Since the layers are alternately laminated with a thickness of Å, in the tantalum layer 51, active oxygen permeates not only from the surface and side surfaces of the gate electrode 5 but also from the vertically adjacent aluminum layers 52. As a result, the tantalum layer 51 and the aluminum layer 52 are apparently oxidized at the same oxidation rate. After the anodic oxidation, a dense first gate insulating film 6a is obtained by performing an annealing treatment for about 1 hour in an air atmosphere of about 200 to 350 ° C., for example.

On the other hand, when the thickness of each layer of the laminated body composed of the aluminum layer 52 and the tantalum layer 51 exceeds about 500 Å, the permeation of active oxygen from the aluminum layer 52 into the tantalum layer 51 causes the tantalum layer 51 to penetrate. Since it takes time to reach the center of the thickness, the oxidized state of the gate electrode 5 is not uniform, and the first gate insulating film 6a having a uniform film quality cannot be obtained.

If the temperature can be raised to about 400 to 500 ° C., plasma-assisted dry anodic oxidation can be used instead of the above-mentioned wet anodic oxidation. Then, after the anodic oxidation, an annealing treatment is performed in a hydrogen atmosphere at a temperature of about 450 ° C. for about 40 minutes, for example. As a result, residual stress in the first gate insulating film 6a and the gate electrode 5 is removed.

Next, as shown in FIG. 2C, a second gate insulating film 6b is further formed on the above-mentioned first gate insulating film 6a. Specifically, silicon nitride having a thickness of about 1500 to 3000 μm was formed by the plasma CVD method. Thus, the gate insulating film 6 having a two-layer structure is completed.

In the description of FIGS. 1 and 2, the gate insulating film of the TFT is taken as an example, but the lower electrode 11 of the capacitor is used.
The same applies to the structure of the insulating film 12 and the manufacturing method thereof, and it goes without saying that not only a capacitor used for liquid crystal display or the like but also a capacitor having a general dielectric film sandwiched between electrodes can be similarly formed.

Generally, light metals such as aluminum and heavy metals such as tantalum have different lattice constants and are difficult to alloy, but they are periodically laminated with a film thickness of several tens to several hundreds of Å, especially a film thickness equal to or smaller than the crystal grain size of the metal. As a result, interference that acts between dissimilar metals, such as contact and residual stress, is mitigated, and when anodizing is performed, the difference in the diffusion coefficient of the oxidizing species and the difference in the expansion coefficient between the metals are apparently mitigated. , Evenly oxidized,
A stable metal oxide film can be obtained.

In the above embodiment, the case where two kinds of metals are alternately laminated has been described, but three or more kinds of different metals may be sequentially laminated.

[0036]

According to the present invention, since an insulating film is formed by oxidizing a part of a plurality of kinds of metal film laminates, electrical characteristics such as relative permittivity and pinholes are less likely to occur. An insulating film having both insulating properties can be obtained, and a gate and a capacitor of a TFT having a low specific resistance of electrodes and wiring can be obtained. Moreover, it is possible to obtain a high yield without increasing the number of masks in the lithography process.

Therefore, it is possible to achieve miniaturization of the TFT and the capacitor, and it is possible to obtain a liquid crystal display device having a fast switching operation and a large aperture ratio when applied to a liquid crystal display device.

[Brief description of drawings]

FIG. 1 is an enlarged view of a main part of an embodiment of a gate insulating film of a TFT of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process of the gate insulating film shown in FIG.

FIG. 3 is a cross-sectional explanatory view showing a state in which a TFT and a capacitor are formed on one transparent substrate of a liquid crystal display device.

[Explanation of symbols]

 2 TFT 3 capacitor 4 insulating substrate 5 gate electrode 6 gate insulating film 6a first gate insulating film 6b second gate insulating film 7 semiconductor layer 11 lower electrode 12 insulating film 12a first insulating film 12b second insulating film 13 Upper electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiro Hata 21 No. 21, Mizozaki-cho, Saiin, Ukyo-ku, Kyoto City ROHM Co., Ltd.

Claims (3)

[Claims] 1. An active matrix liquid crystal display device having a switching thin film transistor and an auxiliary capacitor for each pixel, wherein at least a part of a gate insulating film of the thin film transistor and / or an insulating film of the auxiliary capacitor is of two types. A liquid crystal display device comprising the oxide of the above metal film. 2. A capacitor having an insulating film sandwiched between electrodes, wherein at least one of the electrodes is formed of a part of a laminate of two or more kinds of metal films, and at least a part of the insulating film is the laminate. A capacitor comprising an oxide of at least two kinds of metal films. 3. A thin film transistor comprising a gate electrode, a gate insulating film, and a semiconductor layer sequentially stacked on an insulating substrate, wherein at least the gate electrode side of the gate insulating film is made of an oxide of two or more kinds of metal films. Thin film transistor.