JPH09266315A - Thin film transistor and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve redundancy and productivity in forming a roll by forming a gate insulating film, a semiconductor layer and source-drain electrodes on the surface of a gate electrode that comprises linear conductor material. SOLUTION: Low resistance such as materials Cu, Al, W, Ta and Al are used for a conductive metal wire 21. A gate insulating film 22, a semiconductor layer 23, a contact layer 24 and a source-drain electrode material 25 are formed on the metal wire so that the metal wire is covered with them. Such as an Si oxide film, an Si nitride film or the lamination of these, or the anodized film of the metal wire are used as the gate insulating film 22, an a-Si:H layer or a poly-Si layer is used as the semiconductor layer 23 and a P doped a-Si:H is used as the contact layer 24. After forming the source-drain electrodes, a resist for separating elements is formed, and after the separation of the element is completed, the resist is peeled off. Then the contact layer is etched to form a source region and a drain region 27 and 28 using the formed source-drain electrode as the mask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor having a completely new structure and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Thin film transistors are used in liquid crystal display devices and image sensors. Here, FIG. 1 shows a conventional array substrate structure of an active matrix type liquid crystal display device. 1A and 1B are a plan view and a cross-sectional view of one pixel of the array substrate, respectively. Pixel electrodes and thin film transistors for controlling pixel potentials are formed on the array substrate. The thin film transistor is a field effect transistor including a gate electrode 16 and source / drain electrodes 22. After forming the gate electrode 16 on the glass substrate 14, a gate insulating film 17 and a semiconductor layer 18 are sequentially formed to deposit a film forming a thin film transistor. A silicon oxide film or a silicon nitride film is used as the gate insulating film 17,
As the semiconductor layer 18, hydrogenated amorphous silicon (a-
Si: H) is used. The deposition temperature of such a film is PE-C.
VD (Plasma Enhanced-Chemical Vapor Deposition)
The temperature of the substrate 14
The feature is that glass can be used as. We have succeeded in significantly lowering the temperature as compared with the thin film transistor manufacturing process using crystalline silicon or polysilicon.

However, in general, when heat is applied to the glass substrate 14, the glass substrate 14 is deformed by thermal contraction. The heat shrinkage deteriorates the alignment accuracy of the patterning. For example, after forming the gate pattern, the gate insulating film 17 and the semiconductor layer 1 are formed.
8. When depositing the channel protection layer 19, etc.
Increase the temperature from ℃ to 400 ℃. Thermal contraction occurs due to the temperature rise of the substrate 17. When the substrate deformation due to heat shrinkage is large, the pattern of the channel protection layer against the pattern of the gate electrode
Cannot be properly aligned. In order to solve the alignment problem due to the heat shrinkage of the substrate, a glass substrate having a large strain point must be used. In this sense, it was necessary to select a glass substrate for the liquid crystal display device.

Depending on the size of the substrate and the alignment accuracy, heat shrinkage may not be a problem. However, even in this case, impurities diffused from the glass pose a problem. For example,
Various impurities are added in manufacturing glass. Impurities in these glasses diffuse according to the process temperature, and diffuse into the film forming the thin film transistor on the substrate. In particular, alkali ions such as Na behave as mobile ions, have a great influence on the threshold variation of the thin film transistor, and deteriorate the reliability of the pixel potential switching element such as the thin film transistor. Therefore, it is not possible to use low-cost soda lime glass or the like, and it is necessary to use low-alkali glass or non-alkali glass.

In order to solve the above-mentioned problems of heat shrinkage and impurity diffusion, it is necessary to select a glass substrate having a low content of impurities or to lower the process temperature. Glass having a low content of impurities is generally expensive, which increases the cost of the liquid crystal display device. On the other hand, lowering the process temperature means deteriorating device characteristics such as thin film transistors. When the film formation temperature is lowered, generally the electric defect level in the film is increased and the film quality is deteriorated. In this sense, the process temperature cannot be easily lowered.

