Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from solid or gel state
Reexamination Certificate
2000-06-15
2004-12-14
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from solid or gel state
C117S008000, C117S007000, C117S009000, C117S010000
Reexamination Certificate
active
06830616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a semiconductor film comprising silicon or silicon compound having crystallinity over an insulating surface.
2. Description of the Related Art
A conventional technique is known in which a silicon film is formed over a glass or quartz substrate and a thin-film transistor (hereinafter referred to as “TFT”) is formed by using the thus-formed silicon film.
The TFT is mainly used in the active matrix liquid crystal display device. The TFT is generally classified into the TFT using an amorphous silicon film and the TFT using a crystalline silicon film.
At present, the TFT using an amorphous silicon film is the mainstream. However, the TFT using an amorphous silicon film is low in operation speed and hence its applicability is limited for purposes of reducing the size of a displayed image and displaying a high-speed moving picture.
Further, it is also attempted to constitute, by using TFTs, various circuits that are conventionally implemented as ICs. In this case, the operation speed of the TFT using an amorphous silicon film is much lower than a required value.
In view of the above, the TFT using a crystalline silicon film which is expected to operate at higher speed is now being studied extensively.
Among well known methods for obtaining a crystalline silicon film are:
(1) forming a crystalline silicon film directly by CVD or the like;
(2) crystallizing an amorphous silicon film by a heat treatment;
(3) crystallizing an amorphous silicon film by irradiating it with laser light; and
(4) crystallizing an amorphous silicon film by irradiating it with strong light such as infrared light.
Among the above methods, methods (2)-(4) are mainly used.
Although method (2) is advantageous in that it can easily provide a large-area film, the heat treatment temperature should be high and the quality of a resulting film is insufficient.
Although method (3) is advantageous in that thermal damage does not reach a glass substrate and a film having superior crystallinity can be obtained, it is difficult for method (3) to provide a large-area film and the reproducibility of a process is low.
Although method (4) can easily provide a large-area film, the quality of a resulting film is insufficient.
Studies of the present inventors revealed that the crystallization of an amorphous film can be accelerated by using a metal element typified by nickel (refer to Japanese Unexamined Patent Publication Nos. Hei. 6-232059 and Hei. 7-321339).
By combining the crystallization technique using a metal element with methods (2)-(4), a crystalline silicon film can be obtained that has such high film quality as could not be obtained so far.
However, the crystallinity thus obtained is still insufficient as compared to that of a single crystal silicon wafer and the characteristics of a resulting TFT are far lower than those of a currently available insulated-gate field-effect transistor that constitutes an IC. In particular, there is a serious problem that variations in device characteristics are large.
This is because grain boundaries exist in an uncontrollable state in a crystalline silicon film, i.e., in the channel of a TFT. In particulars since the grain boundaries extending direction cannot be controlled, the device characteristics vary to a large extent due to differences in extending directions of grain boundaries existing in the channels, which necessarily occur when a large number of devices are formed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a technique for obtaining a crystalline silicon film that can provide superior TFT characteristics on a substrate having an insulating surface.
According to one aspect of the invention, there is provided a method for crystallizing at least part of an amorphous film made of silicon or a silicon compound by using a metal element for accelerating crystallization, comprising the steps of introducing the metal element into part of the amorphous film; and forming a temperature gradient in the amorphous film and causing crystal growth from a region where the metal element is introduced to another region by utilizing the temperature gradient.
According to another aspect of the invention, there is provided a method for crystallizing at least part of an amorphous film made of silicon or a silicon compound by using a metal element for accelerating crystallization, comprising the steps of introducing the metal element into part of the amorphous film; and forming a temperature gradient in the amorphous film in a direction extending from a region where the metal element is introduced to another region and causing crystal growth in the temperature gradient direction.
According to a further aspect of the invention, there is provided a method for crystallizing at least part of an amorphous film made of silicon or a silicon compound by using a metal element for accelerating crystallization, comprising the steps of introducing the metal element into part of the amorphous film; and causing the metal element to diffuse in a predetermined direction by utilizing the temperature gradient and causing crystal growth to proceed selectively in the predetermined direction.
In each of the three aspects of the invention, it is preferable to move the temperature gradient in the direction of the crystal growth, to thereby facilitate crystal growth in a direction parallel with the amorphous film.
Crystal growth in a direction parallel with the amorphous film can be facilitated by moving the temperature gradient in the direction of the crystal growth at a speed corresponding to the rate of the crystal growth. This is particularly effective in obtaining a long crystal growth direction.
It is simple and convenient to form the temperature gradient by irradiation with linear infrared light. A means for instantaneously melting and solidifying a surface portion of a silicon film, such as a means using ultraviolet pulse laser light, cannot be used because actually it does not form a temperature gradient.
From the viewpoint of reproducibility and effects, it is preferable to use nickel as the metal element for accelerating the crystallization.
The metal element may be one or a plurality of elements selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir, Pt, and Au.
REFERENCES:
patent: 4001047 (1977-01-01), Boah
patent: 5306022 (1994-04-01), Bourque
patent: 5523262 (1996-06-01), Fair et al.
patent: 5529937 (1996-06-01), Zhang et al.
patent: 5569610 (1996-10-01), Zhang et al.
patent: 5612250 (1997-03-01), Ohtani et al.
patent: 5616506 (1997-04-01), Takemura
patent: 5624851 (1997-04-01), Takayama et al.
patent: 5637515 (1997-06-01), Takemura
patent: 5643826 (1997-07-01), Ohtani et al.
patent: 5712191 (1998-01-01), Nakajima et al.
patent: 5771110 (1998-06-01), Hirano et al.
patent: 5824574 (1998-10-01), Yamazaki et al.
patent: 5837568 (1998-11-01), Yoneda et al.
patent: 5840118 (1998-11-01), Yamazaki
patent: 5932893 (1999-08-01), Miyanaga et al.
patent: 5937282 (1999-08-01), Nakajima et al.
patent: 5956579 (1999-09-01), Yamazaki et al.
patent: 5966594 (1999-10-01), Adachi et al.
patent: 5994172 (1999-11-01), Ohtani et al.
patent: 6051512 (2000-04-01), Sommer et al.
patent: 08-172050 (1996-07-01), None
patent: 9-51099 (1997-02-01), None
patent: 9-51100 (1997-02-01), None
patent: 9-74201 (1997-03-01), None
patent: 9-107108 (1997-04-01), None
patent: 9-237900 (1997-09-01), None
patent: 10-294469 (1998-11-01), None
patent: 2000-82821 (2000-03-01), None
patent: 2000-82822 (2000-03-01), None
Hirano, et al., “Low Temperature Activation method of Poly-Si films using Rapid Thermal Annealing”, vol. 3014, pp. 119-126. Proceedings, Feb. 1997.
Hatalis et al., “Solid phase crystallization of amorphous silicon by rapid thermal processing for flat panel display applications.” Electrochemical Society Proceedings vol. 98-22, pp. 92-99.
Fish & Richardson P.C.
Kunemund Robert
Semiconductor Energy Laboratory Co,. Ltd.
LandOfFree
Manufacturing method of semiconductor and manufacturing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Manufacturing method of semiconductor and manufacturing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Manufacturing method of semiconductor and manufacturing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3319800