JPH11330000A - Laser annealing method for non-single crystal thin film - Google Patents

Abstract

(57) [Problem] It is difficult to improve the uniformity and the yield of an element manufactured using this crystallized thin film because the crystallinity of the crystallized thin film is caused by the intensity unevenness of the pulsed laser beam. there were. A method of crystallizing a non-single-crystal thin film on a substrate by scanning a pulse laser beam and irradiating the non-single-crystal thin film with the pulse laser beam, wherein an angle between a major axis direction of the pulse laser beam and the scanning direction is formed. Irradiation is performed at α of 5 to 85 ° to crystallize.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film transistor, an image sensor, and an SRAM for a liquid crystal display device.
And the like.

[0002]

2. Description of the Related Art In recent years, demands for larger and higher definition liquid crystal display devices have been increasing due to demands for monitors of notebook computers and video cameras. In response to this demand, liquid crystal display devices using a low-temperature polysilicon thin film transistor array have been in full swing for mass production due to recent advances in manufacturing technology.

In order to form a polysilicon layer used in a low-temperature polysilicon thin film transistor array, a method of annealing an amorphous Si thin film by excimer laser irradiation (hereinafter referred to as excimer laser annealing) is generally used.

FIGS. 5 to 7 show a conventional laser annealing method. In this conventional laser annealing method, a pulsed laser beam 1 is applied to an amorphous Si thin film 2 on a substrate 4.
Irradiation is performed to form a polycrystalline Si thin film 3 in the irradiated area.
Subsequently, irradiation is performed by scanning the pulse laser beam 1b in the direction of arrow B so as to overlap the irradiation region of the pulse laser beam 1a. By repeating the same process, a polycrystalline Si thin film is formed on the entire surface of the substrate without gaps.

Here, the major axis diameter of the pulse laser beams 1a and 1b is 200 mm, the minor axis diameter is 400 μm, the average beam intensity is 300 mJ / cm ² , and the beam superimposing irradiation direction is 90 degrees with respect to the beam major axis direction. 20 μm in the direction of the eggplant
Irradiation is performed at a pitch.

In general, a line-shaped laser beam can be crystallized on the entire surface of the substrate by superimposing irradiation in only one axial direction, and thus is often used mainly from the viewpoint of shortening the laser annealing process time.

[0007]

FIG. 7 shows an example of the irradiation intensity history for each pulsed laser beam on the fixed point AA 'line in the plane of the substrate 4 shown in FIG.

In the performance of the current forming optical system of a linear laser beam, intensity irregularities with a peak-to-peak value width of several percent exist on the major axis of the beam, and form 90 degrees with respect to the major axis direction of the beam. Since the beams are superimposed in the directions, the beam portions having the same intensity are superimposed.

As can be seen from FIG. 7, in a region where a low intensity portion on the beam long axis is irradiated first, only a portion where the intensity is low is thereafter superimposed, and similarly, a portion where the initial intensity is high is also thereafter. Only the part with the high intensity is irradiated with the superposition.

Therefore, since the crystallization rate of the polycrystalline Si thin film formed by laser annealing depends on the beam intensity, the portion where the beam intensity non-uniformity overlaps causes linear crystallization non-uniformity.

According to the experiments of the present inventors, when a thin film transistor array was manufactured using a polycrystalline Si thin film formed by a conventional laser annealing method, linear characteristics in a direction parallel to a beam scanning axis were defective or poor. Several inferior transistor groups were found.

Accordingly, an object of the present invention is to reduce crystallization unevenness while using a current pulsed laser beam, and to improve the yield of devices manufactured using the crystallized thin film.

[0013]

The present invention is characterized in that the substrate is irradiated with the laser beam inclined in the major axis direction with respect to the scanning direction of the pulse laser beam.

According to this invention, even in a region irradiated by one shot at an intensity largely deviated from the average beam intensity, the irradiation position of the pulsed laser beam is shifted in the major axis direction with respect to the substrate. Since shots are most frequently superimposed and illuminated near the average beam intensity,
The average crystallization rate substantially converges in the substrate plane, and the crystallization unevenness is reduced, so that the yield of an element manufactured using this crystallized film can be improved.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The laser annealing method for a non-single-crystal thin film according to the present invention is characterized in that the non-single-crystal thin film on a substrate is scanned and irradiated with a pulsed laser beam for crystallization. It is characterized in that irradiation is performed with the major axis direction inclined with respect to the scanning direction.

More specifically, the irradiation is performed at an angle between the long axis direction of the pulsed laser beam and the scanning direction thereof of 5 to 85 degrees. When the ratio between the major axis diameter and the minor axis diameter of the pulsed laser beam is 100 or more, the scanning pitch for each pulsed laser beam irradiation is d, and the angle is α, d · cosα is 2
μm or more. The spatial average intensity of the pulse laser beam is 200 to 400 mJ / cm ² .

Hereinafter, a laser annealing method for a non-single-crystal thin film of the present invention will be described based on specific embodiments. (Embodiment) FIGS. 1 to 4 show an embodiment of the present invention.

