JPH06140323A - Method of crystallizing semiconductor film - Google Patents

Abstract

PURPOSE:To enlarge the grain size of polysiscon film. CONSTITUTION:An amorphous film 13 is inadiated with excimer laser through a diffractive optical element 14. The diffractive optical element 14 is equipped with two parallel slits 14a. The excimer laser, when passing through a slit 14a, changes into a coaxial circular wave (diffractive wave). In this case, the coaxial waves from the two slits (light sources) 14a interfere with each other, and the maximum value of the amplitude occurs periodically on the surface of the amorphous silicon film 13. Therefore, the temperature distribution of the amorphous silicon film 13 within the irradiation range of a laser diffracted light becomes one which has high-temperature range and a low temperature range. As a result, the growth speed of crystals from the nuclei of crystals existing in high-temperature range becomes larger than the growth speed of the crystals from the nuclei of crystals existing in the low temperature range, and the crystal grains having grown from the high-temperature range widens to the low-temperature range, and the grain size becomes large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor thin film crystallization method.

[0002]

2. Description of the Related Art For example, a method for manufacturing a thin film transistor by crystallizing an amorphous silicon thin film is described in FIG.
As shown in (A), a base insulating film 2 made of silicon oxide is formed on the upper surface of a glass substrate 1, an amorphous silicon thin film 3 is formed on the upper surface of the base insulating film 2, and an excimer laser is formed on the amorphous silicon thin film 3. There is a method in which the amorphous silicon thin film 3 is crystallized into a polysilicon thin film 4 by irradiating with, and the polysilicon thin film 4 is separated into elements to form a thin film transistor forming region. In this case, since the spot size of the excimer laser is as small as about several mm in diameter, the excimer laser is scanned in the x direction to irradiate the entire amorphous silicon thin film 3.

[0003]

However, in such a conventional method for crystallizing a semiconductor thin film, the amorphous silicon thin film 3 within a range of a few mm in diameter irradiated with an excimer laser is heated almost uniformly, which is why Figure 2
As shown in (B), the temperature distribution of the amorphous silicon thin film 3 within the laser irradiation range becomes substantially uniform, and as a result, crystal grains are non-selectively selected from the crystal nuclei present in the amorphous silicon thin film 3 within the laser irradiation range. Although it grows, there is a problem in that the crystal growth is saturated immediately because it is non-selective, so that the polysilicon thin film 4 having a large grain size cannot be obtained. An object of the present invention is to provide a method of crystallizing a semiconductor thin film which can increase the grain size.

[0004]

According to the present invention, a semiconductor thin film is irradiated with a laser beam through a diffractive optical element for producing a diffraction phenomenon, whereby the semiconductor thin film is crystallized.

[0005]

According to the present invention, since the semiconductor thin film is irradiated with the diffracted light of the laser, a temperature difference occurs in the semiconductor thin film within the irradiation range of the laser diffracted light, so that the semiconductor thin film exists in the high temperature region. The crystal growth rate from the crystal nuclei becomes faster than the crystal growth rate from the crystal nuclei existing in the semiconductor thin film in the low temperature region, and the crystal grains grown from the high temperature region spread to the low temperature region, thus increasing the grain size. can do.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a sectional view shown for explaining a method of crystallizing a semiconductor thin film in an embodiment of the present invention. In this semiconductor thin film crystallization method, first, a base insulating film 12 made of silicon oxide is deposited on the upper surface of a glass substrate 11 to a thickness of about 1000 Å, and then an amorphous silicon thin film 13 is formed on the upper surface to a thickness of about 500 Å. accumulate. Next, when a XeCl excimer laser having a wavelength of 308 nm is irradiated through the diffractive optical element 14 while scanning in the x direction, the amorphous silicon thin film 13 is crystallized to become a polysilicon thin film 15, as described in detail below. The diffractive optical element 14 is for generating a diffraction phenomenon, has two parallel slits 14a, and is moved in the same direction in synchronization with scanning of the excimer laser in the x direction.

Here, the crystallization of the amorphous silicon thin film 13 will be described. The excimer laser before passing through the slit 14a of the diffractive optical element 14 is a coherent plane wave and has an equiphase wavefront perpendicular to the traveling direction. When passing through the slit 14a of the diffractive optical element 14, the excimer laser causes diffraction by the Huygens' principle and changes into concentric waves (diffracted light). in this case,
Since the diffractive optical element 14 has two parallel slits 14a, concentric waves from the two slits (light sources) 14a interfere with each other, and the maximum value of the amplitude is periodically generated on the surface of the amorphous silicon thin film 13. It will happen in a timely manner. Therefore, as shown in FIG. 1B, the temperature distribution of the amorphous silicon thin film 13 in the laser diffracted light irradiation range has a high temperature region and a low temperature region.
As a result, the crystal growth rate from the crystal nuclei existing in the amorphous silicon thin film 13 in the high temperature region becomes faster than the crystal growth rate from the crystal nuclei existing in the amorphous silicon thin film 13 in the low temperature region, and the crystals grow from the high temperature region. The crystal grains will spread to the low temperature region. Therefore, the polysilicon thin film 15 having a large grain size can be obtained. The diffractive optical element 14 may have a single slit or may be a diffraction grating.

[0008]

As described above, according to the present invention, since the semiconductor thin film is irradiated with the diffracted light of the laser,
A temperature difference can be generated in the semiconductor thin film within the laser diffracted light irradiation range, so that the crystal growth rate from the crystal nuclei existing in the semiconductor thin film in the high temperature region can be increased from the crystal nuclei existing in the semiconductor thin film in the low temperature region. The crystal growth rate is higher than that of (1), the crystal grains grown from the high temperature region can be spread to the low temperature region, and thus the grain size can be increased.

[Brief description of drawings]

FIG. 1A is a sectional view for explaining a method of crystallizing a semiconductor thin film in an embodiment of the present invention, and FIG. 1B is a diagram showing a temperature distribution of an amorphous silicon thin film within a laser diffracted light irradiation range. .

2A is a cross-sectional view shown for explaining a conventional method for crystallizing a semiconductor thin film, and FIG. 2B is a view showing a temperature distribution of an amorphous silicon thin film within a laser irradiation range.

[Explanation of symbols]

 11 Glass Substrate 12 Base Insulating Film 13 Amorphous Silicon Thin Film 14 Diffractive Optical Element 14a Slit 15 Polysilicon Thin Film

Claims (2)

[Claims] 1. A method for crystallizing a semiconductor thin film, which comprises irradiating a semiconductor thin film with a laser through a diffractive optical element for producing a diffraction phenomenon, thereby crystallizing the semiconductor thin film. 2. The method of crystallizing a semiconductor thin film according to claim 1, wherein the diffractive optical element has one or more pairs of parallel slits.