JPH1167663A - Method for manufacturing semiconductor device - Google Patents

Abstract

[PROBLEMS] To improve the characteristics of a thin film transistor by stably forming a polysilicon film having a large crystal grain size of an amorphous silicon film. SOLUTION: A silicon thin film and a thickness of 10 to 300 mm on a substrate.
With the silicon oxide film (preferably 10 to 100 °) formed, the silicon thin film is irradiated with a laser beam to crystallize the silicon thin 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 semiconductor device, and more particularly to crystallization of a semiconductor thin film in manufacturing a semiconductor device such as a thin film transistor.

[0002]

2. Description of the Related Art XeCl on amorphous silicon (a-Si) thin film
A conventional example in which a polysilicon thin film is formed by irradiating an excimer laser will be described below.

FIG. 3 is an explanatory view of a conventional example of a crystallization step. In FIG. 3A, a silicon oxide (SiO ₂ ) film 2 having a thickness of 2000 mm is formed on a glass substrate 3 using a plasma-enhanced chemical vapor deposition (PCVD) apparatus to prevent contamination from the substrate. 500-mm-thick hydrogenated amorphous silicon film (a-Si:
H) Form 1.

In FIG. 3B, the substrate is heated to a temperature of 450 ° C.
Thermal annealing is performed in a nitrogen atmosphere for 1 hour. Thereby, ablation due to bumping of hydrogen during laser irradiation can be prevented, and the amorphous silicon film 4 is formed. Natural oxide film on the surface of amorphous silicon film 5
Has occurred.

In FIG. 3C, during the laser irradiation process, the natural oxide film 5 on the surface of the amorphous silicon is usually removed by immersing the substrate in a hydrofluoric acid solution or the like.

In FIG. 3D, the pressure is 1 × 10 ⁻⁵ Torr.
Irradiate the laser beam 6 in a vacuum or nitrogen atmosphere and scan in the direction of the arrow. In FIG. 3E, the amorphous silicon film 1 is crystallized to obtain a polysilicon film 7.

FIG. 4 is an explanatory diagram of another conventional example. In this example, a 500-nm-thick silicon oxide film is formed as an antireflection film 8 on the surface of the amorphous silicon film 1 for the purpose of efficiently using laser energy and flattening the film surface.

[0008]

FIG. 5 is a diagram showing the dependence of the crystal grain size on the laser energy with respect to the conventional example. In the figure, the crystal grain size increases as the laser energy increases, and in this case, the maximum value is reached at 400 mJ / cm ² .

When laser annealing is performed after removing the natural oxide film on the surface, only small crystal grains of about 0.2 μm can be formed, and when an antireflection film is formed, the laser energy is 400 mJ / cm. ² , relatively large crystal grains of 0.5 μm can be obtained.However, if the irradiation energy slightly exceeds the optimum value due to fluctuations in the energy of the laser device itself, the film will ablate, and semiconductor elements such as thin film transistors can be formed. Will be gone.

An object of the present invention is to improve the characteristics of a thin film transistor by stably forming a polysilicon film having a large crystal grain size.

[0011]

Means for solving the above problems are as follows: 1) A silicon thin film and a silicon oxide film having a thickness of 10 to 300 mm are sequentially formed on a substrate, and the silicon thin film is irradiated with laser light to form the silicon thin film. A method for manufacturing a semiconductor device for crystallization of a silicon thin film, or 2) a method for manufacturing a semiconductor device according to 1 above, wherein the silicon oxide film is formed by plasma vapor deposition, or 3) a method for manufacturing the silicon oxide film, 4. The method of manufacturing a semiconductor device according to the above 1, wherein the method is performed by sputtering, or 4) the method of manufacturing a semiconductor device according to the above 1, wherein the silicon oxide film is formed by heating the film in an atmosphere containing oxygen atoms. 5) The method of manufacturing a semiconductor device according to 1 above, wherein the silicon oxide film is formed by irradiating the silicon oxide film with ultraviolet light in an atmosphere in which oxygen atoms are present. After the silicon oxide film formed is achieved by the method of manufacturing a semiconductor device of the 1, wherein patterning the silicon oxide film into a desired shape.

The present invention utilizes the result of experimentally confirming the appropriate thickness of a silicon oxide film on an amorphous silicon film. The inventor has experimentally confirmed the range of the film thickness at which the crystal grain size is maximized and ablation does not occur even when the laser energy exceeds the maximum value.

[0013]

FIG. 2 is an explanatory diagram of an embodiment of the present invention. In FIG. 2 (A), a silicon oxide (SiO ₂ ) film 2 having a thickness of 2000 mm is formed on a glass substrate 3 using a plasma vapor deposition apparatus to prevent contamination from the substrate. A hydrogenated amorphous silicon film 1 and a silicon oxide film 9 having a thickness of 100 mm are continuously grown.

