JP3408399B2 - Method of forming silicon film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a silicon film used for semiconductor devices such as solar cells and thin film transistors.

[0002]

2. Description of the Related Art Conventionally, polycrystalline silicon (hereinafter referred to as "poly-Si") is used.
For forming a film or an amorphous silicon (hereinafter referred to as “a-Si”) film at low temperature, plasma CVD (Chemic
al Vapor Deposition) method, thermal CVD method or photo CVD
The method is used. Generally, plasma C from the vapor phase
The VD method has problems such as a low film formation rate, powder generation in the gas phase to contaminate the apparatus, and a complicated and expensive apparatus such as a high frequency generator is required. Also, the heat C from the gas phase
In the VD method, when a film having a thickness of several μm is formed at a high speed, 60
It is necessary to form the film at a temperature higher than 0 ° C., and an expensive heat-resistant substrate must be used.

In addition to the above method, there is also a method of solid-phase crystallization of a-Si at low temperature using a metal such as nickel as a catalyst (see Japanese Patent Laid-Open No. 6-244103). However, it is not suitable for forming a thick film because it is slow.

Therefore, as a method of forming a film from a liquid phase which eliminates these drawbacks, a method of applying a high-order silane solution to a substrate and irradiating it with ultraviolet light to form a film (Japanese Patent Laid-Open No. 5-144741)
(See Japanese Patent Laid-Open No. 7-267621), or a method of forming a film by applying a high-order silane solution to a substrate and going through a thermal history including a temperature raising process (see Japanese Patent Laid-Open No. 7-267621).

However, in these methods, when the temperature of the substrate is set to an appropriate film-forming temperature, the boiling point of the high-order silane is low (see Table 1), so that the high-order silane evaporates before the completion of the polymerization. It becomes difficult to form a film thicker than 1 μm and adjust a desired film thickness.

[0006]

[Table 1]

In general, a method of forming a film from a liquid phase by applying a high-order silane solution can form a film at a higher speed than a method of forming a film from a gas phase. However, since the high-order silane has a low boiling point as described above, the high-order silane liquid evaporates during film formation, and the formed film becomes considerably thinner than the coating film thickness.
An arbitrary film thickness cannot be obtained. Therefore, it has been desired to perform film formation at high speed and improve reactivity at low temperature.

Further, in order to form a crystalline silicon film having relatively good crystallinity at a high speed, it is generally necessary to form the film at a temperature higher than 600.degree. However, for example, if an inexpensive substrate made of non-alkali glass or the like is used, there is a problem in heat resistance, so that the film must be formed at a temperature lower than 600 ° C., and a crystalline silicon film with good crystallinity is obtained. I can't.

Therefore, in view of the above problems, an object of the present invention is to provide a method of forming a silicon film at a high speed and at a low temperature while maintaining the quality as a device.

[0010]

A method for solving the problems according to the present invention is to thermally decompose a mixture of a solution of higher silane and a catalyst to form a silicon film on a substrate. Also,
The mixture is photolyzed by irradiating with light having a wavelength shorter than 400 nm to form a silicon film on the substrate.

The higher silane has the general formula Si _n H
_{2n + 2} order silane (n is an integer of n ≧ 3) represented by or the formula _{Si n H l X m (X} , is either chlorine, fluorine, bromine or iodine, l + m = 2n + 2, n Is n ≧ 3
Halogenated higher-order silane represented by As the catalyst, a catalyst containing at least one of nickel, iron, cobalt, or platinum or a solution of this catalyst is used, and in the case of the solution, the solvent of the catalyst is a solvent in which the higher silane is soluble and The boiling point may be lower than the temperature at which the silicon film is formed. According to this method, the silane can be decomposed by the action of the catalyst to form a silicon film having a desired thickness at a higher speed and at a lower temperature than ever before.

