Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from solid or gel state – Using heat
Reexamination Certificate
1999-03-22
2002-04-16
Nguyen, Kiet T. (Department: 2881)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from solid or gel state
Using heat
C117S010000, C438S487000, C438S488000
Reexamination Certificate
active
06372039
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same, and a laser irradiation device, and more particularly to a method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor and a pulse laser irradiation device.
The thin film transistor has an active layer of a polycrystal silicon thin film formed on a glass substrate. The thin film transistor may be used for the liquid crystal display and the contact image sensor or other electronic devices. A laser anneal method has been often used in view of reduction in process temperature and improvement in throughput. A silicon thin film is once formed as a precursor and then an ultraviolet ray pulse laser beam is irradiated onto the silicon thin film for causing crystallization to polycrystalline structure. It is widely used that a linear pulse laser beam is scanned in a width direction perpendicular to the line direction.
The conventional laser beam irradiation method has a problem in low uniformity. An influence of a pulse laser beam edge of the previously irradiated pulse laser beam causes a large variation in crystal grain diameters to be formed in the next laser beam irradiation. A melting state of the thin film by the laser beam irradiation depends upon the thin film crystal structure before the laser beam irradiation. Particularly, when amorphous silicon thin film is used as a precursor, a remarkable variation in melting state may appear on a boundary between the crystal region already irradiated with the laser beam and the amorphous region unirradiated with the laser beam.
FIG. 1A
is a diagram illustrative of a variation in energy density over position of a pulse laser beam with a top flat energy density profile to be irradiated onto an amorphous silicon thin film for annealing the same.
FIG. 1B
is a diagram illustrative of a distribution in crystal grain size over position of a polycrystalline region formed by irradiation of a pulse laser beam with the energy density profile of
FIG. 1A
onto the amorphous silicon thin film.
FIG. 1C
is a diagram illustrative of a change of distribution in crystal grain size over position of the polycrystalline region by scanning at a pitch “x” the pulse laser beam, wherein the crystal grain size has a minimum size value in the vicinity of the laser beam of FIG.
1
B.
FIG. 1D
is a diagram illustrative of a final distribution in crystal grain size over position of the polycrystalline region after scanned at a pitch “x” the pulse laser beam, wherein the crystal grain size varied over position.
FIG. 2A
is a diagram illustrative of a variation in energy density over position of a pulse laser beam with a top flat energy density profile to be irradiated onto an amorphous silicon thin film for annealing the same wherein a maximum energy density is beyond a micro-crystallization threshold value of the polysilicon film.
FIG. 2B
is a diagram illustrative of a distribution in crystal grain size over position of a polycrystalline region formed by irradiation of a pulse laser beam with the energy density profile of
FIG. 2A
onto the amorphous silicon thin film.
FIG. 2C
is a diagram illustrative of a change of distribution in crystal grain size over position of the polycrystalline region by scanning at a pitch “x” the pulse laser beam, wherein the crystal grain size has a minimum size value in the vicinity of the laser beam of FIG.
2
B.
FIG. 2D
is a diagram illustrative of a final distribution in crystal grain size over position of the polycrystalline region after scanned at a pitch “x” the pulse laser beam, wherein the crystal grain size varied over position.
In Japanese laid-open patent publication No. 9-219380, it is disclosed that in order to improve the uniformity of crystal grain size of the polysilicon thin film, a pulse laser beam having a step-like energy density profile is irradiated onto the amorphous silicon thin film. Even the irradiation of the pulse laser beam having the step-like energy density profile onto the amorphous silicon thin film causes variation or change in crystal grain size at the beam edge positions, for which reason it is difficult to obtain the required uniformity in crystal grain size of the polysilicon region.
In the above circumstances, it had been required to develop a novel method of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from the above problem, and a laser irradiation device.
method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor and a pulse laser irradiation device.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel method of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from the above problems.
It is a further object of the present invention to provide a novel method of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from any influence of a pulse laser beam edge previously irradiated.
It is still a further object of the present invention to provide a novel method of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same to obtain a uniformity in crystal grain size.
It is yet further object of the present invention to provide a novel device of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from the above problems.
It is a further more object of the present invention to provide a novel device of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same free from any influence of a pulse laser beam edge previously irradiated.
It is still more object of the present invention to provide a novel device of irradiation of a laser onto a non-single crystal semiconductor thin film for annealing the same to obtain a uniformity in crystal grain size.
It is moreover object of the present invention to provide a novel method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor free from the above problems.
It is another object of the present invention to provide a novel method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor free from any influence of a pulse laser beam edge previously irradiated.
It is still another object of the present invention to provide a novel method of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor to obtain a uniformity in crystal grain size.
It is yet another object of the present invention to provide a novel device of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor free from the above problems.
It is further another object of the present invention to provide a novel device of irradiation of a pulse laser onto a polycrystal semiconductor thin film for forming an active layer of a polycrystal silicon thin film transistor used for a liquid crystal display and a contact image sensor free from any influence of a pulse laser beam edge previously irradiated.
It is an additional object of the present invention to provide a novel device of irradiation of a pu
Okumura Hiroshi
Tanabe Hiroshi
Nguyen Kiet T.
Young & Thompson
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