Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2000-03-13
2001-12-18
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S030000, C438S592000, C257S610000, C257S611000
Reexamination Certificate
active
06331457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a silicon semiconductor thin film having crystallinity which is formed on a substrate having an insulating surface such as a glass substrate.
2. Description of the Related Art
In recent years, attention has been paid to a technique by which a thin-film transistor is formed using a silicon thin film formed on a glass substrate. The thin-film transistor of this type is mainly used for an active matrix liquid-crystal electro-optical device, and other thin-film integrated circuits. The liquid-crystal electro-optical device is designed such that liquid crystal is sealingly interposed between a pair of glass substrates, and an electric field is applied to the liquid crystal, to thereby change the optical characteristic of the liquid crystal, thus conducting image display.
In particular, the active matrix liquid-crystal display unit using the thin-film transistors is characterized by arranging the thin-film transistors as switches for the respective pixels, and controlling charges held by pixel electrodes. The active matrix liquid display unit is used for the display of a variety of electronic equipments (for example, a portable word processor or a portable computer) because it can display a fine image at a high speed.
An amorphous silicon thin film is generally employed for the thin-film transistor used in the active matrix liquid-crystal display unit.
However, the thin-film transistor using the amorphous silicon thin film suffers from problems stated below.
(1) A higher-quality image display cannot be conducted because the characteristic is low.
(2) A peripheral circuit for driving the thin-film transistor disposed in a pixel cannot be constituted.
The above problem (2) can be classified into two problems one of which is that a CMOS circuit cannot be constituted, since a p-channel type thin-film transistor is not put into practical use for the thin-film transistor using the amorphous silicon thin film, and the other is that the peripheral drive circuit cannot be constituted, since the thin-film transistor using the amorphous silicon thin film cannot conduct high-speed operation and also does not allow a large current to flow therein.
As a method for solving those problems, there is a technique by which a thin-film transistor is formed using a crystalline silicon thin film. As methods for obtaining the crystalline silicon thin film, there are a method for subjecting the amorphous silicon film to a heat treatment, and a method for irradiating a laser light onto the amorphous silicon film.
The method for crystallizing the amorphous silicon film through the heat treatment generally suffers from problems stated below. In order to form the thin-film transistor used in the liquid-crystal electro-optical device, the thin-film transistor is usually required to be formed on a translucent substrate. The translucent substrate may be formed of a quartz substrate or a glass substrate. However, the quartz substrate is expensive and therefore cannot be used in the liquid-crystal electro-optical device which suffers from such a technical problem that the costs must be decreased. Hence, although the glass substrate is generally used, it suffers from such a problem that its heat resistant temperature is low.
It has been proved from the experiment that a temperature of 600° C. or higher is required to crystallize the amorphous silicon film by heating, and also it has been proved from the experiment that several tens hours are required as a heating period. Such a high-temperature and long-period heating cannot be conducted on a large-area glass substrate.
Also, there has been known a technique in which the amorphous silicon film is crystallized by the irradiation of a laser light. However, it is difficult to uniformly irradiate a laser light over a large area of the film, or to irradiate a laser light while maintaining a given irradiation power as a real problem.
SUMMARY OF THE INVENTION
The present invention has been made to eliminate the above problems, and therefore an object of the present invention is to provide a method for manufacturing a semiconductor thin film, which uses the catalytic action of a metal element and manufactures a crystalline silicon film excellent in characteristics.
In order to solve the above problem, the present invention has been achieved by the provision of a method for manufacturing a semiconductor thin film, comprising the steps of:
introducing metal elements into an amorphous silicon film;
crystallizing said amorphous silicon film to obtain a crystalline silicon film;
forming a protective film on said crystalline silicon film;
forming an amorphous silicon film containing impurities therein on said protective film;
diffusing said metal elements in said amorphous silicon film containing the impurities therein; and
removing said amorphous silicon film containing the impurities therein with said protective film as an etching stopper.
In the above method, the amorphous silicon film to be crystallized may be formed of a film which is formed on a glass substrate or a glass substrate on which an insulating film is formed through a plasma CVD method or a low pressure thermal CVD method.
Also, the metal element may be one kind of element or plural kinds of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au. Those metal elements have the catalytic action that promotes the crystallization of silicon, and Nickel (Ni) has the particular catalytic action among those metal elements.
A method for introducing the above metal elements may be a method for forming a layer made of the above-mentioned metal or a layer containing the metal therein on the surface of the amorphous silicon film. Specifically, there are methods for forming a metal-element layer or a layer containing the metal elements therein through the CVD method, the sputtering method, the vapor deposition method or the like, and a method for coating solution containing the metal elements therein on the amorphous silicon film.
However, in case of using the CVD method, the sputtering method, the vapor deposition method or the like, since it is difficult to form a very-thin uniform film, the metal elements non-uniformly exist on the amorphous silicon film, which leads to such a problem that the metal elements are liable to locally exist at the time of crystal growth. On the other hand, the method of using the solution is very preferable, since the concentration of the metal elements can be readily controlled, and the metal elements can be held in uniform contact with the surface of the amorphous silicon film.
In order to crystallize the amorphous silicon film into which the metal elements that promote the crystallization of silicon are introduced, heating may be conducted at a temperature of 450° C. or higher. The upper limit of the heating temperature is limited by the heat resistant temperature of the glass substrate used as a substrate. In case of the glass substrate, the heat resistant temperature can be regarded as a strain point of glass. For example, because a Corning 1737 glass substrate is 667° C. in strain point, the heating temperature can be set to about 620° C., and it is proper from the viewpoints of the heat resistance or the productivity of the glass substrate.
Also, in case of using material that withstands even a temperature of 1,000° C. or higher such as a quartz substrate as a substrate, the heating temperature can be increased in accordance with its heat resistant temperature. In addition, the higher the heating temperature is, the more excellent crystallinity can be obtained for the film.
In the above constitution, the step of forming the protective film may be a step of forming a silicon oxide film, silicon nitride film, and a silicon oxynitride film through the plasma CVD method. Alternatively, there can be applied a step of oxidizing the surface of the crystalline silicon film by the irradiation of UV rays, heating or the like in the air.
The protective film is adapted to f
Miyanaga Akiharu
Ohtani Hisashi
Teramoto Satoshi
Yamazaki Shunpei
Bowers Charles
Fish & Richardson P.C.
Schillinger Laura
Semiconductor Energy Laboratory., Ltd. Co.
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