In FIG. 2 (B), the substrate is heated to 450 ° C.
By performing thermal annealing in a nitrogen atmosphere for one hour, the hydrogenated amorphous silicon is dehydrogenated to form an amorphous silicon film 4.

In FIG. 2C, a laser beam 6 is irradiated in a vacuum of about 1 × 10 ⁻⁵ Torr or in a nitrogen atmosphere to scan in the direction of the arrow. In FIG. 2D, the amorphous silicon film 1 is crystallized to obtain a polysilicon film 7.

FIG. 1 is a diagram illustrating the principle of the present invention. The figure is
The dependence of the crystal grain size on the laser energy when a silicon oxide film having a thickness of 100 ° is formed on the surface of the amorphous silicon film is shown.

At a laser energy of 400 mJ / cm ² , large crystal grains with a grain size of about 1 μm are obtained. Even when the laser energy exceeds 400 mJ / cm ² , the crystal grain size is reduced, but the thickness is reduced. It can be seen that the ablation of the amorphous silicon film as occurred when using the 500-mm anti-reflection film has not occurred.

As a result, it is possible to prevent a catastrophic damage such that a thin film transistor cannot be formed even when energy exceeding the optimum value is irradiated due to fluctuations in the energy of the laser device.

According to the experimental results of the inventors, compared with the case where the natural oxide film on the amorphous silicon film is removed,
The thickness of the silicon oxide film is 10-300 mm so that larger crystal grains can be obtained and ablation does not occur when an anti-reflection film with a thickness of 500 mm is formed.
It has been found to be preferably between 10 and 100 °.

In the embodiment, the silicon oxide film on the amorphous silicon is formed by plasma vapor deposition. However, the present invention is not limited to this. For example, the silicon oxide film may be formed by sputtering, heating in an atmosphere of oxygen atoms, or It may be formed by a method of irradiating ultraviolet light in an atmosphere of oxygen atoms.

In the embodiment, the silicon oxide film on the amorphous silicon is formed uniformly over the entire surface of the substrate. However, the present invention is not limited to this. The silicon oxide film is formed only on a desired region by photolithography. Then, a polysilicon film having a large crystal grain size may be formed only in that region.

Next, data showing the basis for limiting the numerical value of the oxide film thickness will be described with reference to Table 1.

[0023]

[Table 1] Table 1 shows the crystal grain size (μm) formed when the laser energy is 400 mJ / cm ² and 500 mJ / cm ² .

In the case of 500 mJ / cm ² , the oxide film thickness is 400Å
Above is inappropriate because it causes ablation. In the case of 400 mJ / cm ² , the crystal grain size is large when the oxide film thickness is 10 mm or more.

Therefore, the reason why the crystal grain size is large at 400 mJ / cm ² and that ablation does not occur at 500 mJ / cm ² is that the oxide film thickness is 10 to 300 mm, of which the crystal grain size is particularly large. It turns out that it is 10-100 mm.

[0026]

According to the present invention, it is possible to form larger crystal grains as compared with the case where the oxide film on the surface of the amorphous silicon film is removed. Ablation of the amorphous silicon film, which has occurred when the energy exceeds the optimum value, can be avoided.

As a result, a polysilicon film having a large crystal grain size can be formed stably, and the characteristics of a thin film transistor formed of the polysilicon film using the polysilicon film can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of the present invention (a diagram showing laser energy dependence of the present invention).

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

FIG. 3 is an explanatory view of Conventional Example 1.

FIG. 4 is an explanatory view of a second conventional example.

FIG. 5 is a diagram showing the dependence of the crystal grain size on the laser energy in the conventional example.

[Explanation of symbols]

1 hydrogenated amorphous silicon (a-Si: H) 2 silicon oxide (SiO ₂ ) film 3 glass substrate 4 amorphous silicon (a-Si) 5 native oxide SiO ₂ film 6 laser beam 7 polysilicon film 8 anti-reflection film With SiO ₂ film 9 Silicon oxide (SiO ₂ ) film

Claims (6)

[Claims] 1. A silicon thin film and a thickness of 10 to 300 mm on a substrate.
And irradiating the silicon thin film with a laser beam in a state where the silicon oxide film is formed in order, thereby crystallizing the silicon thin film. 2. The method for manufacturing a semiconductor device according to claim 1, wherein said silicon oxide film is formed by plasma vapor deposition. 3. The method according to claim 1, wherein the silicon oxide film is formed by a sputtering method. 4. The method for manufacturing a semiconductor device according to claim 1, wherein said silicon oxide film is formed by heating in an atmosphere in which oxygen atoms are present. 5. The method for manufacturing a semiconductor device according to claim 1, wherein the silicon oxide film is formed by irradiating ultraviolet light in an atmosphere containing oxygen atoms. 6. The method according to claim 1, wherein after forming the silicon oxide film, the silicon oxide film is patterned into a desired shape.