Further, as a specification of a future liquid crystal display substrate, lightness and impact resistance are required. For example, portable terminals and document viewers are essential hardware for future multimedia development. Since these devices are portable, lightweight and impact resistance are essential. Also,
In large displays, the increase in substrate weight cannot be ignored due to the increase in substrate size. Therefore, it is desirable to use a substrate such as plastic having a low specific gravity as the display substrate.

The plastic substrate causes thermal decomposition and thermal deformation at a lower temperature than glass due to its composition. The heat resistance of the transparent plastic substrate used for the transmissive liquid crystal display device is generally 200 ° C. or less. Therefore, using a plastic substrate, the deposition temperature is about 200 to 400 ℃, a-Si: H
It is difficult to manufacture an active matrix type liquid crystal display device using a thin film transistor of polysilicon or polysilicon.

An active matrix type liquid crystal display device using thin film transistors is a simple matrix, MIM.
The display quality is generally higher than that of other display methods such as an active matrix using an element. In this sense, future displays will require active matrices using FET-type thin film transistors. However, since it is necessary to use a high temperature process to manufacture a thin film transistor, usable substrate materials are limited.

Furthermore, the number of manufacturing steps of the thin film transistor is larger than that of other methods. For example, the liquid crystal display element using the thin film transistor shown in FIG. 1 has a considerably larger number of steps than in the case of an MIM type two-terminal element or a simple matrix type display device. Considering the decrease in yield due to process abnormalities, the smaller the number of array substrate processes, the higher the productivity in general. In this sense, a liquid crystal display device using a thin film transistor can obtain a high quality image, but its productivity is inferior to that of other systems because of the large number of steps. In a liquid crystal display device using a thin film transistor, the finest processing is required to form the thin film transistor. About 10 6 thin film transistors are formed in a 9 inch display.
A display device having no display defect means that all thin film transistors operate normally. If the thin film transistor is over the limit, it is necessary to discard the whole substrate.

Further, in the prior art, when manufacturing liquid crystal display devices having different diagonal sizes, even if the thin film transistors have the same shape, it is necessary to provide a photomask suitable for the diagonal size to be manufactured. That is, when the thin film transistor shape used in the 9-inch class liquid crystal display device and the thin film transistor shape of the 12-inch class liquid crystal display device are the same,
It was wasteful because it was necessary to change the size of the photomask according to the size of the substrate to be created and remake it according to all products.

[0011]

Since the conventional thin film transistor is formed directly on the substrate which is the material to be the base to be formed, there are many restrictions on the types of substrates that can be used.
Further, since the thin film transistor is formed on the substrate, if a defect occurs in the intermediate process or the final process, the entire substrate is discarded and the productivity is poor, which causes a cost increase. Further, even if the same thin film transistor structure is provided, it is necessary to prepare a photomask in all cases according to the diagonal size of the display device.

The present invention has been made in view of the above problems, and provides a new type thin film transistor and liquid crystal display device which enables a plurality of substrates to be used on any substrate without increasing the cost and which does not require a complicated manufacturing process. The purpose is to do.

[0013]

In order to achieve the above object, the invention of claim 1 provides a gate electrode made of a linear conductive material, a gate insulating film formed on the surface of the gate electrode, and A thin film transistor comprising a semiconductor layer formed on a gate insulating film and source / drain electrodes formed on the semiconductor layer with a space therebetween.

According to a second aspect of the present invention, in the first aspect, the gate insulating film, the semiconductor layer, and the source / drain electrodes are coaxial with the center of the conductive material so as to cover the conductive material. The present invention provides a thin film transistor characterized by being formed thereon.

Further, according to a third aspect of the present invention, an array substrate having a pixel electrode and a switching transistor for driving the pixel electrode formed on an insulating surface, and a common electrode on a surface facing the substrate are arranged. In a liquid crystal display device comprising a counter substrate on which the switching substrate is formed and a liquid crystal layer formed between the array substrate and the counter substrate, the switching transistor is formed in a groove formed on the surface of the array substrate. A gate electrode made of a linear conductive material, a gate insulating film formed on the surface of the gate electrode, and a semiconductor layer formed on the gate insulating film,
A liquid crystal display device comprising a source / drain electrode formed separately on the semiconductor layer.

