JPH0851074A - Manufacture of polycrystalline semiconductor film - Google Patents

Abstract

PURPOSE:To restrain a region which is not enough in crystal uniformity from increasing in a polycrystalline semiconductor film by a method wherein the semiconductor film is irradiated with a sheet-like pulsed laser beam which has two different energy intensity distributions, one is high enough in intensity for crystallization at its center along a major axis and the other is not enough in intensity for crystallization along a minor axis. CONSTITUTION:A sheet-like beam which has two different energy intensity distributions, one is high enough in intensity for crystallization through all area or at its center along a major axis and the other is like a trapezoid along its minor axis. That is, the energy distribution along the minor axis is lower than a certain energy distribution required for crystallization and another energy level required for crystallizing a preceding region in a beam scanning direction and increases gradually in intensity. By this setup, a region which is not enough in crystal uniformity can be restrained from increasing in a polycrystalline semiconductor film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polycrystalline semiconductor film.

[0002]

2. Description of the Related Art In recent years, various techniques for improving the performance of thin film transistors, which are driving devices for pixels or peripheral circuits, have been developed in order to realize high-quality and high-definition liquid crystal display devices. For example, as a technique for improving the quality of an active layer material that influences device characteristics, a technique for forming a thin film polycrystalline silicon film by using an excimer laser annealing method with an amorphous silicon film as a starting material has been developed.

In the conventional excimer laser annealing method, an energy profile of a laser beam is processed into a rectangular shape by using an optical system such as a homogenizer. And FIG.
As shown in, when laser annealing is performed on the large area substrate 10, the laser beam 11 is scanned, and at this time,
As shown in FIG. 7A, the spot shape of the laser beam 11 is processed into a square or a rectangle, and in order to make the crystal of the semiconductor thin film uniform, the overlapping portion 12 in the beam scanning direction ...
While the beam is scanned while forming the beam, in the next beam scanning, as shown in FIG. 7B, the overlapping portion 13 ... The overlapping portion 12 ... Is formed.

[0004]

However, the uniformity of the crystal is not perfect in the overlapping portion of the beam scanning, and the more the overlapping portion of the beam scanning, the more the region where the crystal uniformity is insufficient increases. Therefore, high performance of thin film transistors and the like cannot be achieved. Further, since beam scanning is repeated many times, there is a drawback that the crystallization process takes time. Further, there is a drawback that the crystal quality cannot be improved even if the profile of the laser beam is rectangular.

In view of the above circumstances, it is an object of the present invention to provide a method for producing a polycrystalline semiconductor film, which can improve the crystal quality and shorten the crystallization process time.

[0006]

In order to solve the above-mentioned problems, a method for manufacturing a polycrystalline semiconductor film according to the present invention is directed to irradiating a pulsed laser beam on an amorphous semiconductor film to melt the amorphous semiconductor film. In the method of manufacturing a polycrystalline semiconductor film by solidifying, a constant energy intensity distribution required for crystallization is provided at least in the central portion in the major axis direction, and a constant energy intensity distribution required for crystallization in the minor axis direction. Irradiating the amorphous semiconductor film with a sheet-shaped pulsed laser beam having an energy intensity distribution part and a region preceding the beam scanning direction with an energy intensity distribution part smaller than the energy required for the crystallization, and at least a short axis It is characterized in that scanning is performed at a feed pitch such that regions crystallized in the directions may overlap.

[0007]

According to the above construction, since the sheet-shaped beam is used, the overlapping portion of the beam scanning can be significantly reduced as compared with the case where the laser beam whose spot shape is square or rectangular is used. The crystal quality can be improved by suppressing an increase in the region where the uniformity is insufficient.
Further, since the pulsed laser beam has a sheet shape, the number of times of scanning can be reduced, and the time for the crystallization process can be shortened. In addition, since there is a constant energy intensity distribution portion required for crystallization in the minor axis direction and an energy intensity distribution portion smaller than the energy required for the crystallization in the region preceding the beam scanning direction, the amorphous It is possible to avoid the occurrence of a portion where the property changes abruptly between the semiconductor film and the polycrystallized semiconductor film, improve the uniformity of the crystallinity of the polycrystal semiconductor film, and further improve the crystal quality. . Alternatively, the degassing process from the amorphous semiconductor film is performed with an energy intensity lower than the crystallization energy intensity, so that peeling of the film or the like can be avoided and the crystal quality can be further improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments.

FIG. 1 is a perspective view showing an optical system of a laser irradiation apparatus for carrying out the method for producing a polycrystalline semiconductor film of the present invention, and FIG. 2 is a side view thereof. A total reflection mirror 3 is arranged on the optical path of a pulse laser beam (eg, excimer laser beam) 2 from a laser light source 1 in a direction inclined by about 45 ° with respect to the beam direction. The beam 2 reflected by the mirror 3 is incident on the beam shaping optical system 4.

The beam shaping optical system 4 comprises, for example, two double-curved cylindrical lenses, the beam 2 is processed into a sheet-like beam 2'having a predetermined width, and this is formed on a glass substrate 6 in an amorphous state. Irradiation is directed toward the silicon film 5.

