JPH10199808A - Method of crystallizing silicon film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly and isotropically crystallize an amorphous Si film by shaping a laser beam having an axial length sufficiently covering the long side of an Si film region and scanning this beam in a specified direction and then orthogonal direction thereto over the Si film. SOLUTION: A laser pulse is shaped in a beam L of about 0.5mm wide and length exceeding the long side of a glass substrate 1. An amorphous Si film 6 at panel regions 7a-7d is scanned by this beam L in the long-side direction of the substrate 1 and then in the orthogonal direction to the long side of the substrate 1, to thereby crystallize the Si film 6 isotropically and uniformly in one direction and orthogonal direction thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for crystallizing a silicon film of a thin film transistor used as a switch element of a liquid crystal display, and more particularly to a method for achieving uniform and isotropic crystallization.

[0002]

2. Description of the Related Art Among active matrix liquid crystal displays (LCDs), those using thin film transistors (TFTs) as switching elements have excellent image quality. ) Are also being manufactured in large numbers.

[0003] Large-screen LCDs are required to have high image uniformity and high mobility of TFTs. In order to achieve high mobility, a polysilicon (polycrystalline silicon) type TFT capable of increasing the charge mobility according to the crystal grain size is used as compared with an amorphous silicon type TFT having a relatively small charge mobility. Is preferred.

Further, an amorphous silicon type TFT (a
-SiTFT), it is very difficult to integrate peripheral circuits on the same substrate. Therefore, a peripheral circuit is formed on another substrate and connected to the pixel portion. As a result, the manufacturing process becomes complicated, and there is a limit to miniaturization of pixels (and thus to increase in number of pixels).
On the other hand, polysilicon type TFT (p-Si TFT)
In this case, the pixel portion and the peripheral circuit portion can be formed monolithically on the same substrate. From these points, as a switching element, expectation is particularly focused on a polysilicon TFT.

When using a polysilicon type TFT,
After forming an amorphous silicon (a-Si) film on a substrate, it is effective to crystallize the a-Si film.
This crystallization method includes a solid phase crystallization method and a laser anneal method. However, the solid-phase crystallization method requires about 600
Annealing is performed in a high temperature atmosphere of
In the case of a CD, there is a possibility that the glass substrate is deformed, so that a lower temperature is required. On the other hand, laser annealing can be performed in a low-temperature reaction chamber where the glass substrate is not melted.

Among the methods for crystallizing an a-Si film by laser annealing, one of the methods that has been actively studied in recent years is to form an excimer laser optically into a linear (or rectangular) beam, and to apply the line to the beam. This is a method of scanning the a-Si film by a beam at a predetermined overlap ratio.

In this conventional line beam scanning method,
The length of the beam in the longitudinal direction on a plane perpendicular to the optical axis is fixed, and scanning is performed only in one of the vertical and horizontal directions of the glass substrate.

[0008]

However, with the increase in the screen size of the LCD as described above, glass substrates having a large area are increasing. In addition, in the process of forming pixels and peripheral circuits, from the viewpoint of manufacturing cost reduction, it is general to provide a plurality of panel regions on one wide glass substrate and form pixels and peripheral circuits in those regions in parallel. Is being done. As a result, in the conventional line beam scanning method,
The length in the longitudinal direction of the beam was considerably shorter than the length of the long side of the glass substrate or panel region, and in many cases, only one portion of the glass substrate or panel region could be covered by a single scan.

In such a case, as shown in FIG. 4, after a part of the glass substrate (or panel area) 10 is scanned by the line beam L, the scan start position is set to scan the remaining part. I had to repeat the process of performing a line feed operation to reset the settings, and then restarting the scan several times. Performing the scan several times by dividing into several parts as described above has the following inconveniences. (1) The crystal density of the a-Si film becomes non-uniform due to, for example, the inconsistent energy densities of the line beams at the time of each scan, which may lead to deterioration of the image quality of the LCD. is there. (2) As the number of scans increases, the throughput of the crystallization process decreases.

