Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2000-09-12
2004-08-03
Lee, Eddie (Department: 2811)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S479000, C438S517000, C257S347000
Reexamination Certificate
active
06770515
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device that has an active region of a crystalline silicon film obtained by crystallizing an amorphous silicon film and a method for fabricating the device. The present invention is effective, in particular, for a semiconductor device that employs a thin film transistor (TFT) provided on a substrate having an insulating surface and is able to be utilized for an active matrix type liquid crystal display device, a contact-type image sensor, a three-dimensional IC and the like.
In recent years, there have been attempts to form a high-performance semiconductor device on an insulating substrate of glass or an insulating film for the achievement of a large-size high-resolution liquid crystal display device, a high-speed high-resolution contact-type image sensor, a three-dimensional IC and the like. It is general to use thin-film-shaped silicon semiconductors as semiconductor elements for use in these devices. The silicon semiconductors can be roughly categorized into the two types of an amorphous silicon semiconductor (a-Si) and a silicon semiconductor having crystallinity.
The amorphous silicon semiconductor, which can be relatively easily fabricated by the vapor deposition method at a low fabricating temperature and suitable for mass production, is most generally used. However, the amorphous silicon semiconductor has inferior physical properties of electrical conductivity and so on with respect to the silicon semiconductor having crystallinity. Therefore, in order to obtain a higher-speed characteristic, it is strongly demanded to establish a method for fabricating a semiconductor device made of a silicon semiconductor having crystallinity. As a silicon semiconductor having crystallinity, there are known polysilicon, microcrystal silicon, amorphous silicon including a crystalline component and semi-amorphous silicon having a state intermediate between the crystalline property and the amorphous property.
As a method for obtaining a silicon semiconductor having crystallinity, there are known the following methods (1) through (3).
(1) A method for directly forming a film having crystallinity in a film-forming stage
(2) A method for forming an amorphous semiconductor film and crystallizing the film by the energy of laser light
(3) A method for forming an amorphous semiconductor film and crystallizing the film by applying thermal energy
However, according to the aforementioned method (1), crystallization progresses concurrently with the film forming process. Therefore, in order to obtain a silicon film having crystals of a large grain size, it is indispensable to increase the thickness of the silicon film. It is technically difficult to uniformly form a silicon film having satisfactory semiconductor properties thoroughly on the entire surface of the substrate.
According to the aforementioned method (2), which utilizes the crystallization phenomenon through a melting and solidifying process, the grain boundaries are satisfactorily processed although the grain size is small, allowing a high-quality crystalline silicon film to be obtained. However, taking the excimer laser, which is currently most generally used, as an example, it is difficult to uniformly process the entire surface of a large-area substrate since the laser stability is not sufficient.
According to the aforementioned method (3), which is advantageous in terms of uniformity and stability inside the substrate by comparison with the methods (1) and (2), is used for a microminiature high-definition LCD panel employing a quartz substrate. However, in this case, after growing crystals through heat treatment at a temperature of 600° C. for a long time of about 30 hours, the crystals are further subjected to heat treatment at an high temperature of about 1000° C. for several tens of minutes to several hours for the promotion of improvement in crystallinity, and this results in a prolonged processing time and a degraded throughput. If a TFT is fabricated with this crystallized silicon film, then only the device characteristic of a field effect mobility of about 100 cm
2
/Vs can be obtained.
In order to solve the aforementioned problems, a method of an improvement of the aforementioned method (3) is disclosed in Japanese Patent Laid-Open Publication No. HEI 7-335905. This Japanese Patent Laid-Open Publication No. HEI 7-335905 discloses a reduction in heating temperature, a reduction in processing time and an improvement in crystallinity by utilizing a catalytic element that promotes the crystallization of the amorphous silicon film.
Specifically, a trace quantity of a metallic element of nickel, palladium or the like is introduced into the surface of the amorphous silicon film, and thereafter heat treatment is performed. With regard to the mechanism of low-temperature crystallization, the generation of a crystalline nucleus occurs in the early stage with the metallic element serving as the nucleus. Subsequently, the metallic element serves as a catalyst to promote the crystal growth for the rapid promotion of the crystallization, according to the understanding. In this sense, the aforementioned metallic element is referred to as a “catalytic element” hereinafter. By comparison with the twin crystal structure in one particle of the crystalline silicon film crystallized by the normal solid phase epitaxy, the crystalline silicon film that has undergone crystal growth with the catalytic element forms an aggregate of a number of columnar crystals, each of which has an almost ideal monocrystalline internal state.
According to the method of the aforementioned Japanese Patent Laid-Open Publication No. HEI 7-335905, crystals grow sidewise (in a direction parallel to the substrate) from the region into which the catalytic element is introduced by crystallizing only the region into which the catalytic element is selectively introduced with the other portion remaining in a state of an amorphous silicon film through selective introduction of the catalytic element into part of the amorphous silicon film and heating of the same and further prolonging the heating time.
Furthermore, according to the method of the aforementioned Japanese Patent Laid-Open Publication No. HEI 7-335905, the sidewise crystal growth distance is increased by forming the amorphous silicon film that is the start film to be crystallized by the low pressure CVD method, and the active region of the thin film transistor is formed by using the sidewise crystal growth region.
In contrast to this, the Japanese Patent Laid-Open Publication No. HEI 7-307286 discloses another example of the use of the catalytic element, or the use of the catalytic element for dehydrogenation in the amorphous silicon film.
Specifically, the dehydrogenating reaction in the amorphous silicon film is promoted by introducing the catalytic element into the amorphous silicon film containing hydrogen and heating the film at a low temperature of not higher than 550° C., and thereafter, the amorphous silicon film is crystallized by laser light application. The dehydrogenation in the amorphous silicon film is thus promoted and thereafter the amorphous silicon film is crystallized by laser light application. Therefore, the film exfoliation is hard to be caused by rapid dehydrogenation of the silicon film even if the laser light application is performed, and a crystalline silicon film having uniform crystallinity is obtained.
As disclosed in the aforementioned Japanese Patent Laid-Open Publication No. HEI 7-335905 and the Japanese Patent Laid-Open Publication No. HEI 7-307286, the crystalline silicon film obtained by introducing the catalytic element into the amorphous silicon film and crystallizing the film through heat treatment is excellent in terms of crystallinity. In particular, the crystal orientation is closer to the conventional monocrystal than the polycrystal. Through confirmation with a TEM (Transmission Electron Microscope), the present inventor has obtained a distinct diffraction pattern that exhibits a monocrystal state ev
Makita Naoki
Moriguchi Masao
Gebremariam Samuel A
Lee Eddie
Sharp Kabushiki Kaisha
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