JP2003282433A - Polycrystalline silicon film and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that crystallinity as a film cannot be improved since a conventional polycrystalline silicon film contains a large amount of amorphous constituent even after laser annealing. <P>SOLUTION: The gas seed of a halogen-based silicon raw material is used, the temperature of a substrate 4 is set to 150 to 200°C for carrying out a plasma CVD method, and an amorphous silicon film 5a having a crystalline nucleus is formed on the substrate 4. After that, a laser beam 24 having an energy density of 300 mJ/cm<SP>2</SP>or smaller is irradiated by laser annealing. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polycrystalline silicon film having excellent crystallinity and a method for producing the same.

[0002]

2. Description of the Related Art For example, in the production of crystallized silicon for thin film transistors used in liquid crystal display devices, plasma CV using silane (SiH ₄ ) gas as a raw material.
By applying the D method and suppressing the amount of diluted hydrogen at a high substrate temperature of about 400 ° C., an amorphous silicon film is grown on the glass substrate or the SiO ₂ film, and the amorphous silicon film is laser-annealed by laser annealing. Crystallization and a silicon film are obtained by irradiating with light.

However, the polycrystalline silicon film produced by such a method contains a large amount of amorphous components even after laser annealing, and the crystallinity of the film cannot be increased. The present inventors have found that this amorphous component is due to an amorphous silicon film grown by the plasma CVD method, and particularly, the conditions for growing the amorphous silicon film by the plasma CVD method, and It was discovered that there is a problem in compatibility with the conditions for obtaining crystallization and the silicon film.

When the gas species used in the plasma CVD method is a silane gas, a crystal nucleus cannot be formed in an amorphous silicon film having a film thickness of 100 nm or less at a substrate temperature of 200 ° C. or less, but a halogen gas is used. It is known that the use thereof makes it possible to form crystal nuclei at a low temperature of 150 to 200 ° C. or lower (Ref. Takash.
i Arai and Hajime Shirai,
J, Appl, Phys. 80 (1996) 497
6).

The present invention has been made in order to solve the problems of the conventional method, and by using a halogen-based silicon raw material, the substrate temperature is 150 to 200.
A plasma CVD method is performed at a low temperature of about 0 ° C. to form fine crystal nuclei, and then a laser beam having a low energy density of 300 mJ / cm ² or less is irradiated. This allows
It is an object of the present invention to provide a polycrystalline silicon film having a small amount of amorphous components and a high degree of crystallinity.

[0006]

The present invention has been made in view of the above-mentioned conventional technical problems, and the structure thereof is as follows.
It is as follows. The invention of claim 1 uses a gas species of a halogen-based silicon raw material, and the substrate temperature is 150 to 200 ° C.
The plasma CVD method is performed in this range to form an amorphous silicon film having crystal nuclei on the substrate, and then the amorphous silicon film is irradiated with laser light having an energy density of 300 mJ / cm ² or less by laser annealing, It is a polycrystalline silicon film characterized by being a silicon film having a small amount of amorphous components and a high degree of crystallinity.
According to the invention of claim 2, an amorphous silicon film containing crystal nuclei is formed to a film thickness of 100 nm or less using a halogen-based silicon raw material as a gas species used in the plasma CVD method, and then the amorphous silicon film is irradiated with laser light. A method for producing a polycrystalline silicon film, which comprises forming a polycrystalline silicon film having a small amount of amorphous components and excellent crystallinity. According to a third aspect of the present invention, there is provided a method for producing a polycrystalline silicon film, which comprises forming an amorphous silicon film on a substrate by plasma CVD and then irradiating the amorphous silicon film with laser light to form a crystallization / silicon film. , In the initial process of forming the amorphous silicon film,
A polycrystalline silicon film having excellent crystallinity is formed by forming crystal grains to be crystal nuclei using a gas species of a halogen-based silicon raw material and then irradiating the crystal grains with laser light. This is a method for producing a crystalline silicon film.