The invention of claim 4 provides the switching transistor according to claim 3, wherein the switching transistor has the conductivity so that the gate insulating film, the semiconductor layer, and the source / drain electrodes cover the conductive material. The present invention provides a liquid crystal display device, which is formed coaxially with the center of the material.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment of the Invention) A method of manufacturing a thin film transistor on a wire will be specifically described with reference to FIGS. In the figure, (a) is a sectional view taken along a plane parallel to the center of the metal wire, and (b) is a sectional view taken along a plane perpendicular to the center. As the conductive metal wire 21, low resistance Cu, Al, W, Ta, Au wire or the like is used. For the metal wire 21, as shown in FIG.
The gate insulating film 22, the semiconductor layer 23, the contact layer 24 and the source / drain electrode material 25 are formed so as to cover the metal wires. As the gate insulating film 22, for example, a silicon oxide film, a silicon nitride film, a stacked layer thereof, an anodized film of a metal wire, or the like may be used. Further, an a-Si: H layer, a polysilicon layer, or the like may be used as the semiconductor layer 23. As the contact layer 24, P-doped a-Si: H or the like may be used. These films need not be concentric and may be eccentric as long as a short circuit between layers does not occur. Further, the cross section may be polygonal.

Next, after forming the source / drain electrodes as shown in FIG. 5, a resist 26 for element isolation is formed. After the element isolation is completed, the resist is removed.
The contact layer is etched using the source / drain electrodes formed next as a mask, and the source and drain regions 2
7 and 28 are formed.

(Second Embodiment of the Invention) FIG. 7 shows an embodiment in which the thin film transistor of the present invention is used in a liquid crystal display device.
A metal wire 31 having a plurality of thin film transistors formed therein is embedded in a grooved substrate 32 in the row direction. At this time, the thin film transistors on the metal lines need to be formed at intervals that match the pitch of the pixel electrodes. A pixel electrode 33 for display is formed in the embedded thin film transistor, and is formed in the column direction with respect to the metal line 31 in which the signal line electrode is embedded to form an active matrix type array substrate. The metal line plays a role of a gate electrode and controls ON / OFF of the thin film transistor. The thin film transistor serves as a switching transistor that applies a voltage to the pixel electrode.

A method of manufacturing a liquid crystal display device using the thin film transistor thus manufactured will be described more specifically.
As shown in FIG. 8, a metal wire 41 having a plurality of thin film transistors formed thereon is fixed to a substrate having a groove 42 in advance as illustrated. The groove 42 may be mechanically formed or formed by photolithography.

Next, although not shown, a display electrode material is deposited on the substrate and a desired pixel electrode structure is patterned.
At this time, it is formed so as to be connected to the drain electrode of the thin film transistor by, for example, overlapping.

Next, although not shown, a signal line material is deposited by a sputtering method or the like, and a metal line 51 provided with a thin film transistor is formed.
The deposited signal line material is subjected to etching so as to be perpendicular to, to form a signal line, and the signal line and the source electrode are connected. In order to form a contact pad of a metal line corresponding to the gate line, it is necessary to partially etch the gate insulating film and form a contact hole before depositing the signal line material. Through the above steps, the array substrate shown in FIG. 7 is produced. A liquid crystal is interposed between the array substrate and a counter substrate having a transparent electrode formed on the entire surface thereof to complete a liquid crystal display device.

