Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from solid or gel state – Using heat
Reexamination Certificate
2000-05-26
2002-10-01
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from solid or gel state
Using heat
C117S008000, C117S009000, C117S200000, C117S204000
Reexamination Certificate
active
06458199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a crystallization apparatus and method for a semiconductor device, and more particularly to a crystallization apparatus and method for crystallizing a semiconductor using the non-vacuum process.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls the light transmissivity of liquid crystal cells in accordance with video signals to display a picture corresponding to the video signals on a liquid crystal panel having the liquid crystal cells arranged in a matrix type. Such a LCD has used thin film transistors (TFTs) as switching devices for selecting pixel cells.
The TFT is classified into an amorphous silicon type and a poly silicon type depending upon whether a semiconductor layer is made from amorphous silicon or poly silicon. The amorphous silicon-type TFT has advantages of a relatively good uniformity and a stable character, whereas it has a drawback of low charge mobility. Also, it has a drawback in that, when the amorphous silicon-type TFT is used, peripheral driving circuits must be mounted onto a display panel after they were separately prepared. On the other hand, the poly silicon-type TFT has an advantage in that, since it has high charge mobility, it is easy to increase the pixel density and peripheral driving circuits can be directly mounted onto a display panel.
The formation of the poly silicon-type TFT is followed by a process of crystallizing an amorphous silicon substrate. In the crystallization process, a laser beam is irradiated mainly within a vacuum chamber so as to reduce a grain boundary.
Referring to FIG.
1
and
FIG. 2
, there is shown a conventional crystallization apparatus that includes a loadlock chamber
2
loaded with a glass substrate
9
, a vacuum chamber
6
for crystallizing the glass substrate
9
, and a transfer chamber
8
provided between the loadlock chamber
2
and the vacuum chamber to transfer a glass. A plurality of glass substrates
9
having been cleaned and dried is disposed within the loadlock chamber
2
. The transfer chamber
8
is provided with a robot arm
4
that is rotary-driven to transfer the glass substrate
9
. The vacuum chamber
6
irradiates laser beams onto the glass substrate
9
to crystallize it. The crystallization process will be described below. The glass substrate
9
transferred into the vacuum chamber
6
by means of the robot arm
4
and safely loaded on a stage
7
is provided with an amorphous semiconductor layer. Laser beams irradiated within the vacuum chamber
6
has a beam profile with Gaussian distribution characteristic as shown in
FIG. 3
, and are irradiated with being overlapped for the purpose of making a fair laser irradiation. When such laser beams are irradiated onto the glass substrate
9
, the glass substrate
9
is changed into a polycrystalline structure by growing grains different in crystalline orientation from the lower surface of the glass substrate
9
while heating it by the laser beams and thereafter cooling it.
In the conventional crystallization apparatus, however, as grains different in crystalline orientation are exploded while the glass substrate
9
is heated by laser beams and then cooled, grain boundaries
9
a
are protruded between the grains as shown in FIG.
4
. Assuming that a thickness of an amorphous semiconductor layer in the glass substrate
9
is 500 Å, the grain boundary
9
a
is protruded into a height of about ±100 Å. Such a grain boundary
9
a
not only causes the generation of a short between electrodes in the course of the process or upon completion of the TFT, but also it causes a crack of the glass substrate
9
by a thermal or physical impact. Accordingly, the crystallization is made within the vacuum chamber
6
maintaining a high vacuum degree so as to reduce the number of grain boundaries
9
a
or the protruded height of the grain boundaries
9
a
, but the grain boundaries
9
a
are not restrained at a satisfying level. Also, the crystallization apparatus of FIG.
1
and
FIG. 2
has problems in that it may be contaminated in a process of transferring the glass substrate
9
by means of the robot arm
4
, and that it is difficult to manage the vacuum degree of each chamber and it undergoes an excessive time waste whenever the glass substrate
9
is transferred by means of the robot arm
4
. In other words, in FIG.
1
and
FIG. 2
, when the glass substrate
9
within the loadlock chamber
2
is moved into the transfer chamber
8
, a gate valve
3
between the loadlock chamber
2
and the transfer chamber is opened or closed. When the glass substrate
9
is transferred into the vacuum chamber
6
by means of the robot arm
4
, a gate valve between the transfer chamber
8
and the vacuum chamber
6
is opened or closed. The conventional crystallization apparatus requires a process of extracting an air from each chamber
2
,
6
and
8
so as to keep the vacuum degree within each chamber
2
,
6
and
8
, particularly within the vacuum chamber
6
after each gate valve
3
and
5
was opened. The throughput is deteriorated due to such an opening or closing operation and such a vacuum degree management of the gate valves
3
and
5
.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a crystallization apparatus and method using a non-vacuum process that is adapted to crystallize a semiconductor in a non-vacuum state.
A further object of the present invention is to provide to a crystallization apparatus and method using a non-vacuum process that is adapted to restrain grain boundaries.
In order to achieve these and other objects of the invention, a crystallization apparatus using a non-vacuum according to one aspect of the present invention includes crystallizing means for irradiating laser beams onto a substrate to grow a crystal unilaterally from the side surface of the substrate.
A crystallization method using a non-vacuum according to another aspect of the present invention includes the steps of irradiating laser beams onto a substrate to grow a crystal unilaterally from the side surface of the substrate.
REFERENCES:
patent: 5612250 (1997-03-01), Ohtani et al.
patent: 6008078 (1999-12-01), Zhang
patent: 6124154 (2000-09-01), Miyasaka
patent: 2001/0000243 (2001-04-01), Sugano et al.
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