Optical: systems and elements – Lens – Including a nonspherical surface
Reexamination Certificate
1999-06-04
2001-01-09
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Including a nonspherical surface
C219S121750, C219S121670, C219S121720
Reexamination Certificate
active
06172820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser irradiation device, and more particularly to a laser irradiation device irradiating a linear laser beam whose length in the major axis can be altered using a lens optical system.
2. Description of the Related Art
Recently, a liquid crystal display (hereinafter, referred to as an “LCD”) has been developed using polysilicon (hereinafter, referred to as “p-Si”) as a material of switching elements, although amorphous silicon (hereinafter, referred to as “a-Si”) was widely used before. In order to form or promote the grain growth of the p-Si, an annealing process using a laser beam is adopted.
FIG. 1
is a conceptual diagram showing a laser irradiation device for performing the laser annealing.
In
FIG. 1
, numeral
1
denotes a laser generator, numerals
2
and
11
denote reflection mirrors, numerals
3
,
4
,
5
and
6
denote cylindrical lenses, and numerals
7
,
8
,
9
,
12
and
13
denote condenser lenses. Numeral
10
is a slit that defines the linear width direction of the laser beam irradiated on a substrate. A stage
14
supports the substrate
20
to be processed, on which an a-Si film is formed, and can be moved in the x and y directions.
The laser beam irradiated from the laser generator
1
has an energy distribution in the beam plane. The difference of the energy levels in the beam plane brings about a difference of annealing condition for the a-Si, which generates a variation of the film quality of the p-Si formed by the polycrystalline process depending on the location in the p-Si film. In order to eliminate such a defect, the energy level of the laser beam should be as flat as possible in the beam plane. In the device shown in
FIG. 1
, the laser beam is split in the horizontal and the vertical directions with respect to the optical center using a pair of cylindrical lenses
3
and
5
, as well as a pair of cylindrical lenses
4
and
6
. The vertically split beams are condensed by the condenser lenses
8
,
9
,
12
and
13
and focused in one direction (the vertical direction) as shown in FIG.
2
. Thus, the energy variation of the beam is canceled in the vertical direction. At the same time, the horizontally split laser beams are condensed by the condenser lens
7
so as to cancel the energy variation and enlarged in one direction (the horizontal direction) as shown in FIG.
3
. In this way, passing the cylindrical lenses
3
-
6
, the condenser lenses
7
-
9
,
12
and
13
, the laser beam is focused in one direction and enlarged in the other direction in the irradiation plane. Thus, the laser beam becomes a linear laser beam having substantially uniform energy level in each direction in the plane, which is irradiated toward the substrate
20
to be processed. The stage
14
on which the substrate
20
is placed can be scanned by the irradiated linear laser in the linear width direction. By this scanning in the linear width direction, the annealing process can be performed for a large area. Thus, laser annealing process with high throughput can be achieved by this device.
Here, the linear longitudinal direction means the direction of the major axis of the laser beam, while the linear width direction means the direction of the minor axis of the laser beam.
FIG. 4
shows laser beam irradiation toward a mother glass substrate
30
for making multiple TFT substrates
31
on which TFT's including p-Si as an active layer are arranged, as an LCD panel on the large glass substrate
30
.
On the mother glass substrate
30
, a-Si is deposited and the linear laser beams
32
and
33
are irradiated scanning in the scan direction, thereby causing the a-Si to be polycrystallized to become p-Si.
However, in the conventional laser irradiation device the optical system is fixed, so the area of the linear laser beam irradiated on the substrate is fixed. Especially, since the length of the linear laser beam irradiated on the substrate in the linear longitudinal direction (the major axis direction) is fixed, there is a problem as explained below.
Each size of the plural TFT substrates
31
formed on one mother substrate
30
is determined as desired, e.g., as 2.5 inches or 3 inches by diagonal size. Therefore, if the size of the mother glass substrate, which is a to-be-processed substrate
20
, or the size of the TFT substrate formed on the mother substrate changes, the laser irradiation device cannot be used anymore, which is not rational from the viewpoint of cost.
In addition, if a laser irradiation device having improper length of the linear line is used, when irradiating the laser beam toward the mother glass substrate
30
on which the TFT substrates
31
are arranged as shown in
FIG. 4
, for example, the whole surface of the fourth TFT substrate
31
cannot be irradiated from above in the figure by the first scan of the laser beam
32
. Therefore, the fourth TFT substrates
31
is required to be irradiated by the second laser beam irradiation
33
overlaying the first irradiated area. Then, an area
35
is generated that is irradiated by both the first and second scans of the laser beam on the fourth TFT substrate
31
. In this case, since the laser irradiation condition is different between the area
35
and other area, the grain size of the polycrystalline semiconductor film may be uneven within the fourth TFT substrate
31
. In addition, characteristics of each TFT substrate
31
on the mother glass substrate
30
may be varied.
In order to prevent each of the irradiated laser beams from overlaying each other on a certain TFT substrate, a space
35
may be disposed for each block of the TFT substrates corresponding to the length in the major axis of the linear laser beam as shown in FIG.
5
. However, this measure may cause another problem such that limitation in the size of each substrate would occur, for example, the mother substrate is required to be enlarged, or the size of the TFT substrate should be decreased. At the same time, this measure can cause decreasing number of TFT substrates that can be produced from one mother substrate, and increase of the manufacturing cost.
SUMMARY OF THE INVENTION
In view of the foregoing conventional problem, an object of the present invention is to provide a laser irradiation device that can irradiate a laser beam uniformly on the whole surface of various size of TFT substrates.
In order to achieve the above-mentioned object, a laser irradiation device of the present invention includes an optical system forming the linear laser beam extending in one direction from the laser beam emitted by a laser generator. The optical system has at least a pair of adjustment lenses being in charge of adjustment of the laser beam in the direction corresponding to the major axis direction of the linear laser beam. The distance between the pair of adjustment lenses is adjustable.
In another aspect of the present invention, the distance between the pair of adjustment lenses is realized by making at least one of the adjustment lenses movable in the optical axis direction within the optical path using a position adjustment mechanism.
Further in the above-mentioned aspect, one of the adjustment lens having more flexibility of location in the optical path than the other can be moved by the position adjustment mechanism. Thus, the distance between the pair of adjustment lenses can be changed easily with minimum change to the optical system.
In another aspect of the device according to the present invention, the device has a condenser lens for condensing the incident laser beam after passing the pair of adjustment lenses and for enlarging the incident laser beam in the major axis of the linear laser in accordance with the incident width (l
hw
).
In still another aspect of the present invention, adding to the above-mentioned condenser lens, a slit is disposed between the condenser lens and the object to be irradiated, for interrupting the edge region of the laser beam emitted from the condenser lens. Since a low energy region is generated in the edge r
Epps Georgia
Hogan & Hartson LLP
Sanyo Electric Co,. Ltd.
Thompson Tim
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