[0007]

1 and 2 show an apparatus used for manufacturing a polycrystalline silicon film according to the present invention. For the polycrystalline silicon film, a CVD method is applied using a chlorine-based silicon raw material as a gas species (raw material gas) to form an amorphous silicon film (a-Si film) containing fine crystal nuclei on a substrate. After that, laser annealing is applied to the substrate on which the crystal nuclei are formed to crystallize the a-Si film to form a polysilicon film (p-S).
i film). By changing the crystal nuclei into the p-Si film, it is possible to produce a silicon film having less amorphous components and high crystallinity.

As the CVD method, a plasma CVD method is used, and an amorphous silicon layer is formed on a glass substrate (thermally oxidized Si ₂ film) while directly growing silicon crystal nuclei. As the plasma CVD apparatus, the one of the capacitive coupling type parallel plate RF (frequency of high frequency power supply 13.56 MHz) shown in FIG. 1 was used. A cathode electrode 2 and an anode electrode 3 are arranged in parallel in a reaction vessel 1, and a substrate 5 is provided on the anode electrode 3.
Install.

In a state where the inside of the reaction vessel 1 is decompressed by a vacuum pump (not shown) connected to the exhaust pipe 7, an RF electric field is formed between the electrodes 2 and 3 by the RF power source 4, and the cathode is formed. The raw material gas of the chlorine-based mixed raw material made of the chlorine-based silicon raw material supplied from the gas introduction pipe 6 on the electrode 2 side is turned into plasma, and the raw material gas components are deposited to form a thin film. Reference numeral 8 is a heater for heating the substrate 5 to a predetermined temperature, and 9 is a lens for diagnosing the plasma state.

The specific production conditions of the polycrystalline silicon film by the plasma CVD apparatus here are 3 to 10 sccm (standard cc) of a chlorine-based mixed raw material as a gas species.
per minute), hydrogen 10 to 100 sccm,
Substrate temperature 150 to 200 ° C., pressure inside reaction vessel 1 150
˜600 mTorr, RF power 2˜100 W, deposition time 1˜120 minutes. Generally, since the vapor pressure of chlorine-based silicon raw material is high, it is maintained at 80 ° C. in a constant temperature bath (not shown) as raw material gas, and the flow rate is individually adjusted with a diluent gas (hydrogen gas) through a mass flow controller (not shown). After that, they were merged and introduced into the reaction vessel 1 as a uniform mixed gas.

The chlorine-based mixed raw material as the gas species includes a mixture of a plurality of types of chlorine-based silicon raw materials and a material of a single type of chlorine-based silicon raw material. Chlorine-based silicon raw materials include dichlorosilane (SiH ₂ Cl ₂ ),
Trichlorosilane (SiHCl ₃ ), silicon tetrachloride (S
iCl ₄ ) etc.

By applying the plasma CVD method under the above production conditions, an amorphous silicon film (a-Si film) containing crystal nuclei was formed on the substrate 5. This amorphous silicon film is made of microcrystalline silicon (a-Si / nc-S).
i), that is, Si nanocrystals having a diameter of several nanometers.

Then, the substrate 5 on which the a-Si film is formed
Laser anneal to. The apparatus used for laser annealing is shown in FIG. Laser light A generated by a laser oscillator 20 for generating an excimer laser composed of a pulse laser
1 is introduced into the optical system container 29, energy is automatically set by an attenuator (not shown), and the direction is changed by the reflection mirror 27, and shaped through the long-axis homogenizer 22a and the short-axis homogenizer 22b to make the intensity uniform. After changing the direction, the direction is changed again by the reflection mirror 28,
By passing the condenser lens 23, the major axis x the minor axis becomes about 2
Shaped into a square line beam 24 of 00 × 0.4 mm,
Irradiate the substrate 5. The substrate 5 is installed in the vacuum chamber (annealing chamber) of the laser annealing apparatus.