Particularly, in the formation of the crystalline silicon film,
A good crystal can be grown by applying a mixture having a high catalyst concentration on a substrate to form a crystal nucleus generation layer, and applying a mixture having a low catalyst concentration on this layer.

If atomic hydrogen gas is supplied to the substrate during thermal decomposition or photolysis, the polymerization can be promoted and the film quality can be improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

To form a silicon film according to the present invention,
First, a substrate such as glass placed in an inert gas atmosphere is coated with a mixture of a solution of higher silane and a catalyst. Alternatively, a mixture of a high order silane solution and a catalyst solution may be applied.

The higher silane has the general formula Si _n H
_The one represented by _{2n + 2} (n is an integer of n ≧ 3) is used,
Specifically, trisilane (Si ₃ H ₈ ), tetrasilane (Si ₄ H ₁₀ ), pentasilane (Si ₅ H ₁₂ ), hexasilane (Si ₆ H ₁₄ ), heptasilane (Si ₇ H ₁₆ ), octasilane (Si ₈ H ₁₂ ). ₁₈ ), nonasilane (Si ₉ H ₂₀ ) and the like.
Alternatively higher silane of the general formula Si _n H _l X _m (X is either chlorine, fluorine, bromine or iodine, l + m = 2
n + 2, n is an integer of n ≧ 3, and may be a halogenated high-order silane such as pentasilane chloride. In addition, high-order silane or halogenated high-order silane is 2
You may use 1 or more types.

As the catalyst, a substance containing at least one of nickel, iron, cobalt or platinum or a solution thereof is used. Specifically, an organic salt of nickel,
Nickel is included in the composition of halogenated salts, etc.
Those that dissolve more than ppb are desirable.

Here, although it is possible to directly mix the high-order silane and the catalyst, it is dangerous to maintain a highly reactive state. Therefore, an organic solvent for the catalyst is used in the introduction tube or It may be mixed on the substrate. In this case, the organic solvent is a solvent in which the high-order silane is soluble, has low reactivity with the high-order silane, and has a boiling point lower than the film forming temperature, preferably lower than the boiling point of the high-order silane used.

The catalyst and the organic solvent can be set in any combination, and examples of the catalyst include nickel fluoride, nickel chloride, nickel nitrate, nickel acetate, nickel carbonate and the like. Further, examples of the organic solvent include C _a H _b (5 ≦ a ≦ 1) such as pentane, hexane, cyclohexane, heptane, octane, isooctane, benzene, ethylbenzene, toluene or xylene.
0,12 ≦ b ≦ 24) hydrocarbons and diethyl ether represented by, diisopropyl ether, acetone, methyl ethyl ketone, methanol, _{ethanol, C a H b O c (} 1 ≦ a ≦ 8,4 ≦ such propanol or butanol b
Examples include ethers, ketones, and alcohols represented by ≦ 14, 1 ≦ c ≦ 3).

The concentration of the high order silane in the mixed solution of the high order silane and the catalyst is preferably more than 50% by weight. Since the organic solvent remains by increasing the high-order silane concentration as high as possible, the amounts of carbon and oxygen taken into the film can be reduced.

The method of coating the high-order silane on the substrate includes
There are a spin coating method, a dip coating method, a spray coating method, a bar coating method and a curtain coating method. In the case of the spin coating method which is generally used, the rotation speed of the spinner is 100 to 10,000 rpm, preferably 300 to
Use 6,000 rpm. Further, at this time, as a pretreatment for coating, heating to a temperature higher than the boiling point of the organic solvent to evaporate the organic solvent in advance to remove the organic solvent, or partially polymerize the higher silane by a method such as light irradiation. Treatment such as increasing the viscosity of the higher order silane may be performed.