The characteristics of the thin film transistor of the present invention are as follows. As shown in the application to the liquid crystal display device described above, it is not necessary to raise the substrate temperature. No temperature increase is required to deposit the pixel electrode material or signal line material. Even when it is necessary to raise the temperature, the deposition temperature of the display electrode material and signal line material is about 100 ° C, which is lower than the conventional maximum process temperature. Since the thin film transistor manufacturing process, which requires a high temperature process to obtain good characteristics, is completed on the metal line, it does not affect the substrate temperature. A thin film transistor / active matrix type liquid crystal display device can be manufactured without raising the substrate temperature, and the selection range of the substrate material used is expanded. In particular, it enables the use of a light-weight and impact-resistant substrate such as a plastic substrate. Further, since the thin film transistor having a large number of steps is not formed on the substrate, the productivity of the array substrate is improved.

Next, the method of forming a wire-shaped thin film transistor is simpler than the conventional method. As described above, the number of patterns of the thin film transistor is two, so that the number of conventional steps can be significantly reduced. The pattern formation method is also easier than before. In the past, patterning required a photomask matching the substrate size. That is, even in panels having the same thin film transistor structure, if the diagonal size is different, it is necessary to remake a mask matching the diagonal size. However, in the thin film transistor of the present invention, it is not necessary to remake the photomask in accordance with the display area. For example, as shown in FIG. 9, when it is desired to selectively form a resist pattern in the portion of the switching element 51, only an exposure device having a slit as shown in FIG. 10 is required.

The patterning process will be specifically described below. A resist is applied on the metal wire and the film covering the metal wire, and a metal wire 62 forming a thin film transistor is passed through a pipe 61 shown in FIG. A slit as shown in FIG. 10 is formed in the pipe 61. The metal wire 62 is fixed at the portion where exposure is required, and the slit light is irradiated with the exposure light 63. The metal wire 62 is sequentially sent to expose a desired portion. If the exposure apparatus has a plurality of such slits, the exposure can be carried out in a batch, so that the efficiency is improved. By repeating this operation, it is possible to form a plurality of thin film transistor patterns along the metal line.
If the structure of the thin film transistor is determined, it is not necessary to match the panel size and mask to be used. Furthermore, when changing the pattern shape, such as changing the channel length, it is only necessary to change the slit width. For example, when it is desired to shorten the channel length of the thin film transistor, it can be dealt with only by shortening the slit width.

Wet processes such as etching and development can be easily and continuously performed as shown in FIG. Etching can be continuously performed by sequentially passing the metal wire 72 on which the thin film transistor is formed through a bath filled with the etchant 71. Further, similarly, washing may be carried out through a water tank. Alternatively, as shown in FIG. 12, it may pass through the inside of the shower.

As described above, the thin film transistor of the present invention is characterized in that it can be formed as a roll independent of the substrate used. Therefore, not only the liquid crystal display device,
The productivity of device manufacturing that requires an array of thin film transistors can be improved. In particular, the feature is that the limitation on the film forming temperature is widened.

(Embodiment 3 of the Invention) FIG. 16 is a sectional view of a thin film transistor. The feature is that the channel protective film layer 94 is formed on the semiconductor layer 93. Since the channel protective layer 94 is formed, the semiconductor layer 93 can be thinned. In FIG. 16, when the contact layer is etched to form the source / drain region 97 composed of the contact layer 95 and the metal electrode, the contact layer 95 is n + a-Si: H, the semiconductor layer 93 is a-Si: H, or the like. In this case, it is necessary to increase the thickness of the a-Si: H film because there is no etching selectivity. Therefore, there is a problem that the throughput is reduced. By using a film having a high selectivity for n + a-Si: H, it is possible to realize a thin semiconductor layer.

A specific manufacturing method will be described with reference to FIGS. On the wire 91, the gate insulating film 92, the semiconductor layer 93,
The channel protection layer 94 is deposited. As wire, Cu,
Al, W, Ta, Au wire or the like is used. As the gate insulating film, a silicon oxide film, a silicon nitride film, a laminated film thereof, or an anodized film of wire metal is used. As a semiconductor layer
a-Si: H, polysilicon or the like is used. A silicon oxide film, a silicon nitride film, or the like is used as the channel protective layer.