The line beam 4 is formed on the a-Si film 5a of the substrate 5.
Is irradiated, the a-Si film 5a is crystallized and p
-Si film 5b is formed. In order to crystallize the entire surface of the a-Si film 5a on the substrate 5, the substrate 5 is moved along the short axis of the line beam 24 at a feed pitch of 5 to 10% of the line axis short axis width per shot of the line beam 24. Move in the direction. When the minor axis width is 0.4 mm, the specific feed pitch is 2
It is 0 to 40 μm, and the number of times the substrate 5 is irradiated with laser light is 10 to 20 times.

Crystals grow by irradiating the substrate 5 a plurality of times. It is considered that the crystal growth is increased by the crystal grains in the a-Si film 5a being combined by the subsequent irradiation of laser light. In order to grow this crystal, it is necessary to irradiate the laser beam A1 so that the substrate 5 rises from a cooled (normal temperature) state to near the melting temperature.

The crystallinity of the p-Si film 5b in such crystallization / manufacture of a silicon film largely depends on the energy density of the laser beam A1. Generally, the energy density is too low or too high. Is not good. For this reason,
A plurality of p-Si are formed by changing the energy density of the laser beam A1.
The film 5b is produced, and the p-Si film 5b is directly observed with an SEM (scanning electron microscope) or the like to determine the optimum energy density from the one having good crystallinity, and the energy density on the substrate 5 is determined. The entire surface of the Si film 5a is crystallized.

Under the above production conditions, however, the plasma CV is used.
When the D method is applied to form the a-Si film 5a on the substrate 5 and the laser annealing is applied to the a-Si film 5a, the generally used 400 mJ / cm ² is used.
Irradiation with laser light having a lower energy density, especially 3
Laser light A1 with an energy density of 00 mJ / cm ² or less
By irradiating with, it is possible to form the p-Si film 5b having less amorphous component and high crystallinity.

Actually, the capacitive coupling type parallel plate R shown in FIG.
Using a F (13.56 MHz) plasma CVD apparatus, chlorine-based mixed raw material 5 sccm (standard c)
c per minute), hydrogen 50 sccm, substrate 5 temperature 200 ° C., pressure 400 mTorr, RF power 5
0 W, deposition time 60 minutes, substrate 5 containing crystal nuclei a
The -Si film 5a (a-Si / nc-Si film) was formed.
The reaction vessel 1 during film formation was maintained at about 80 ° C. with a ribbon heater. This is the implementation condition of the plasma CVD apparatus.

Amorphous layer (a-Si / nc-) containing crystal nuclei formed under the conditions of implementation of this plasma CVD apparatus.
The thickness of the Si layer) is about 40 nm. The density and size of the crystal nuclei to be directly grown can be controlled by changing the implementation conditions within the range of the above production conditions.

After that, the substrate 5 having the a-Si film 5a formed thereon was subjected to laser annealing. That is, a of the substrate 5
Performing laser annealing in low energy density of about 300 mJ / cm ² to -Si film 5a, were polycrystalline amorphous silicon. As a result, the results shown in FIGS. 3 to 8 were obtained, and it was confirmed that a polycrystalline silicon film having a small amount of amorphous components and a high degree of crystallinity can be obtained.

Silane (SiH ₄ ) is used as a conventional gas species (source gas), a CVD method is applied to form crystal nuclei on the substrate, and then laser annealing is applied to a-Si.
In the production method (conventional product) of crystallizing the film into a p-Si film, a crystal nucleus cannot be formed in an a-Si film having a film thickness of 100 nm or less at a substrate temperature of 200 ° C. or less. That is, it is empirically known that in the growth process, an incubation layer mainly composed of amorphous is formed up to a thickness of about 100 nm, and then a crystal layer, that is, a layer that can be changed into polysilicon grows.

