JPH1145856A - Film-forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase crystal particles by low energy laser beam by a method, wherein a crystallization promoting silicon oxide film is formed on a glass substrate, and a silicon film formed thereon by a chemical vapor phase growth is heated. SOLUTION: A crystallization promoting silicon oxide film 12 is formed on a quartz substrate 11 by a plasma chemical vapor deposition(CVD) method using gas containing silicon and O2 . Next, an amorphous silicon film 13 is formed on the crystallization promoting silicon oxide film 12 by the plasma CVD method using SiH4 gas. At the time of irradiating next laser beam, hydrogen in the silicon film 13 is expanded and ejected out through rapid heating, and a hole is opened in the silicon film 13. Therefore, hydrogen is removed from the silicon film 13 by heating at a temperature of about 450 deg.C. By irradiating laser beams to the amorphous silicon film 13, silicon recrystallizes and a polysilicon film 13a composed of silicon crystal particles having a particle size of about 100 mm or more is obtained, and since the energy of laser beams is low, a surface roughness such as a projection does not occur on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a film forming method, and more particularly, to a film forming method for forming a polysilicon film on a glass substrate. In recent years, as applications to liquid crystal display devices (LCD), solar cells, and the like, a polysilicon film is often formed on a glass substrate and used. In this case, an element such as a transistor is formed on the polysilicon film, and it is desired to improve the mobility of carriers in the polysilicon film in order to improve the element characteristics.

[0002]

2. Description of the Related Art A conventional method for forming a polysilicon film on a glass substrate will be described with reference to FIG. For the formation of a silicon film on a glass substrate, a plasma CVD method that can easily handle a large glass substrate is used.

[0003] First, as shown in FIG. ₄ (a), SiH 4
A silicon film 2 is formed on a glass substrate 1 by a plasma CVD method using a gas. In this case, the silicon film 2 becomes amorphous. Next, as shown in FIG. 4B, hydrogen is removed from the silicon film 2 by heating at 450 ° C.

Next, as shown in FIG. 4C, the amorphous silicon film 2 is irradiated with laser light. At this time, the energy of laser light is considerably increased in order to increase the crystal grain size. Usually, the energy is 350 mJ / cm ² or more. The irradiation of the laser beam heats the amorphous silicon and recrystallizes the silicon to increase the crystal grain size of the silicon crystal, thereby obtaining a polycrystalline silicon film 2a having a grain size of 100 nm or more. Thereby, the mobility of carriers in the polysilicon film 2a can be improved, and the device characteristics can be improved.

[0005]

However, irradiation of the laser beam causes projections to be formed on the surface of the polysilicon film 2a, so-called surface roughness. This is probably because the silicon film 2 is heated to a considerably high temperature. Therefore, when an element such as a transistor is formed on the polysilicon film 2a, there is a problem that a focus shift in photolithography or an abnormal diffusion in diffusion of a conductive impurity may occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is intended to obtain a polysilicon film having a large grain size without causing surface roughness by irradiating a lower energy laser beam. It is intended to provide a film forming method capable of forming a film.

[0007]

The above object is achieved by the first invention.
A silicon oxide film for promoting crystallization on a glass substrate.
Forming and promoting the crystallization by chemical vapor deposition
Forming a silicon film on the silicon oxide film and heating
Enlarging the crystal grains of the silicon film.
The second problem is solved by a film forming method characterized in that
The silicon oxide film includes an O—H bond.
According to the film forming method described in the first invention,
A third aspect of the present invention is a crystal grain of the silicon film,
The heating to increase the
The film forming method according to the first or second invention, characterized in that
The crystallization promoting method according to the fourth aspect of the present invention,
The formation of the advanced silicon oxide film is performed by the thermal CVD method or the plasma.
The first to third aspects of the present invention are performed by a CVD method.
The method may be solved by the film forming method described in any one of
Forming the silicon oxide film for promoting crystallization according to the invention
Is any of TEOS, silane or disilane
Gas containing silicon and O_Two, H_TwoO, N _TwoO, NO_Two
Or O_ThreeUse any oxygen-containing gas
According to any one of the first to fourth inventions,
Is solved.

In the present invention, a silicon oxide film for promoting crystallization is formed on a glass substrate, and a silicon film is formed thereon. With such a structure, the silicon film on the crystallization-promoting silicon oxide film, which was amorphous immediately after the film formation, was subjected to a heat treatment so that the silicon film was more crystalline than when directly formed on the glass substrate. It was confirmed by experiments that the particle size of the grains was large.

In particular, the silicon oxide film for promoting crystallization is
When H bonds are included, the effect of increasing the average grain size of silicon crystal grains when heated is promoted.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 (a) to (d)
FIG. 2 is a cross-sectional view showing a method for forming a polysilicon film on a glass substrate according to an embodiment of the present invention. A quartz substrate is used as a glass substrate, and a well-known parallel plate type plasma CVD apparatus is used for forming an amorphous silicon film.

First, as shown in FIG.
+ O ₂ mixed gas plasma CVD (PECV
D method), a crystallization promoting silicon oxide film 12 having a thickness of about 200 nm is formed on a quartz substrate 11 having a thickness of 0.7 mm. Next, as shown in FIG. 1B, a silicon film 13 having a thickness of about 50 nm is formed on the crystallization promoting silicon oxide film 12 by a plasma CVD method using SiH ₄ gas. In this case, the silicon film 13 becomes amorphous.