As shown in FIG. 3 (a) or 3 (b), the above-mentioned sheet-like beam has a constant energy intensity distribution necessary for crystallization in the long axis direction in the entire region or in the central portion, and in the short axis direction. Has a trapezoidal distribution as shown in FIG. That is, a constant energy intensity distribution portion required for crystallization in the minor axis direction and an energy intensity distribution portion in which the energy is smaller than the energy required for the crystallization and gradually increases in the region preceding the beam scanning direction. Are formed. This trapezoidal energy intensity distribution can also be obtained by causing diffraction by shifting the beam focus position or removing a slit for obtaining a rectangular distribution.

The mirror 3 and the beam shaping optical system 4 are
It is configured to move integrally in the beam scanning direction (matching the short-axis direction and indicated by the arrow in the figure) while maintaining the mutual positional relationship, and the regions that crystallize in the short-axis direction overlap. Beam scanning is performed at a possible feed pitch.

FIG. 5 is a schematic diagram showing the state of beam scanning. For example, the width of the uniform portion (flat portion) of the beam energy in the minor axis direction is about 1 mm, the width of the portion where the energy gradually increases (inclined portion) is about 0.5 mm, n-1.
The interval between the nth beam scan and the nth beam scan is about 0.
It is set to 5 mm. Therefore, in this example, all the areas to which uniform energy (crystallization energy) is irradiated in the n-th beam scanning have already been irradiated with the portion in which the energy gradually increases in the (n-1) -th beam scanning in advance. It becomes an area. Note that this is an example, and the beam width and the scanning pitch are not limited thereto, and as another example, the beam scanning pitch may be shorter than the width of the inclined portion.

Here, the peak energy density of the laser is 200 to 500 mJ / cm ² , and the substrate temperature is room temperature to 400.
In the case where the beam scanning is performed by setting the beam width and pitch shown in FIG. 5 at 50 ° C. and the film thickness of the amorphous silicon film 5 is 50 nm, the maximum crystal grain size of the polycrystalline silicon film 5 is about 500 nm. I was able to obtain

As described above, according to the present invention, since the sheet-shaped beam 2'is used, the overlapping portion of the beam scanning is remarkably reduced as compared with the case of using the laser beam whose spot shape is square or rectangular. It is possible to suppress the increase of the region where the crystal uniformity is insufficient and improve the crystal quality. Further, since the pulsed laser beam has a sheet shape, the number of times of scanning can be reduced, and the time for the crystallization process can be shortened. In particular, by setting the width of the sheet-shaped beam 2 ′ to be slightly wider than the width of the substrate 6, the amorphous silicon film 5 on the substrate 6 can be entirely crystallized by one beam scanning.

Further, since there is a constant energy intensity distribution portion required for crystallization in the minor axis direction and an energy intensity distribution portion smaller than the energy required for the crystallization in a region preceding the beam scanning direction, Avoiding the occurrence of a portion where the property changes abruptly between the amorphous semiconductor film and the polycrystallized semiconductor film, and improving the crystallinity of the polycrystal semiconductor film to improve the crystal quality. be able to. Alternatively, the degassing treatment from the amorphous semiconductor film is performed with energy lower than the crystallization energy in the portion where the above-mentioned energy gradually increases, and film peeling or the like is avoided to further improve the crystal quality. It is possible to improve.

[0017]

As described above, according to the present invention, by scanning the sheet-like beam, it is possible to suppress the increase in the region where the crystal uniformity is insufficient and improve the crystal quality, and to reduce the number of scans. Thus, the time required for the crystallization process can be shortened. In addition, since there is an energy intensity distribution portion smaller than the energy required for crystallization in the minor axis direction, there is an effect that the crystal quality can be further improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an optical system of a laser irradiation apparatus for carrying out a method for producing a polycrystalline semiconductor film of the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is an explanatory view showing an energy profile in a long axis direction in the sheet-like beam of the present invention.

FIG. 4 is an explanatory diagram showing an energy profile in the minor axis direction of the sheet-like beam of the present invention.

FIG. 5 is a schematic view showing a state of beam scanning according to the present invention.

FIG. 6 is an explanatory view showing a method for manufacturing a polycrystalline semiconductor film by a conventional excimer laser annealing method.

FIG. 7 is an explanatory diagram showing a manner in which an overlapping portion is formed in a conventional excimer laser annealing method.

[Explanation of symbols]

 1 Laser Light Source 2 Pulse Laser Beam 2'Sheet Beam 3 Mirror 4 Beam Shaping Optical System 5 Amorphous Silicon Film 5'Polycrystalline Silicon Film

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Claims (1)

[Claims] 1. A method for producing a polycrystalline semiconductor film by irradiating an amorphous semiconductor film with a pulsed laser beam to melt and solidify the amorphous semiconductor film, which is required for crystallization in the major axis direction. Has a constant energy intensity distribution at least in the central portion, and has a constant energy intensity distribution portion required for crystallization in the minor axis direction and a region preceding the beam scanning direction is smaller than the energy required for the crystallization. The amorphous semiconductor film is irradiated with a sheet-shaped pulsed laser beam having an energy intensity distribution portion, and scanning is performed at a feed pitch such that at least regions to be crystallized in the short axis direction overlap with each other. Production method.