On the other hand, when a chlorine-based mixed raw material is used as a gas species, crystal nuclei are formed in the a-Si film from the initial growth stage, despite the low substrate 5 temperature in the range of 150 to 200 ° C. Formation is observed. A- in the initial stage of this growth
It has been confirmed by observation with an atomic force microscope (AFM) and a transmission electron microscope (TEM) that the Si film is an island-shaped growth of crystal grains having a size of 10 to 30 nm. Therefore, the a-Si film having this crystal nucleus is microcrystalline silicon (a-Si / nc-Si). The density of this crystal nucleus,
The size and height can be controlled by changing reaction conditions (RF power density, RF plasma supply time ON / OFF ratio, reaction pressure, substrate temperature, film formation time, hydrogen flow rate ratio, etc.). By utilizing these controlled crystal grains as a seed crystal, it is possible to promote crystallization of polysilicon and increase in grain size by irradiation with laser light.

As a method of producing a polycrystalline silicon film having an excellent crystallinity, a plasma CVD method is used in the process of application.
Specifically, there are two. The first method is plasma CVD
A mixed gas of chlorine-based silicon raw material (chlorine-based mixed raw material) and hydrogen is used as a gas species of the method, and the entire amorphous silicon film is formed to have a predetermined film thickness (about 40 nm) of 100 nm or less. This is a method of forming crystal grains serving as crystal nuclei throughout. As the chlorine-based silicon raw material of the first method, silicon tetrachloride (Si
Cl ₄ ) is suitable. The second method uses a mixed gas of chlorine-based silicon raw material (chlorine-based mixed raw material) and hydrogen as a gas species of the plasma CVD method in the initial process of forming an amorphous silicon film to form crystal grains to be crystal nuclei. It is formed as an initial film, and then an amorphous silicon film is formed on the initial film by an arbitrary method to a predetermined film thickness. As an arbitrary method for forming an amorphous silicon film on this initial film, a silane plasma CVD method, a sputtering method, an electron beam evaporation method, or the like can be widely applied.

By irradiating the crystal grains of the amorphous silicon film formed to have a predetermined film thickness by the first and second methods with laser light, recrystallization is performed and a polycrystalline silicon film having excellent crystallinity is obtained. can do. In the polycrystalline silicon film based on the second method, columnar crystals grow from the initial film with respect to the entire initial film having crystal nuclei and any amorphous silicon film formed thereon by irradiation of laser light. With respect to the reduction of the amorphous component and the improvement of the crystallinity, it is possible to obtain almost the same effect as the polycrystalline silicon film based on the first method.

That is, in both the first and second methods, compared with the conventional growth from a silane system (SiH ₄ ), the amount of amorphous components is small and the amount of amorphous components is small by evaluation by Raman spectrum and spectroscopic ellipsometry. It can be confirmed that the polycrystalline silicon film has an excellent degree of conversion. In particular, irradiation with laser light having an energy density lower than about 400 mJ / cm ² which is generally used, above all, 300
It has a feature that the half-width is narrow even under a low laser irradiation condition of mJ / cm ² or less.

In FIG. 3, after the amorphous silicon film is formed by the first method, the crystallization / silicon film (p-
It is a Raman-measured scattering spectrum for a polycrystalline silicon film having a Si film formed thereon. That is, an a-Si film (a-Si / nc-) formed using a chlorine-based silicon raw material.
Si / glass) 280, 300, 320 and 3
It is a Raman scattering spectrum from the p-Si film laser-crystallized by each energy density of 60 mJ / cm < ² >. The horizontal axis represents wave number (cm ⁻¹ ) and the vertical axis represents Raman intensity (arbitrary unit).

