JPH06140321A - Method of crystallizing of semiconductor film - Google Patents

Abstract

PURPOSE:To enlarge the grain size of a polysilicon film. CONSTITUTION:An amorphous silicon film 13 is crystallized and made a polysilicon film 16 by providing a buffer insulating film 14 consisting of silicon oxide and a laser reflecting film consisting of chromium, in stripe shape or in mosaic shape, on the topside of an amorphous silicon film 13, and applying excimer laser. In this case, the laser reflecting film 15 reflects an excimer laser, so the amorphous silicon film 13 in the section where the temperature of a laser reflecting film 15 does not exist within the application range of an excimer laser becomes high, but the temperature of the amorphous silicon film 13 in the section where the laser reflecting film 15 exists becomes low. 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 laser reflection film is provided on a semiconductor thin film in a stripe shape or a mosaic shape, and the semiconductor thin film is crystallized by irradiating a laser in this state. Is.

[0005]

According to the present invention, a part of the irradiated excimer laser is reflected by the laser reflection film, so that the semiconductor thin film becomes high in temperature in the part where the laser reflection film does not exist within the irradiation range of the excimer laser. The temperature of the semiconductor thin film in the portion where the laser reflection film is present becomes low, so that the crystal growth rate from the crystal nuclei existing in the semiconductor thin film in the high temperature region is the crystal growth rate from the crystal nuclei existing in the semiconductor thin film in the low temperature region. As a result, the crystal grains grown from the high temperature region spread to the low temperature region, so that the grain size can be increased.

[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, a buffer insulating film 14 made of silicon oxide is deposited on the entire upper surface of the amorphous silicon thin film 13 to a thickness of several hundred Å, and then a laser reflection film 15 made of chromium is deposited on the upper surface to a thickness of about 1000 Å. Then, these are patterned by a well-known photolithography in a stripe shape or a mosaic shape with a pitch of several μm in both width and interval. Next, when a XeCl excimer laser having a wavelength of 308 nm is scanned and irradiated in the x direction, the amorphous silicon thin film 13 is crystallized to become a polysilicon thin film 16, as described in detail below. After that, the laser reflection film 15 and the buffer insulating film 14 are removed.

Here, the crystallization of the amorphous silicon thin film 13 will be described. When the excimer laser is irradiated, the laser reflection film 15 reflects the excimer laser. Therefore, the amorphous silicon thin film 13 in the portion where the laser reflection film 15 exists is not irradiated with the excimer laser and the portion where the laser reflection film 15 does not exist. The amorphous silicon thin film 13 is irradiated with the excimer laser. Moreover, since the width and interval of the laser reflection film 15 are both several μm, which is considerably smaller than the spot size (diameter of several mm) of the excimer laser, the laser reflection film is within the irradiation range of one excimer laser. The amorphous silicon thin film 13 in the portion where the laser reflection film 15 does not exist has a high temperature, whereas the amorphous silicon thin film 13 in the portion where the laser reflection film 15 exists has a low temperature. Therefore, as shown in FIG. 1B, the temperature distribution of the amorphous silicon thin film 13 in the laser irradiation range is a temperature distribution in which high temperature and low temperature are alternately repeated. As a result, the crystal growth rate from the crystal nuclei existing in the amorphous silicon thin film 13 in the high temperature region, that is, the portion where the laser reflection film 15 does not exist is present in the amorphous silicon thin film 13 in the low temperature region, that is, the portion where the laser reflection film 15 exists. The crystal growth rate from the crystal nuclei becomes higher, and the crystal grains grown from the high temperature region spread to the low temperature region. Therefore, the polysilicon thin film 16 having a large grain size can be obtained.

[0008]

As described above, according to the present invention, the semiconductor thin film in the portion where the laser reflecting film does not exist within the irradiation range of the excimer laser is heated to a high temperature, and the semiconductor thin film in the portion where the laser reflecting film exists falls to a low temperature. Therefore, the crystal growth rate from the crystal nuclei present in the semiconductor thin film in the high temperature region becomes faster than the crystal growth rate from the crystal nuclei present in the semiconductor thin film in the low temperature region,
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 according to 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 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 Buffer Insulating Film 15 Laser Reflecting Film 16 Polysilicon Thin Film

Claims (2)

[Claims] 1. A method of crystallizing a semiconductor thin film, comprising providing a laser reflecting film in a stripe shape or a mosaic shape on a semiconductor thin film, and irradiating a laser in this state to crystallize the semiconductor thin film. 2. A buffer insulating film is provided between the semiconductor thin film and the laser reflecting film.
A method for crystallizing a semiconductor thin film as described above.