Next, a predetermined silicon film is formed by thermal decomposition by heating or photo decomposition by irradiation of light.
Examples of the heating method include heating with a heater provided on a table holding the substrate and heating with an infrared lamp.
Further, in the method of photolysis by irradiation with ultraviolet light, it is carried out in a gas atmosphere which is inactive with high-order silanes such as helium, neon, argon, nitrogen or hydrogen. As the light source for the irradiation light, an ultraviolet light source with a wavelength shorter than 400 nm is used because the higher order silane absorbs energy and decomposes. For this, for example, low-pressure mercury lamp light, discharge light of hydrogen or deuterium, or rare gas such as argon, krypton, or xenon, excimer laser light, or the like is used.

When the above method is used, the silane can be decomposed by the action of a catalyst to form a silicon film at a higher speed and at a lower temperature than ever before. In this case, when the substrate temperature is higher than about 150 ° C., an a-Si film is obtained, and further about 50
When the temperature is higher than 0 ° C, a poly-Si film can be obtained. The thickness of the obtained silicon film can be arbitrarily set to about 5 to 50 μm by selecting the coating method.

On the other hand, nickel mixed with the higher order silane is
Although it functions to lower the decomposition temperature of silane, it is not preferable as a semiconductor material. For example, when used as a solar cell, the nickel concentration in the film is 1 × 10 ¹⁹ /
It is preferably lower than cm ³ . In particular, Ni / Si after dissolving a trace amount of catalyst in an organic solvent and mixing with high-order silane
It is more preferable to adjust the ratio to be smaller than 10 ^-2 to 10 ^-8 , especially 10 ^-5 .

Further, during the formation of the crystalline silicon film, crystals grow from the crystal nuclei existing at the initial stage of film formation, but if the generation of the crystal nuclei is controlled, the crystallinity will be affected. Therefore, as shown in FIG. 2, a mixed liquid (Ni / Si ≧ 10 ⁻⁵ ) having a high catalyst concentration is applied onto the substrate A to form a first coating layer B (crystal nucleus generating layer), and crystal nuclei are formed. To generate. Next, on the first coating layer B, a mixed solution (Ni
/ Si <10 ⁻⁵ ) to form a second coating layer C.
As a result, the portion serving as the nucleus of crystal growth in the arrow direction can be limited to the inside of the first coating layer B, and the crystallinity can be improved.

Further, since defects are generated by desorption of hydrogen during film formation at a high temperature, the pressure is reduced to about 0.01 to 10 Torr when the temperature is raised, and atomic hydrogen gas is supplied to the substrate. To obtain this atomic hydrogen, for example, a method of obtaining hydrogen gas by high-frequency discharge such as microwave, a method of irradiating hydrogen gas with high energy rays such as ultraviolet rays, heating a metal such as tungsten, There is a method of obtaining by contact with the surface. By these methods, it is possible to promote the polymerization and improve the film quality.

[0027]

EXAMPLES Examples and comparative examples in which a silicon film is formed by carrying out the method of the present invention will be described below. The physical properties of the films formed in Examples and Comparative Examples were measured as follows, and the measurement results are shown in Table 2.

1. Photoconductivity (AM 1.5, 100mW
Irradiation) 2. Dark conductivity 3. Optical gap

[0029]

[Table 2]

<Embodiment 1> FIG. 1 shows the configuration of an experimental apparatus of Embodiment 1. This experimental apparatus includes a coating chamber 1 and a film forming chamber 2, which are connected via a gate valve 3. In the coating chamber 1, a dropping line 4 for dropping a high-order silane solution, a dropping line 5 for dropping a catalyst solution, a spin coater 7 holding a substrate 6 and rotated by a motor (not shown), and an exhaust line. 8 are provided. The dripping lines 4 and 5 are joined in the middle of the lines and are guided to the coating chamber 1 as one line. Further, in the film forming chamber 2, a heater 9 for heating the substrate 6 and a gas supply line 1 for supplying an inert gas or the like.
0 and an exhaust line 11 are provided.

In this example, pentasilane (Si ₅ H ₁₂ ) was used as the high order silane, and nickel fluoride was dissolved in diethyl ether as the catalyst.