[0027] In FIG 3, the half-value width of the TO phonon peak due to crystalline silicon found at the wave number 515 cm ^-1 (optical phonon peak) is approximately 5.2 cm ^-1, the half width in the case of single crystal silicon Is virtually equal to.
On the other hand, FIG. 9 and FIG. 10 show p-Si obtained by laser crystallization of an a-Si film formed from a conventional silane-based gas.
The Raman scattering spectrum of the film was measured by Raman, and the full width at half maximum of the p-Si film was 5.5 to 5.8 cm ^-1 . 9 and 10 indicate the energy density (mJ / cm ² ) of the laser light irradiated by laser annealing. Thus, 400 mJ /
In the polycrystalline silicon film obtained by irradiation with laser light having an energy density lower than cm ^{2, the} polycrystalline silicon film based on the above implementation conditions has a smaller full width at half maximum of the TO phonon peak. Then, it can be seen that the amorphous component is small and the crystallinity is high. This uses a gas type of chlorine-based mixed raw material (chlorine-based silicon raw material),
This is related to the fact that the plasma CVD method was performed under the above-mentioned execution conditions, and the same applies to the low laser irradiation condition of 300 mJ / cm ² or less.

FIGS. 4 and 5 show Raman measurements on a polycrystalline silicon film having a crystallized silicon film (p-Si film) formed after forming an amorphous silicon film by the first method. It is a Raman scattering spectrum. 4 and 5
From the energy density (Power) of the laser light to 32
In the case of 0 mJ / cm ² and 360 mJ / cm ² , the ratio of the amorphous component appearing at a wave number of 480 cm ⁻¹ or less is the polycrystalline silicon film (a-Si / nc-Si: H ( Cl)) is more
Compared with a conventional p-Si film based on only an a-Si film formed from a silane-based gas (shown by solid lines in FIGS. 4 and 5),
It turns out that there are few. The ratio of the amorphous component appearing at a wave number of 480 cm ^-1 or less is smaller than that of a p-Si film (shown in FIGS. 9 and 10) based only on an a-Si film formed from a conventional silane-based gas. It can be seen from the comparison between FIG. 3 and FIG. In particular, it can be understood that the proportion of the amorphous component is small when laser light having a low energy density of 300 mJ / cm ² or less is irradiated by laser annealing.

Further, FIGS. 6 to 8 show p-Si based on microcrystalline silicon (a-Si / nc-Si) under the above-mentioned conditions.
The analysis result of the spectroscopic ellipsometry of the film and the p-Si film based on the conventional method (a-Si) is shown. The horizontal axis represents energy (eV) and the vertical axis represents epsilon 2 (dimensionless). It should be noted that the numbers shown with P in FIGS. 6 to 8 indicate the energy density (mJ) of the laser light irradiated by laser annealing.
/ Cm ² ).

From the analysis result, the activation energy is 3.3.
At eV (wavelength region corresponding to energy value of 3.3 eV) and 4.2 eV (wavelength region corresponding to energy value of 4.2 eV), E ₁ and E ₂ transitions caused by optical transition of crystalline silicon The fine structure based on it is clearly observed. Therefore, it can be confirmed from another aspect that the crystallinity of the polycrystalline silicon film under the above-mentioned execution conditions is high. Figure 6
In FIG. 8, the solid line indicates the polycrystalline silicon film (a-Si / nc-Si) based on the above implementation conditions, and the broken line indicates the conventional method (a-Si). As the surface roughness increases, the value (dimensionless) of the epsilon 2 (Epsilon 2) for reflection becomes smaller.

In the above-mentioned one embodiment, the chlorine-based silicon
Raw material, namely dichlorosilane (SiH₂Cl₂),
Lichlorosilane (SiHCl₃), Silicon tetrachloride (Si
Cl _Four) Together with laser annealing
A crystalline silicon film was prepared, but halogen-based materials such as fluorine-based materials were used.
General silicon material (halogenated silicon material) is used
However, it is possible to create an amorphous layer containing similar crystal nuclei.
Is. Therefore, even with regard to thermal annealing,
Solid phase growth can be promoted.

[0032]

As can be understood from the above description,
According to the polycrystalline silicon film and the method for producing the same according to the present invention, the crystal nuclei are directly grown in the amorphous film,
By using the halogen-based silicon raw material as the gas species, it becomes possible to produce a polycrystalline silicon film having a small amorphous component and a high crystallinity after the annealing treatment.