Next, the channel protective layer is patterned as shown in FIG. The size of this pattern determines the channel length L and channel width of the thin film transistor. After patterning, the contact layer 95, for example P-doped n + a-S
i: H and microcrystalline silicon are deposited (FIG. 16).

Subsequently, the source / drain electrode material 96 is deposited. Mo, Al, or a laminated film of these may be used as the electrode material. Finally, as shown in FIG. 17, the electrode material 96 is patterned, and the formed pattern is used as a mask to form the semiconductor layer 93.
Then, the contact layer 95 is etched to perform element isolation. Next, a gap 1 is formed in the source / drain metal 96,
Contact layer 95 using the source / drain electrodes as a mask
To etch. As described above, the thin film transistor shown in FIGS. 17A and 17B can be obtained.

[0032]

The thin film transistor can be formed on a conductive wire material to form a thin film transistor roll,
Low cost. Furthermore, this expands the range of substrate materials that can be used, and further improves redundancy and productivity. Further, since the high temperature process can be applied, the device characteristics can be improved as compared with the conventional low temperature process.

[Brief description of drawings]

FIG. 1 is a plan view of one pixel of a conventional liquid crystal display device.

FIG. 2 is a cross-sectional view of one pixel of a conventional liquid crystal display device.

FIG. 3 is a sectional view of the thin film transistor according to the first embodiment of the present invention.

FIG. 4 is a sectional view of the thin film transistor according to the first embodiment of the present invention.

FIG. 5 is a sectional view of the thin film transistor according to the first embodiment of the present invention.

FIG. 6 is a sectional view of the thin film transistor according to the first embodiment of the present invention.

FIG. 7 is a perspective view of a thin film transistor on an array substrate according to a second embodiment of the present invention.

FIG. 8 is a sectional view showing a manufacturing process of a thin film transistor according to a second embodiment of the present invention.

FIG. 9 is a diagram illustrating a second embodiment of the present invention.

FIG. 10 is an explanatory diagram of an exposure method used for manufacturing the thin film transistor according to the embodiment of the present invention.

FIG. 11 is a diagram illustrating a manufacturing method according to an embodiment of the present invention.

FIG. 12 is a diagram illustrating a manufacturing method according to an embodiment of the present invention.

FIG. 13 is a sectional view of a thin film transistor according to a third embodiment of the present invention.

FIG. 14 is a sectional view of a thin film transistor according to a third embodiment of the present invention.

FIG. 15 is a sectional view of a thin film transistor according to a third embodiment of the present invention.

FIG. 16 is a sectional view of a thin film transistor according to a third embodiment of the present invention.

FIG. 17 is a sectional view of a thin film transistor according to a third embodiment of the present invention.

[Explanation of symbols]

 21 conductive metal wire 22 gate insulating film 23 semiconductor layer 24 contact layer 25 source / drain electrode material 26 resist 27, 28 source / drain region

Claims (4)

[Claims] 1. A gate electrode made of a linear conductive material,
A gate insulating film formed on the surface of the gate electrode, a semiconductor layer formed on the gate insulating film, and source / drain electrodes formed separately on the semiconductor layer. Thin film transistor. 2. The gate insulating film, the semiconductor layer, and the source / drain electrodes are formed coaxially with the center of the conductive material so as to cover the conductive material. Item 3. The thin film transistor according to Item 1. 3. An array substrate having a pixel electrode and a switching transistor for driving the pixel electrode formed on an insulating surface, and a counter substrate having a common electrode formed on the surface facing the substrate and facing the substrate. A switching element formed in a groove formed on the surface of the array substrate and having a linear conductivity. A gate electrode made of a material, a gate insulating film formed on the surface of the gate electrode, a semiconductor layer formed on the gate insulating film, and source / drain electrodes formed separately on the semiconductor layer. A liquid crystal display device comprising: 4. The switching transistor is formed coaxially with the center of the conductive material so that the gate insulating film, the semiconductor layer, and the source / drain electrodes cover the conductive material. The liquid crystal display device according to claim 3, wherein