Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2002-01-31
2003-12-16
Coleman, William David (Department: 2823)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
Reexamination Certificate
active
06664152
ABSTRACT:
CROSS REFERENCE TO RELATED ART
This application claims the benefit of Korean Patent Application No. 1998-40213, filed on Sep. 28, 1998, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for crystallizing a silicon film and a thin film transistor and fabricating method using the same and, more particularly, to a method for crystallizing a silicon film and a method for fabricating a thin film transistor using a laser annealing technique.
2. Discussion of the Related Art
When certain energy, such as laser energy, is applied to amorphous silicon, the amorphous silicon melts and as it cools or solidifies, silicon grains grow and crystallize. Polycrystalline silicon or single crystalline silicon is determined depending on the state of growth of the silicon grain. Single crystalline silicon is obtained in case each silicon grain grows in a single direction and polycrystalline silicon is obtained in case each silicon grain grows randomly at the same time.
For a thin film transistor whose active layer is formed by crystallizing an amorphous silicon film in order to enhance the characteristics of the thin film transistor, it is preferable to reduce the number of grain boundary, which inhibits migration of carriers, by increasing the size of the silicon grain.
FIGS. 1A
to
1
D are schematic diagrams for explaining a method for crystallizing an amorphous silicon film according to related art. Referring to
FIG. 1A
, a first insulation film
11
and an amorphous silicon film
12
are successively deposited on an insulating substrate
10
. An oxide film which exhibits half-reflection is deposited on the amorphous silicon film
12
and then etched by lithography to form a half-reflection layer
13
. Because the half-reflection layer
13
half-reflects an incident laser on the amorphous silicon film
12
, the portion of the amorphous silicon film
12
which underlies the half-reflection layer
13
gets hot fast but cools slowly. Hereinafter, the portion of the amorphous silicon film
12
with the overlying half-reflection layer
13
is called a first silicon region
12
-
1
and the other portion of the amorphous silicon film
12
without the overlying half-reflection layer
13
is called a second silicon region
12
-
2
.
Referring to
FIG. 1B
, a laser beam is irradiated to the entire surface of the substrate
10
. Here, the energy of the laser beam is controlled to such a level that the first silicon region
12
-
1
is completely melted but the second silicon region
12
-
2
contains a predetermined number of unmelted silicon particles
14
.
Referring to
FIG. 1C
, the irradiated amorphous silicon by laser beam is immediately cooled to have the silicon particles grow, thereby, to perform silicon crystallization.
During the crystallization, the silicon particles
14
remaining in the first silicon region
12
-
1
serve as seeds for growing the silicon grains and are grown. The silicon grains stop growing as they collide with one another. Crystallization occurs at many locations of the silicon film at the same time according to the locations of the growth seeds, so that the second silicon region
12
-
2
becomes a first polycrystalline silicon film
15
in which the silicon grains are randomly positioned. In contrast, the first silicon region
12
-
1
remains in a molten state due to the half-reflection layer
13
that retards cooling of the first silicon region
12
-
1
.
Referring to
FIG. 1D
, an interface between the solid first polycrystalline silicon film
15
and the liquid first silicon region
12
-
1
becomes a crystal seed that provides a lateral growth of the grains developing from the boundary of the first polycrystalline silicon film
25
. As a result, a silicon grain boundary is laterally positioned. Here, the silicon grains grown on both boundary sides meet together and stop growing at the center of the first silicon region
12
-
1
. Thus, the first silicon region becomes a second polycrystalline silicon film
16
in which the grains are much larger in size than those of the first polycrystalline silicon film
15
.
However, the silicon grains of the second polycrystalline silicon film
16
obtained in the related art have a size not exceeding a maximum of 1 &mgr;m under the processing atmosphere, at a room temperature or less than 400° C.
When the second polycrystalline silicon film having silicon grains larger than 1 &mgr;m in size is formed, as shown in
FIG. 2
, fine silicon grains are formed at many positions at the center of the second silicon region. Correspondingly, the polycrystalline silicon film crystallized by the related art technique is hard to use for an active layer of thin film transistor, considering that ordinary thin film transistor has a channel length of about 10 &mgr;m.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a silicon film crystallization method and a method for fabricating a thin film transistor using the same.
It is another object of the present invention to provide a silicon film crystallization method by which silicon grains can be dramatically increased in size.
Further, it is another object of the present invention to provide a method for fabricating a thin film transistor with an enhanced characteristic of the device, in which a silicon with silicon grains dramatically increased in size is used as an active layer of the thin film transistor.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve the first object of the present invention, there is provided a method for crystallizing an amorphous silicon film including the steps of: preparing a substrate having the amorphous silicon film, the amorphous silicon film being formed on an intermediate layer which defines an inner space between the substrate and the intermediate layer; and applying an energy to the amorphous silicon film in order to crystallize the amorphous silicon film. The step of preparing the substrate includes the steps of: forming a material layer for forming the space on an insulating substrate, forming the intermediate layer to cover the material layer, forming the amorphous silicon film on the intermediate layer, selectively removing the amorphous silicon film and the intermediate layer to expose a part of the material layer for forming space, and removing the material layer for forming space; or forming a material layer for forming the space on an insulating substrate, forming the intermediate layer to cover the material layer, selectively removing the intermediate layer to expose a part of the material layer, removing the material layer, and forming the amorphous silicon film on the intermediate layer.
In another aspect of the present invention, there is provided a method for fabricating a thin film transistor including the steps of: preparing a substrate having the amorphous silicon film formed on an intermediate layer provided with an inner space at a predefined position thereof; applying a laser energy to the amorphous silicon film to crystallize the amorphous silicon film and form a polycrystalline silicon film; photo-etching the polycrystalline silicon film to form an active layer; forming a gate insulation film and a gate electrode on the active layer; forming a passivation layer covering the exposed entire surface of the substrate including the gate electrode; photo-etching the passivation layer to expose a part of the active layer; and forming source and drain electrodes connected to the exposed active layer.
In another aspect of the present invention, there is provided a thin film transistor including: an insulating substrate; an intermediate layer formed on the insulating sub
Coleman William David
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
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