The procedure for forming the silicon film will be described below.
In the coating chamber 1, 0.5 ml of a solution of pentasilane was dropped onto the substrate 6 from the dropping line 4 and 0.05 to 0.5 ml of a solution of nickel fluoride was dropped from the dropping line 5. Then, the spin coater 7 was rotated at a predetermined rotation speed or for a predetermined time to form a coating film. Table 2 shows the conditions of nickel fluoride solution and spin coating mixed with 1 ml of pentasilane.

Next, the film forming chamber 2 is evacuated to 1 × 10 ^-6 Torr, and then helium gas is supplied from the gas supply line 10 to 76
It was introduced up to 0 Torr. After moving the substrate 6 to the film forming chamber 2 through the gate valve 3, while introducing helium gas at 0.5 l / min, the substrate 6 is heated by the heater 9 at a rate of 100 ° C./min to 200 ° C., The substrate temperature was kept for 20 minutes to form an a-Si film on the substrate 6.

Example 2 A poly-Si film was formed in the same manner as in Example 1 except that the substrate 6 was heated by the heater 9 at a rate of 100 ° C. per minute to 500 ° C. and heated for 60 minutes. Formed.

<Example 3> An a-Si film was formed in the same manner as in Example 1 except that pentasilane chloride was used as the higher order silane.

Example 4 As shown in FIG. 2, a mixture having a large catalyst concentration was applied to form a first coating layer B, and the temperature was raised to 500 ° C. at a rate of 100 ° C./min. It was heated for minutes to form crystal nuclei (see Example 4-1 in Table 2). In addition, the substrate A
After cooling, a mixture having a low catalyst concentration was applied to form a second coating layer C, which was heated at a rate of 100 ° C. per minute to 500 ° C. and heated for 60 minutes (in Table 4-2, Example 4-2). Others were the same as in Example 1 to form a crystalline silicon film having good crystallinity.

<Embodiment 5> As shown in FIG. 3, instead of thermally decomposing, a low pressure mercury lamp 12 as a light source is provided in the film forming chamber 2.
An a-Si film was formed in the same manner as in Example 1 except that the low pressure mercury lamp 12 was used to irradiate light having a wavelength shorter than 400 nm to perform photolysis using the experimental apparatus provided with.

Example 6 As shown in FIG. 4, the film forming chamber 2
In the experimental apparatus equipped with the hydrogen gas introduction line 13 and the microwave generation chamber 14 provided in the middle of the line 13, the pressure is reduced to 1 Torr when the temperature is raised, and the microwave generated from the microwave generation chamber 14 is used. An a-Si film was formed in the same manner as in Example 1 except that the atomic hydrogen gas to which the energy had been applied was supplied onto the substrate 6.

<Embodiment 7> As shown in FIG. 5, spraying is performed by irradiating a solution with a spray gun 15 using an experimental apparatus having a spray gun 15 at the tip of the coating chamber 1 of the dropping lines 4 and 5. An a-Si film was formed in the same manner as in Example 1 except that the a-Si film was applied by the coating method.

<Comparative Example 1> The same procedure as in Example 1 was carried out except that only the solution of the higher order silane was applied without mixing the catalyst, but no silicon film was formed.

<Comparative Example 2> The procedure of Example 2 was repeated except that only the solution of the high-order silane was applied without mixing the catalyst.
A Si film was formed.

From the above results, when the catalyst is not mixed as in Comparative Examples 1 and 2, the silicon film is not formed at the film forming temperature of about 200 ° C., and a- is formed at the film forming temperature of about 500 ° C.
A Si film was formed. On the other hand, especially in Example 2, under the same film forming conditions as in Comparative Example 2, poly
-Si film was formed, conductivity was improved and optical gap was reduced. In addition, in Example 4, crystallization was promoted to form a silicon film having good crystallinity, and the conductivity and the optical gap were improved.

