Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2000-11-30
2004-07-27
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
Reexamination Certificate
active
06767775
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, 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 the 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 film includes gate insulation films and interlayer insulation films, and the conductive film is 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-silicone 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)).
However, the silicon film formed by the CVD method have involved some problems which need 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 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.
Handling of highly reactive gaseous silicon hydride to be used as a starting material is difficult, in addition to requiring an air-tight evacuation apparatus as well as a pollutant elimination apparatus for the treatment of exhaust gases. Not only is such a large scale facility itself 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.
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 silicon semiconductor film as described above is usually used as a positive or negative type semiconductor by doping Group III elements or Group V elements in the periodic table. These elements are usually doped by heat diffusion or an ion-injection method after forming the silicon film. Since the heat diffusion method is in principle a high-temperature process (requiring a temperature as high as more than 800° C.), the material available as the substrate is limited. In particular, a glass substrate used for liquid crystal devices is not suitable for the high temperature process. Although the ion-injection method has a feature that impurity distribution toward the depth of the silicon film can be controlled, on the other hand, it is a problem that an evacuation apparatus is necessary besides the apparatus is large in size and heavy as well as expansive.
A dope silicon film in which impurities are doped has been also formed by the CVD method that is used for forming conventional non-dope silicon films. However, this method for forming the dope silicon film involves all the features and problems in the CVD method.
The hot CVD method and plasma CVD method as used in forming the silicon film are also used in forming insulation films such as a gate insulation film and an interlayer insulation film to be used in the thin film transistor. While the insulation film and organic insulation film formed of SOG are frequently used for the purpose of planarization, they are seldom used alone but are used together with the film formed by the CVD method.
The sputtering method is widely used for forming a gate electrode to be used for the thin film transistor, conductive films for the electrode such as source/drain electrodes, a conductive film for wiring lines, and a transparent conductive film to be used for pixel electrodes.
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 which mainly includes 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.
Accordingly, the method for forming the thin film by the conventional CVD method and sputtering method have involved the common 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 f
Seki Shun-ichi
Shimoda Tatsuya
Yudasaka Ichio
Elms Richard
Oliff & Berridg,e PLC
Seiko Epson Corporation
Wilson Christian D.
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