Wiring line and manufacture process thereof, and...

Details Wiring line and manufacture process thereof, and... Wiring line and manufacture process thereof, and...

1999-12-16

2003-04-08

Jackson, Jerome (Department: 2827)

Active solid-state devices (e.g., transistors, solid-state diode

Combined with electrical contact or lead

Of specified material other than unalloyed aluminum

C257S761000, C257S763000

Reexamination Certificate

active

06545359

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device including a thin film transistor (TFT) and a device manufacture process thereof, and a contact structure (or a connection structure) of the wiring line in a semiconductor device and a contact forming process thereof. The semiconductor device of the invention includes not only an element such as a thin film transistor (TFT) or a MOS transistor but also a display device including a semiconductor circuit composed of such insulated gate type transistors, and an electrooptical device such as an image sensor. In addition, the semiconductor device of the invention includes an electronic device having such display device and electrooptical device.
2. Related Art
The thin film transistor (as will be called the “TFT”) can be formed over a transparent glass substrate so that its application and development to the active matrix type display device has been positively proceeded. In the active matrix type display device, an electric field to be applied to liquid crystals is controlled in a matrix shape by a plurality of pixels arranged in the matrix shape thereby to realize a highly fine image display. The TFT utilizing a crystalline semiconductor film can achieve a high mobility so that a highly fine image display can be realized by integrating functional circuits over a common substrate.
The active matrix type display device requires more TFTs as many as one million for the pixels as the resolution of the screen becomes finer. If the functional circuits are added, the more TFTs are required to retain the reliabilities and stable actions of the individual TFTs so that the liquid crystal display device may stably act.
The specifications required of the actual liquid crystal display device (as also called the “liquid crystal panel”) are so strict that both the pixels and the drivers have to retain high reliabilities for the normal operations of all pixels. Especially when the driver circuit is troubled, the pixels of one column (or row) cause malfunctions to invite a defect called the “line defect”. If one pixel is troubled, on the other hand, this trouble is called the “point defect”.
Most of the aforementioned line defect and point defect are caused by the malfunctions of the TFTs.
On the other hand, the material used for wiring these TFTs is exemplified by Al, Ta or Ti, of which aluminum having a low resistivity is frequently used. However, aluminum has a low resistance but has a drawback of a low heat resistance.
When the TFT is manufactured by using aluminum as the material for the gate line (including the gate electrode), a projection such as the hillock or whisker has been formed by the heat treatment to cause the malfunction of the TFT or lower the TFT characteristics. On the other hand, the aluminum atoms are caused by the heat treatment to diffuse into a gate insulating film and a channel forming region to cause the malfunction of the TFT or lower the TFT characteristics.
On the other hand, our Unexamined Published Japanese Patent Application No. 7-135318 which corresponds to a U.S. Pat. No. 5,648,277 has disclosed the TFT structure in which the periphery of a gate line is protected with an oxide film (or an alumina film) by using a thin film (as also called the “aluminum alloy”) composed mainly of aluminum as the gate line. When the TFT structure of the Japanese Patent Application is adopted, it is possible to prevent formation of the projection such as the hillock or whisker, but it is difficult to remove a barrier type anodized film (or an anodized film using a neutral electrolyte) formed over a gate electrode and to form a contact between the gate electrode and a lead-out electrode. Therefore, a malfunction is invited by the poor contact between the gate electrode and the lead-out electrode. In the peripheral drive circuit, on the other hand, a temperature rise or the like is caused by a large-current operation so that a reliable contact is also demanded.
On the other hand, the contact can be formed by using a special etchant, as called the “chromium-mixed acid (an etchant prepared by mixing an aqueous solution of chromic acid, phosphoric acid, nitric acid, acetic acid and water) as one for selectively removing only the barrier type anodized film formed over the gate electrode. However, the process using a heavy metal chromium, as may be detrimental to human bodies, is not industrially desirable. On the other hand, the etchant to take place of that chromium-mixed acid is not found at present.
On the other hand, the TFT utilizing a poly-silicon film is still inferior in the reliability to the MOSFET (a transistor formed over a single-crystalline semiconductor substrate) to be used in the LSI. So long as this weak point is not eliminated, moreover, there has been widely accepted a viewpoint that it is difficult to form the LSI circuit with the TFT.
SUMMARY OF THE INVENTION
The invention has been conceived in view of the problems thus far described and has an object to provide a technique for manufacturing a wiring line of a low resistance and a high heat resistance so as to make the active matrix type display device larger and finer.
Another object of the invention is to provide a contact structure which provides an excellent ohmic contact between a first wiring line and a second wiring line without a noxious etchant such as the chromium-mixed acid.
Still another object of the invention is to provide a highly reliable semiconductor device including a semiconductor circuit which has such contact structure and which is formed of TFTs proud of a reliability equivalent to or higher than that of MOSFETs.
In order to solve the above-specified problems, the invention has a main construction in which a gate line (including a gate electrode) made of only aluminum in the prior art is give a laminated structure of a refractory metal, a metal of low resistivity and a refractory metal and in which the gate line is protected by an anodized film. By utilizing the invention, it is possible to form a gate line having a low resistance and a high heat resistance and to form a contact with the gate line easily.
According to a first construction of the invention to be disclosed herein, there is provided a wiring line comprising a multi-layered film in which a first conductive layer, a second conductive layer and a third conductive layer are laminated in the recited order,
wherein the surfaces of the first conductive layer, the second conductive layer and the third conductive layer are oxidized to form oxide films, and
wherein the second conductive layer has a width different from those of the first conductive layer and the third conductive layer.
In the aforementioned construction, the oxide film of the first conductive layer, the oxide film of the second conductive layer and the oxide film of the third conductive layer are of the barrier type.
In each of the aforementioned constructions, on the other hand, the third conductive layer is made of a valve metal.
In the aforementioned constructions, on the other hand, the second conductive layer is made of a material composing aluminum or titanium as its main component.
According to the construction on the manufacture process for practicing the invention, on the other hand, there is provided a process for manufacturing a wiring line, comprising the steps of:
forming a multi-layered film in which a first conductive layer, a second conductive layer and a third conductive layer are laminated in the recited order;
patterning the multi-layered film to form a wiring line; and
anodizing the wiring line;
wherein at the anodizing step, the first conductive layer, the second conductive layer and the third conductive layer are anodized in the same forming solution, and
wherein the second conductive layer has a width different from those of the first conductive layer and the third conductive layer.
The aforementioned construction is characterized in that the wiring line (including an electrode) is constructed of a laminated structure of three or more layers

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