Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2000-11-30
2003-02-04
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S166000
Reexamination Certificate
active
06514801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing thin film transistor to be used for liquid crystal display devices, auto-luminescent display devices and LSIs. In more detail, the present invention relates to a method for manufacturing a thin film transistor by forming a thin film constituting the thin film transistor using a liquid material.
2. Description of Related Art
A thin film transistor is usually composed of thin films such as semiconductor films, insulation films and conductive films. When these thin films are categorized depending on their functions, the insulation films include gate insulation films and interlayer insulation films, and the conductive films are used for gate electrodes, source/drain electrodes, pixel electrodes and wiring lines. These thin films have been mainly deposited by a CVD (Chemical Vapor Deposition) method and a sputtering method.
Silicon films such as amorphous silicon films and poly-silicon films have been mainly used for the semiconductor films. The silicon films have been usually formed by a thermal CVD method, a plasma CVD method or a photo-CVD method using monosilane gas or disilane gas. The thermal CVD method has been generally used for depositing the poly-silicon film (J. Vac. Sci. Technology, vol. 14, p1082 (1977)), while the plasma CVD method has been widely used for depositing the amorphous silicon (Solid State Com., vol. 17, p1193 (1975)).
SUMMARY OF THE INVENTION
The silicon film formed by the CVD method have involved some problems to be improved in the manufacturing process: (1) manufacturing yield is low due to contamination of the manufacturing apparatus and generation of foreign substances, since silicon particles appear in the gas phase to be used for the gas phase reaction, (2) a silicon film with a uniform thickness cannot be deposited on a substrate having a rough surface, since a gaseous starting material is used, (3) a step for heating the substrate is required, and productivity is low due to a slow deposition rate of the film, and (4) a complicated and expensive microwave generator and an evacuation apparatus are necessary in the plasma CVD method.
Handling of highly reactive gaseous silicon hydride to be used as a starting material is difficult, besides requiring an air-tight evacuation apparatus as well as a pollutant elimination apparatus for the treatment of exhaust gases. Not only such large scale facility itself is expensive, but also a large amount of energy is consumed in the vacuum system and plasma system, rendering the product a high manufacturing cost.
A method for coating liquid silicon hydride that is free from the vacuum system has been proposed in recent years. Japanese Unexamined Patent Application Publication No. 1-29661 discloses a method for forming a silicon thin film by allowing a gaseous material to be liquefied and absorbed on a chilled substrate as a liquid, followed by allowing the substrate to react with chemically active atomic hydrogen. However, the method also involves a problem that a complicated apparatus is required for continuously evaporating and liquefying silicon hydride, and control of the film thickness is difficult (1).
While Japanese Unexamined Patent Application Publication No.7-267621 discloses a method for coating the substrate with low molecular weight liquid silicon hydride, on the other hand, handling of this complex system is so troublesome that it is difficult to obtain a uniform film thickness when applied to a large area substrate.
While an example of a solid silicon hydride polymer has been reported in UK Patent GB-2077710A, it is impossible to form a film by coating since the compound is insoluble in solvents.
The thermal CVD method, plasma CVD method and sputtering method have been widely used for forming a gate insulation film used for thin film transistors, an insulation film for the interlayer insulation firm, and an electrode conductive film for the gate electrode and source/drain electrodes. The conductive film to be used for the thin film transistor is used for the gate electrode source/drain electrodes wiring lines for connecting among the electrodes, and wiring lines for a power circuit, and a metal film such as Al, Cu, Cr or Ta film is used as the conductive film. The conventional sputtering method is widely used for forming the metal film and siliside film. While a transparent conductive film in addition to the foregoing conductive film is required for the thin film transistor to be used for a liquid crystal display device, an ITO film is usually used for the transparent conductive film, which is deposited by the sputtering method as used in forming the metal film.
The CVD method involves the following four features, which are the same as those in forming the silicon film as an insulation film: (1) manufacturing yield is low due to contamination of the manufacturing apparatus and generation of foreign substances, since silicon particles appear in the gas phase to be used for the gas phase reaction, (2) a silicon film with a uniform thickness can not be deposited on a substrate having a rough surface, since a gaseous starting material is used, (3) a step for heating the substrate is required, and productivity is low due to a slow deposition rate of the film, and (4) a complicated and expensive microwave generator and an evacuation apparatus are necessary in the plasma CVD method.
An evacuation apparatus, in addition to a vacuum pump as well as a target material, a sputtering power source and a substrate heating apparatus, are required for the sputtering method to be utilized in forming the conductive film mainly comprising a metal film and the transparent conductive film. Although a toxic and combustible gas is seldom used in the sputtering method as compared with the CVD method, the film is deposited not only on the substrate as a film deposition object but also on the inner wall of the chamber in which the substrate is placed. Peeled pieces of the deposition material from the inner wall serve as foreign substances during the film deposition process to result in decreased manufacturing yield of the product as in the CVD method. It is the common drawbacks of the sputtering method with the CVD method that the film thickness is uneven at the rough portions on the surface of the substrate, productivity is low, and the facilities become large scale and expensive because an evacuation apparatus is required.
The method for forming the thin film by the conventional CVD method and sputtering method have involved the problems of low productivity, high incidence of film defects and low yield, uneven film thickness at the rough surface portions, and breakage of wiring patterns at the steps. These problems also cause increased manufacturing cost of the thin film transistor. These problems in the CVD method and sputtering method arise from intrinsic features of the film deposition method such as use of the evacuation apparatus, need of heating of the substrate, requirement of a power source for plasma generation, and film deposition on unnecessary portions such as the inner wall of the apparatus other than the substrate. These intrinsic features arise other problems that the large scale apparatus leads to a high facility cost, and the running cost of the apparatus is also high.
The present invention proposes a method for manufacturing a thin film transistor by a novel method essentially different from the conventional film deposition method. While the thin films such as a silicon film and an insulation film in the thin film transistor have been deposited by a CVD method or a sputtering method, a desired thin film is formed in the present invention by coating a substrate with a liquid material to form a coating film, followed by heat-treating the coating film.
The object of the present invention is to provide a method for solving the intrinsic problems involved in the conventional film deposition method, providing a method for manufacturing a thin film transistor with a low manufacturing cost using a com
Seki Shun-ichi
Shimoda Tatsuya
Yudasaka Ichio
Dang Phuc T.
Nelms David
Oliff & Berridg,e PLC
Seiko Epson Corporation
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