When the a-Si film is scanned by a laser, crystallization of the a-Si film is promoted in the scanning direction. Therefore, the conventional line beam scanning method has the following disadvantages. (3) When there is an optical defect in a direction orthogonal to the scanning direction, the optical defect may remain as a linear defect, which may also lead to a decrease in the image quality of the LCD. (4) Since the characteristics of the TFT change between the case where the channel of the TFT is formed along the scanning direction and the case where the channel is formed along the direction orthogonal thereto, the degree of freedom in the layout of the TFT is restricted. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and aims to provide a method capable of uniformly and isotropically crystallizing an a-Si film and preventing a decrease in crystallization processing throughput. is there.

[0012]

According to a method of crystallizing a silicon film according to the present invention, a step of shaping a laser into a beam whose longitudinal length is equal to or longer than the length of a long side of a region where the silicon film exists is provided. Scanning the silicon film in a predetermined direction with the beam, and scanning the silicon film in a direction substantially orthogonal to the predetermined direction with the beam.

According to this crystallization method, the silicon film is scanned with a beam whose length in the longitudinal direction is equal to or longer than the length of the long side of the silicon film region. Is irradiated. Therefore, the silicon film can be uniformly crystallized with a laser having a uniform energy density.

Further, since scanning is performed in both directions of a predetermined direction and a direction substantially perpendicular thereto, the silicon film is isotropically crystallized not only in one direction but also in a direction substantially perpendicular thereto. Therefore, optical defects hardly remain, and the TFT characteristics do not change regardless of the direction in which the channel of the TFT is formed, thereby increasing the degree of freedom in layout. Also, since the number of scans is only two, there is no reduction in throughput.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an example of a glass substrate. The glass substrate 1 has a rectangular shape with a long side of about 450 mm and a short side of about 350 mm.
Four rectangular panel areas 7a to 7d having a length of 00 mm and a short side of about 150 mm (10 inch type) are provided (that is, four panels are provided).

In each of the panel areas 7a to 7d, for example, FIG.
As shown in FIG. ₂ , an SiO ₂ film 2 is formed on a glass substrate 1 to prevent contamination of a gate electrode by impurities, and a metal such as Cr (chromium) or Mo (molybdenum) is patterned thereon. Thereby, the gate electrode 3 is formed. A gate insulating film (for example, about 100 nm thick) is formed on the gate electrode 3 by a plasma CVD method.
And a SiO ₂ film 5) having a thickness of about 50 nm. And on these gate insulating films,
Approximately 50 film thickness by plasma CVD or low pressure CVD
A nm-a-Si film 6 is deposited.

In order to crystallize the a-Si film 6, a laser pulse of a predetermined frequency (for example, frequency 200 Hz) generated from an excimer laser oscillator (not shown) is irradiated with an energy density using an optical system (not shown). Is shaped into a uniform (for example, less than 5% variation) linear (or rectangular) beam of, for example, 360 mJ / cm ² , and the glass substrate 1 is moved at a constant speed relative to the line beam. Thus, scanning is performed at a predetermined overlap rate (for example, 95%).

Therefore, in the present invention, first, a laser pulse generated from an excimer laser oscillator is set to a length (longitudinal length) of 450 mm or more and a width of 0 mm based on 450 mm which is the length of the long side of the glass substrate 1. The beam is shaped into a 0.5 mm beam (however, the horizontal length may be other than 0.5 mm).

As shown in FIG. 3A, the beam L is applied to each of the panel regions 7a to 7a in the long side direction of the glass substrate 1.
The d-a-Si film 6 is scanned. As a result, the entire a-Si film 6 is irradiated with a laser, so that each a-S
The i film 6 is uniformly crystallized.