As shown in FIG. 1, when the non-single-crystal thin film 2 on the surface of the substrate 4 is scanned and irradiated with the pulse laser beam 1 to crystallize, the pulse laser beam 1 is scanned in the major axis direction L. Irradiation was carried out at an angle to the direction B. Specifically, the polycrystalline Si thin film 3 was formed by performing overlapping irradiation while setting the angle α between the major axis direction L and the scanning direction B of the pulse laser beam 1 to 45 degrees.

Here, the minor axis diameter of the beam is 400 μm, the major axis diameter is 200 mm, and the average beam intensity is 300 mJ / cm.
² , and there is a maximum of ± 10% strength unevenness at intervals of about 1 mm. The beam scanning pitch d for each shot is 20 μm.
m.

FIG. 2 shows an example of the irradiation intensity history for each pulsed laser beam on the fixed point AA 'line in the plane of the substrate 4 shown in FIG.
Shown in As can be seen from a comparison between FIG. 2 and FIG. 7 showing the conventional example, this embodiment is different from the conventional example, and as shown in FIG.
Superimposed irradiation is performed while shifting in the long axis direction by 4.1 μm. Here, if d · cos α is 2 μm or more, the same effect can be obtained.

FIGS. 3 and 4 show that the amorphous Si thin film 2 on the substrate 4 is subjected to a plurality of shots with a beam intensity of 300 mJ / cm ² and a certain number of 270 mJ / cm ² or 33 mJ / cm ^2.
The crystallization rate of a region irradiated with spots in which shots of 0 mJ / cm 2 are mixed is shown.

As can be seen from FIGS. 3 and 4, even when a small number of shots having different intensities coexist in addition to the multiple shots, if shots (superimposed irradiation) are superposed at the same intensity, the shot intensity remains constant. the field crystallization rate tends to be saturated to a constant value C ₀ in. Here, if the intensity of the multiple shots is in the range of 200 to 400 mJ / cm ² , the same effect can be obtained.

Therefore, according to the laser annealing method of the present invention, even in the irradiation area where the minimum is 270 mJ / cm ² or the maximum is 330 mJ / cm ² in the first beam, the beam intensity is 300 mJ / c after the next shot.
Since superimposed irradiation is performed in the vicinity of m ² , the crystallization rate of the irradiated area is substantially converged to C ₀ .

In the above embodiment, the angle α = 45 °. However, compared to the conventional method of α = 90 °, the angle α = 45 °.
Good results were obtained in the range of 5 degrees. In the above embodiment, the short axis diameter of the beam is 400 μm and the long axis diameter is 200 mm.
However, similar results were obtained when the ratio of the major axis diameter to the minor axis diameter of the beam was 100 or more.

[0025]

As described above, according to the present invention, the crystallization unevenness of a polycrystalline thin film to be easily formed can be reduced while using the current pulse laser beam. This is effective for improving the yield of devices manufactured using the method.

[Brief description of the drawings]

FIG. 1 is a plan view showing an irradiation state of laser annealing in a laser annealing method for a non-single-crystal thin film of the present invention.

FIG. 2 is an explanatory diagram of a laser beam irradiation history at a fixed point AA ′ of the embodiment.

FIG. 3 is a diagram showing a measurement result of a ratio of irradiating the pulse laser beam of the embodiment with a plurality of shots of the same intensity mixed with shots of different intensities and a crystallization ratio.

FIG. 4 shows amorphous S by pulsed laser beam superimposed irradiation.
Schematic diagram illustrating the laser annealing process of the i-thin film

FIG. 5 is a perspective view of a conventional laser beam irradiation state.

FIG. 6 is a plan view of the conventional example.

FIG. 7 is an explanatory diagram of a laser beam irradiation history at a fixed point AA ′ in the conventional example.

[Explanation of symbols]

 Reference Signs List 1 pulse laser beam 1a irradiation pulse laser beam 1b next irradiation pulse laser beam 2 amorphous Si thin film 3 polycrystalline Si thin film 4 substrate

Claims (5)

[Claims] 1. A method for irradiating a non-single-crystal thin film on a substrate by scanning a pulsed laser beam and irradiating the non-single-crystal thin film with a pulsed laser beam inclined in a major axis direction with respect to the scanning direction. Laser annealing method for single crystal thin film. 2. The laser annealing method for a non-single-crystal thin film according to claim 1, wherein the irradiation is performed by setting the angle between the major axis direction of the pulse laser beam and its scanning direction to 5 to 85 degrees. 3. The pulse laser beam according to claim 1, wherein a ratio of a major axis diameter to a minor axis diameter is 100 or more.
A method for laser annealing a non-single-crystal thin film according to claim 2. 4. The non-single-crystal thin film laser according to claim 3, wherein d · cos α is 2 μm or more, where d is a scanning pitch for each irradiation of the pulsed laser beam and α is the angle. Annealing method. 5. The laser annealing method for a non-single-crystal thin film according to claim 4, wherein the pulse laser beam has a spatial average intensity of 200 to 400 mJ / cm ² .