According to the first aspect of the present invention, the substrate temperature required for annealing is lower than that in the conventional method, so that the burden on the annealing chamber can be reduced. In addition, in the case of laser annealing, crystallization can be performed by laser irradiation with a low energy density, so that a low output laser device can be used. As a result, it is possible to achieve an effect that the entire apparatus for producing the polycrystalline silicon film can be made simple in structure and inexpensive.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a plasma CVD apparatus used for producing a polycrystalline silicon film according to an embodiment of the present invention.

FIG. 2 also shows a laser annealing apparatus, (a) is a front view and (b) is a right side view.

FIG. 3 is a diagram showing a Raman scattering spectrum of the polycrystalline silicon film.

FIG. 4 is a diagram showing a Raman scattering spectrum of a polycrystalline silicon film.

FIG. 5 is a diagram showing a Raman scattering spectrum of a polycrystalline silicon film.

FIG. 6 is a diagram showing the results of spectroscopic ellipsometry analysis of a polycrystalline silicon film according to the method of the present invention and a polycrystalline silicon film based on the conventional method.

FIG. 7 is a diagram showing the analysis results of spectroscopic ellipsometry of the polycrystalline silicon film according to the method of the present invention and the polycrystalline silicon film based on the conventional method.

FIG. 8 is a diagram showing the analysis results of spectroscopic ellipsometry of a polycrystalline silicon film according to the method of the present invention and a polycrystalline silicon film based on the conventional method.

FIG. 9 is a diagram showing a Raman scattering spectrum of a conventional polycrystalline silicon film.

FIG. 10 is a diagram showing a Raman scattering spectrum of a conventional polycrystalline silicon film.

[Explanation of symbols]

1: reaction vessel, 2: cathode electrode, 3: anode electrode,
4: RF power source, 5: substrate, 5a: a-Si film (a-Si
/ Nc-Si film), 5b: p-Si film (Si film), 6:
Gas introduction pipe, 7: exhaust pipe, 8: heater, 20: laser oscillator, 22a: long axis homogenizer (homogenizer), 22b: short axis homogenizer (homogenizer), 20: laser oscillator, 20 :, A1: laser light.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoyuki Kobayashi             2-2-1 Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa               Japan Steel Works, Ltd. (72) Inventor Hideaki Kusama             2-2-1 Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa               Japan Steel Works, Ltd. F-term (reference) 4K030 AA03 AA17 BA30 CA06 DA08                       FA01 JA01 LA15                 5F045 AA08 AB04 AC05 AD05 AE19                       AF07 BB12 BB18 CA15 DP03                       EF02 EH14 HA18                 5F052 AA02 BA02 BA07 BB07 DA02                       DB03

Claims (3)

[Claims] 1. A plasma CVD method is performed using a halogen-based silicon source gas species at a substrate temperature in the range of 150 to 200 ° C. to form an amorphous silicon film having crystal nuclei on the substrate, and then the amorphous silicon film. A polycrystalline silicon film, characterized in that the film is irradiated with laser light having an energy density of 300 mJ / cm ² or less by laser annealing to obtain a silicon film having a small amount of amorphous components and a high degree of crystallinity. 2. An amorphous silicon film containing crystal nuclei is formed to a film thickness of 100 nm or less using a gas species used in the plasma CVD method as a halogen-based silicon raw material, and then the amorphous silicon film is irradiated with laser light to obtain an amorphous component. 1. A method for producing a polycrystalline silicon film, which is characterized in that the polycrystalline silicon film has less crystallinity and is excellent in crystallinity. 3. A method for producing a polycrystalline silicon film, comprising forming an amorphous silicon film on a substrate by plasma CVD and then irradiating the amorphous silicon film with laser light to form a polycrystalline silicon film. In the initial process of forming a silicon film, a crystal grain serving as a crystal nucleus is formed by using a gas species of a halogen-based silicon raw material,
Then, a method for producing a polycrystalline silicon film, characterized by irradiating crystal grains with laser light to obtain a polycrystalline silicon film having excellent crystallinity.