The present invention is not limited to the above embodiment, and many modifications and changes can be added to the above embodiment within the scope of the present invention.

[0044]

As described above, according to the present invention, a solution of a high order silane and a catalyst are mixed and pyrolyzed or photolyzed, so that a-Si is produced at a higher speed and a lower temperature than before by the action of the catalyst. A film, a poly-Si film, or a crystalline silicon film with favorable crystallinity can be formed.

Further, by lowering the film forming temperature by this method, an inexpensive substrate can be adopted.

Particularly in the formation of the crystalline silicon film,
The crystallinity of the crystalline silicon film can be improved by applying a mixture having a high catalyst concentration onto the substrate to form a crystal nucleus generation layer, and then applying a mixture having a low catalyst concentration onto the substrate.

If atomic hydrogen gas is supplied to the substrate during thermal decomposition or photolysis, the polymerization can be promoted and the film quality can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an experimental device relating to a method for forming a silicon film of the present invention.

FIG. 2 is a cross-sectional view of a crystalline silicon film

FIG. 3 is a diagram showing a configuration of an experimental device of Example 5.

FIG. 4 is a diagram showing a configuration of an experimental device of Example 6.

FIG. 5 is a diagram showing the configuration of an experimental device of Example 7.

[Explanation of symbols]

1 coating room 2 Film forming chamber 4 High-order silane solution dropping line 5 Catalyst solution dropping line 9 heating heater 12 Low-pressure mercury lamp 13 Hydrogen gas introduction line 14 Microwave generation chamber A substrate B First coating layer C second coating layer

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/208 H01L 31/04 C23C 18/08 C23C 18/14 C01B 33/02

Claims (7)

(57) [Claims] 1. The general formula Si _n H _{2n + 2} (n is an integer of n ≧ 3)
Higher order silane represented by the general formula, or Si _n H _l X _m (X is a salt
One of elemental, fluorine, bromine or iodine, l +
m = 2n + 2, n is a halogen represented by n ≧ 3)
With a solution of high-order silane, nickel, iron, cobalt or
Consist of a substance or solution containing at least one of platinum
A method for forming a silicon film, which comprises thermally decomposing a mixture with a catalyst to form a silicon film on a substrate. 2. The general formula Si _n H _{2n + 2} (n is an integer of n ≧ 3)
Higher order silane represented by the general formula, or Si _n H _l X _m (X is a salt
One of elemental, fluorine, bromine or iodine, l +
m = 2n + 2, n is a halogen represented by n ≧ 3)
With a solution of high-order silane, nickel, iron, cobalt or
Consist of a substance or solution containing at least one of platinum
A method of forming a silicon film, which comprises photo-decomposing a mixture of a catalyst with a catalyst having a wavelength shorter than 400 nm to form a silicon film on a substrate. 3. A mixture of a solution of higher silane and a catalyst is heated.
When decomposing and forming a silicon film on the substrate,
A mixture of high degree is applied to the substrate to form a crystal nucleation layer.
And apply a mixture with a low catalyst concentration on it.
A method for forming a silicon film, comprising: 4. A mixture of a solution of a high order silane and a catalyst
Photolysis by irradiating light with a wavelength shorter than 00 nm
Then, when forming a silicon film on the substrate,
Applying a large mixture onto a substrate to form a crystal nucleation layer
And apply a mixture with a low catalyst concentration on it.
A method for forming a characteristic silicon film. 5. Atomic hydrogen gas on the substrate during thermal decomposition
The system according to claim 1 or 3, characterized in that
Method for forming recon film. 6. Atomic hydrogen gas on the substrate during photolysis
The system according to claim 2 or 4, characterized in that
Method for forming recon film. 7. The solvent of the catalyst is such that the higher order silane is soluble in it.
A solvent that has a boiling point lower than the temperature at which the silicon film is formed
7. The method according to any one of claims 1 to 6, wherein
Method for forming a silicon film.