Next, as shown in FIG.
By heating at 0 ° C., hydrogen (H) is removed from the silicon film 13. The reason is that if hydrogen remains in the silicon film 13, the hydrogen in the silicon film 13 expands and jumps out due to rapid heating when the next laser light is irradiated, and a hole is formed in the silicon film 13. Because. Next, as shown in FIG. 2, the amorphous silicon film 13 is irradiated with a laser beam having a frequency of 50 Hz and an energy density of one pulse of 306 mJ / cm ² . At this time, the quartz substrate 11 is moved in one direction in synchronization with the non-irradiation of the laser light.

As a result, as shown in FIG. 1D, the amorphous silicon is recrystallized, and a polysilicon film 13a composed of silicon crystal grains having a grain size of 100 nm or more is obtained. Further, since the energy of the laser beam is small, the surface of the polysilicon film 13a does not have surface roughness such as protrusions. The energy density of the laser beam is 350 m
J / cm ² or less, preferably 250 to 350 mJ / cm
A range of ² is good. Note that the energy density of the laser light is a set value on the side of the laser light generator, and the energy density on the sample side is not measured. However, if the energy density fluctuates due to the distance between the laser light source and the sample or the spread of the laser light. Conceivable.

FIG. 3A is a plan view showing the surface of the polysilicon film 13a after the heat treatment, which is observed by an electron microscope (SEM). For comparison, an SEM image of the surface of the polysilicon film 2a formed directly on the quartz substrate 11 is shown in FIG. Comparing the crystal particle diameters, the average particle diameter in the embodiment of the present invention was 100 nm or more, while the average particle diameter in the comparative example was about 50 nm.

Table 1 shows the presence or absence of OH and the average particle size (n
m) and Hall mobility (cm ² / Vsec). As a sample for measuring the hole mobility, a dose of 2 × 10
^This was prepared by ion-implanting phosphorus at ¹³ cm ^-2 and further annealing in nitrogen for 2 minutes. For comparison, a sample directly formed on a quartz substrate and PEC using silane gas
Samples formed on a crystallization promoting silicon oxide film formed by the VD method are also shown.

Here, the presence or absence of OH is determined by the well-known FT
Investigation was conducted by IR method (Fourier transform infrared absorption method). The average particle diameter was determined by counting the number of crystal grains in the survey range and using the formula of survey area / number. As shown in Table 1, O
In a silicon oxide film for promoting crystallization containing -H bonds,
Both the average grain size and the hole mobility of the crystal grains after heating can be increased. The content of O—H bond is 10 pp
m or more is preferable.

[0017]

[Table 1]

In some cases, a silane gas (SiH ₄ ) or the like which does not form an O—H bond may be used. Compared with the case where a film is formed, the crystal grains can be increased by heating for recrystallization, and the hole mobility can be increased. In the above embodiment, the PEOS using TEOS gas is used.
Although a crystallization promoting silicon oxide film formed by a CVD method is used, the method is not limited to this, and any method capable of forming an O—H bond may be used.

Furthermore, silicon-containing materials such as silane or disilane are included.
Using a gas, O as an oxidizing gas _Two, H_TwoO, N
_TwoO, NO_TwoOr O_ThreeOxygen-containing gas such as
No. Also, for crystallizing the amorphous silicon film,
Laser light is used as the heating means,
A child wire or other energy supply means may be used.

[0020]

As described above, in the present invention, a crystallization promoting silicon oxide film is formed on a glass substrate, a silicon film is formed thereon, and then the crystal grain size of the silicon film is increased by heating. doing. Therefore, the silicon film on the crystallization-promoting silicon oxide film is amorphous immediately after being formed, but when heated, the average particle size of silicon crystal grains of the silicon film is increased by the action of the crystallization-promoting silicon oxide film. Can be increased. In particular, when the crystallization promoting silicon oxide film contains an O—H bond, the effect of increasing the average grain size of silicon crystal grains is promoted.

[Brief description of the drawings]

FIGS. 1A to 1D are cross-sectional views illustrating a method for forming a polysilicon film according to an embodiment of the present invention.

FIG. 2 is a view showing a laser light irradiation method used for a polysilicon film forming method according to an embodiment of the present invention.

FIG. 3A is a plan view showing the result of observing the surface of a polysilicon film according to an embodiment of the present invention with an electron microscope, and FIG. 3B is a view showing the result of comparative observation; is there.

FIGS. 4A to 4C are cross-sectional views illustrating a method of forming a polysilicon film according to a conventional example.

[Explanation of symbols]

 11 quartz substrate, 12 crystallization promoting silicon oxide film, 13 amorphous silicon film, 13a polysilicon film.

Claims (5)

[Claims] A step of forming a silicon oxide film for promoting crystallization on a glass substrate; a step of forming a silicon film on the silicon oxide film for promoting crystallization by chemical vapor deposition; and heating the silicon film. A step of enlarging the crystal grains of the film. 2. The method according to claim 1, wherein the silicon oxide film includes an O—H bond. 3. The film forming method according to claim 1, wherein the heating for enlarging the crystal grains of the silicon film is performed by irradiating a laser beam. 4. The film forming method according to claim 1, wherein the silicon oxide film for promoting crystallization is formed by a thermal CVD method or a plasma CVD method. 5. The method for forming a crystallization promoting silicon oxide film includes forming a silicon-containing gas, which is one of TEOS, silane and disilane, and O ₂ , H ₂ O, N ₂ O, and NO _2.
5. The film forming method according to claim 1, wherein an oxygen-containing gas which is one of O ₃ and O ₃ is used.