Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2002-08-08
2004-08-24
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S150000, C438S149000
Reexamination Certificate
active
06780692
ABSTRACT:
This application claims priority to Japanese Patent Application Number JP2001-242774 filed Aug. 9, 2001 which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a laser annealing apparatus for applying an annealing treatment to a material by irradiating the surface of the material with laser light, and a method of fabricating a thin film transistor by converting an amorphous silicon film to a polycrystalline silicon film which becomes an active layer of the thin film transistor through an annealing treatment.
The thin film transistor is widely used as a switching device in a liquid crystal display. Where polycrystalline silicon (hereinafter referred to as polysilicon) film is used as a channel layer in the thin film transistor, the electrolytic mobility of the thin film transistor is very high, so that the thin film transistor can be incorporated, for example, as a driving circuit in a liquid crystal display, and it is possible to realize higher definition, smaller size and the like of the display.
In addition, the thin film transistor using a polysilicon film as the channel layer has a higher driving current, as compared with the case where an amorphous silicon film is used as the channel layer, so that the thin film transistor can be applied to a pixel transistor in an organic electroluminescence (hereinafter abbreviated to EL) display utilizing EL of an organic material using a current driving system.
As a method for forming a polysilicon film on an insulating substrate, there is a method of converting an amorphous silicon film formed on the surface of an insulating substrate formed of, for example, glass, quartz, etc. into a polysilicon film by subjecting the amorphous silicon film to a laser annealing treatment through irradiation with laser light by use of a laser annealing apparatus.
The laser annealing apparatus used for the laser annealing treatment uses an excimer laser as a light source of the laser light. The excimer laser emits laser light at an ultraviolet wavelength in a pulsed state, and, since silicon has a high absorption coefficient for the laser light at the ultraviolet wavelength emitted in the pulsed state, an efficient laser annealing treatment of an amorphous silicon film can be achieved.
The laser annealing treatment is conducted in such a manner that the laser light emitted from the excimer laser is processed by, for example, a beam homogenizer to form the irradiation plane relative to the amorphous silicon surface into a linear form, and the amorphous silicon is polycrystallized into polysilicon while moving the irradiation region of the laser light. At the time of performing the laser annealing treatment, the laser light is scanned in a direction orthogonal to the longitudinal direction of the irradiation plane of the laser light formed in the linear form.
In the laser annealing apparatus described above, however, the pulsed emission of the laser light from the excimer laser is performed through excitation of an excitable gas such as XeCl and KrF, so that the emission of the laser light will easily become unstable attendant on deterioration of the excitable gas, and the light intensity of the laser light on a pulse basis may be dispersed.
In this laser annealing apparatus, therefore, the laser annealing treatment of the amorphous silicon film is conducted with the laser light dispersed in light intensity, resulting in a laser annealing treatment in which the heated and molten state of the amorphous silicon film is dispersed.
Therefore, with the amorphous silicon film of which the heated and molten state is dispersed, the grain size of crystal grains in the polysilicon film obtained through recrystallization is dispersed. Thus, there has been the problem that nonuniformity in the form of, for example, streaks or spots, is generated in the picture formed by display devices, and transistor characteristics are deteriorated.
In addition, in the laser annealing apparatus as above, the step of gas replacement attendant on the deterioration of the excitable gas used in the excimer laser leads to a lowering in productivity and an increase in the cost of production of the thin film transistor.
Furthermore, the laser annealing apparatus needs a tank for storing the excitable gas, and is large in the size of equipment. Therefore, the laser annealing apparatus leads to a large installation area and a large power consumption, resulting in an increase in the cost of production of the thin film transistor.
SUMMARY OF THE INVENTION
The present invention has been proposed in consideration of the above situations. Accordingly, it is an object of the present invention to provide a laser annealing apparatus capable of an annealing treatment with stable light intensity, and a method of fabricating a thin film transistor which makes it possible to enhance transistor characteristics, to enhance productivity and to reduce production cost by using a polycrystalline silicon film obtained through the annealing treatment by laser light with the stable light intensity.
In accordance with one aspect of the present invention, there is provided a laser annealing apparatus for subjecting a material to an annealing treatment by irradiating the surface of the material with laser light, comprising a plurality of semiconductor laser devices for emitting laser light toward the material, and unformizing means for uniformizing the light intensity of the laser light emitted from the plurality of semiconductor laser devices and radiated to the surface of the material.
In the laser annealing apparatus, the laser light emitted from the plurality of semiconductor laser devices is processed by the uniformizing means so that the light intensity of the laser light with which the surface of the material is irradiated is uniformized, to that it is possible to subject the material to an annealing treatment by the laser light with a stable light intensity.
According to the present invention, therefore, dispersion of the heated and molten state of the amorphous silicon film can be restrained, the grain diameter of crystal grains of the polycrystalline silicon film recrystallized from the amorphous silicon film is uniformized, and transistor characteristics of the thin film transistor comprising the polycrystalline silicon film as an active layer can be enhanced.
In accordance with another aspect of the present invention, there is provided a method of fabricating a thin film transistor which comprises a first step of forming an amorphous silicon film on a substrate, a second step of subjecting the amorphous silicon film to an annealing treatment to thereby convert the amorphous silicon film into a polycrystalline silicon film, and a third step of laminatingly fabricating the thin film transistor in a predetermined region with the polycrystalline silicon film as an active layer. In the method of fabricating a thin film transistor, in the second step, the laser annealing apparatus comprising a plurality of semiconductor laser devices for emitting laser light subjects the surface of the amorphous silicon film to the annealing treatment while uniformizing the light intensity of the laser light radiated onto the surface of the amorphous silicon film by uniformizing means for uniformizing the light intensity of the laser light radiated onto the surface of the amorphous silicon film, whereby the amorphous silicon film is heated, melted and recrystallized to be thereby converted into the polycrystalline silicon film.
According to the method of fabricating a thin film transistor, the laser annealing apparatus subjects the amorphous silicon film to the annealing treatment while processing the laser light emitted from the plurality of semiconductor laser devices by the uniformizing means so as to uniformize the light intensity of the laser light with which the surface of the amorphous silicon film is irradiated. Therefore, dispersion of the heated and molten state of the amorphous silicon film is restrained, the grain diameter of the crystal grains of the polycrystal
Eguchi Naoya
Tatsuki Koichi
Tsukihara Koichi
Depke Robert J.
Holland & Knight LLP
Kennedy Jennifer M.
Niebling John F.
Sony Corporation
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