Subsequently, as shown in FIG. 3B, the beam L scans the a-Si film 6 in each of the panel regions 7a to 7d in a direction orthogonal to the long side of the glass substrate 1. Also at this time, since the entire a-Si film 6 is irradiated with the laser, each a-Si film 6 is uniformly crystallized. Further, since the scanning is performed in both directions of the long side direction of the glass substrate 1 and the direction orthogonal thereto, a-Si
The film 6 is isotropically crystallized not only in one direction but also in a direction orthogonal thereto. Conversely, after scanning in the direction perpendicular to the long side of the glass substrate 1 as shown in FIG. 3B, scanning may be performed in the long side direction of the glass substrate 1 as shown in FIG. 3A.

When the crystallization of the a-Si film 6 is completed as described above, well-known steps for forming pixels and peripheral circuits (patterning of the a-Si film 6, formation of a source and a drain, formation of an interlayer insulating film, etc.) Formation, formation of contact holes, wiring with signal lines and gate lines, formation of transparent electrodes, etc.) and subsequent well-known steps (such as lamination of substrates, injection of liquid crystal, and division of panels).

As described above, according to this crystallization method, the a-Si film is uniformly crystallized by the laser having a uniform energy density, and the a-Si film is formed not only in one direction but also in a direction orthogonal thereto. Is also crystallized isotropically. Also,
Since the number of scans is only two, the throughput of the crystallization process does not decrease. The laser pulse generated from the excimer laser oscillator was applied to the glass substrate 1
Instead of using the long side length of 450 mm as a reference,
200 mm which is the length of the long side of each of the panel regions 7a to 7d
The beam may be shaped into a beam having a length (length in the longitudinal direction) of 200 mm or more based on.

In the above embodiment, the present invention is applied to a process of manufacturing an LCD having a bottom gate polysilicon TFT. However, the present invention is applied to a process of manufacturing an LCD having a top gate polysilicon TFT. Of course, the invention may be applied.

The conditions such as the frequency of the excimer laser and the overlap ratio of the scan are not limited to those described in the above embodiments, but may be any suitable ones. In the above embodiments, the present invention is applied to a case where line beam scanning is performed using an excimer laser. However, the present invention may be applied to a case where a laser other than an excimer laser is used.

In the above embodiments, a polysilicon type TFT used as a switching element of a liquid crystal display is used.
Although the present invention is applied to crystallize a silicon film of the present invention, the present invention may be applied to crystallize other silicon films. In addition, the present invention is not limited to the above-described embodiments, and may take various other configurations without departing from the gist of the present invention.

[0026]

As described above, according to the present invention, it is possible to uniformly and isotropically crystallize a silicon film such as a polysilicon type TFT used as a switching element of a liquid crystal display. There is an effect that a decrease in throughput can be prevented. Therefore, in particular, if the present invention is applied in the process of manufacturing a large-screen liquid crystal display, it is possible to efficiently manufacture a liquid crystal display having a uniform image.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a glass substrate on which an a-Si film is deposited.

FIG. 2 is a cross-sectional view of the glass substrate of FIG.

FIG. 3 is a plan view showing an embodiment of the present invention.

FIG. 4 is a diagram showing an example of a laser scanning process in a conventional crystallization process.

[Explanation of symbols]

1 glass substrate, 6a-Si film, 7a-7d panel area

Claims (2)

[Claims] 1. A method for crystallizing a silicon film, wherein the silicon film is crystallized by laser annealing, wherein the laser is shaped into a beam whose length in the longitudinal direction is longer than the length of the long side of the region where the silicon film exists. Scanning the silicon film in a predetermined direction with the beam; and scanning the silicon film in a direction substantially orthogonal to the predetermined direction with the beam. How to crystallize the film. 2. A method for crystallizing a silicon film on a substrate of a liquid crystal display by laser annealing, the method comprising: irradiating a laser beam having a longitudinal length equal to or longer than a long side of the substrate. Or a beam whose length in the longitudinal direction is equal to or longer than the length of the long side of the area of the liquid crystal display panel on the substrate; and Scanning the silicon film in one of a direction substantially parallel to the direction and a direction substantially perpendicular to the long side, and by the beam, the direction substantially parallel to the long side of the substrate and the long side. Scanning the silicon film in the remaining one of the directions substantially orthogonal to each other.