JPH06204139A - Manufacture of silicon crystal film by thermal cvd - Google Patents

Abstract

PURPOSE:To manufacture a high quality silicon crystal film at a temperature lower than the conventional case, without using a film forming equipment applying high vacuum. CONSTITUTION:Film forming gas composed of SiH4 and SiF4 gas which is hard to be thermally decomposed are supplied to the inside of a film forming chamber 11 set in the state of vacuum at about 1X10<-5>Torr, and an epitaxial silicon thin film is continuously formed on a silicon single crystal substrate 14 heated at 700 deg.C. Since the SiF4 gas reacts with radical component of thermally decomposed SiH4, and the thermal decomposition is accelerated, high density fluorine based radicals locally exist in the region in the vicinity of the substrate where many SiH4 radical components are present. Hence impurities mixed in a substrate or a growing silicon film are eliminated by the etching action of the fluorine based radicals, so that the substrate heating temperature can be lowered. On the other hand, since SiF4 is hard to be thermally decomposed, the concentration of the fluorine based radicals in the film forming chamber is low, so that generation of floating foreign matter caused by corrosion action of the fluorine based radicals can be restrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon crystal film used in a thin film transistor, a solar cell or the like, and more particularly, to a high-quality silicon under a lower temperature condition than before without applying a high vacuum film forming apparatus. Thermal CV capable of forming crystalline film
The present invention relates to a method for producing a silicon crystal film by D.

[0002]

2. Description of the Related Art As a method for producing a silicon crystal film by a thermal CVD method, a method described in Japanese Patent Laid-Open No. 172217/58 is known.

That is, in this manufacturing method, a film-forming gas made of a silane compound is supplied into a film-forming chamber in which a substrate is arranged,
This is a method of thermally decomposing this film-forming gas near the heated substrate to form a silicon crystal film on this substrate.

By the way, in this method, in order to prevent impurities contained in the film-forming gas and impurities generated by thermal decomposition of the film-forming gas from entering the silicon crystal film, It is necessary to heat the substrate to a temperature of 900 ° C. or higher to thermally decompose and remove the impurities mixed in the substrate or the growing silicon film, and there is a drawback that a large amount of thermal energy is required for heating the substrate. It was

On the other hand, a method has been proposed in which the degree of vacuum in the film forming chamber is increased before the film formation is started to remove impurities in the film forming chamber as much as possible to reduce the heat energy to be input. In carrying out this method, since an expensive film forming apparatus capable of setting a high vacuum in the film forming chamber is required, there is a disadvantage in that the manufacturing cost of the silicon crystal film becomes high accordingly.

Therefore, recently, a plasma CVD method capable of producing a silicon crystal film under a low temperature condition has been attracting attention (for example, Japanese Patent Laid-Open Nos. 63-157872 and 63-63).
175417). That is, the methods disclosed in these publications supply a source gas containing a silicon atom, a halogen atom, and a hydrogen atom into the film forming chamber,
In addition, this source gas is made into plasma and reacted on the substrate to form a silicon crystal film, and the impurities mixed in the substrate or the growing silicon film by the etching action of the halogen atoms turned into plasma are Since it was removed, it was a method that enables film formation under low temperature conditions as compared with the thermal CVD method.

[0007]

However, in this plasma CVD method, low temperature film formation is possible as described above, but on the other hand, a large amount of powdery suspended foreign matter is likely to occur in the film formation chamber during the film formation process. However, there is a drawback that the floating foreign matter is mixed into the silicon crystal film during film formation and deteriorates the film characteristics.

That is, in this plasma CVD method, the plasma-formed raw material gas is uniformly distributed in the plasma forming region in the film forming chamber, and the plasma-converted raw material gas is in an excited state. The raw material gases react with each other in an arbitrary space to generate a powdery substance of silicon, or the raw material gas that has been turned into plasma reacts on a portion other than the substrate, that is, the inner wall surface of the film forming chamber, and silicon is deposited to form a powdery substance. A large amount of powder-like floating foreign matter that is peeled off as a body is likely to be generated, and the inner wall surface of the film forming chamber and the inner jig surface are easily corroded by the etching action of the halogen atoms. It peels off and joins the floating foreign matter.

As described above, although low temperature film formation is possible in the plasma CVD method, a large amount of powdery suspended foreign matter is likely to be generated in the film formation chamber during the film formation process, which is generated in the growing silicon crystal film. There is a defect that the film characteristics are deteriorated by being mixed, and there is a problem that it is difficult to manufacture a high-quality silicon crystal film by the plasma CVD method.

Further, in this plasma CVD method, an expensive film forming apparatus equipped with a plasma forming means is required for carrying out the plasma CVD method. Therefore, like the above-mentioned thermal CVD method using a high vacuum film forming apparatus, a silicon crystal film is formed. There was a problem that the manufacturing cost of was expensive.

The present invention has been made by paying attention to such a problem, and its object is to prevent the inclusion of floating foreign matters under a lower temperature condition than before without applying a high vacuum film forming apparatus. Thermal CVD that can produce high quality silicon crystal film
Another object of the present invention is to provide a method for manufacturing a silicon crystal film according to.

[0012]

Under such a technical background, the present inventor pays attention to the etching action of halogen atoms in the plasma CVD method, and SiF ₄ which is hardly decomposed by the film-forming gas such as silane compound. Thermal CV mixed with gas
When an attempt was made to improve the D method, this SiF ₄ gas was unexpectedly promoted by the reaction with the radical components of the thermally decomposed film-forming gas, and the fluorine-based radicals produced by this decomposition were etched. It was found that the substrate heating temperature can be reduced by the action, and the present invention has been completed.

That is, according to the first aspect of the invention, a film-forming gas containing silicon atoms is supplied into the film-forming chamber in which the substrate is arranged, and the film-forming gas is thermally decomposed in the vicinity of the heated substrate to form the film-forming gas. Thermal CV for forming a silicon crystal film on a substrate
Based on the method for producing a silicon crystal film by D, SiF ₄ gas is mixed with the above film-forming gas, and a fluorine-based radical generated by the reaction between the radical component of the thermally decomposed film-forming gas and the above SiF ₄ gas is added. It is characterized in that a silicon crystal film is formed on the substrate while acting as an etching component.

In the invention according to the first aspect, since SiF ₄ gas, which is hard to undergo thermal decomposition, is used as the gas for releasing the halogen atom, the amount of fluorine in the film forming chamber that is difficult to thermally decompose is used. The system radical concentration is low.

Therefore, as compared with the plasma CVD method, the film-forming gas reacts with the fluorine-based radicals to generate silicon powder in an arbitrary space in the film-forming chamber, or the inner wall surface of the film-forming chamber or Since the surface of the inner jig is less likely to be corroded by the action of the above-mentioned fluorine-based radicals, the generation of floating foreign matter in the film forming chamber is prevented despite the use of SiF ₄ gas that releases halogen atoms. It becomes possible to do.

On the other hand, while the SiF ₄ gas is less susceptible to thermal decomposition, its thermal decomposition is accelerated by the reaction with the radical components of the thermally decomposed film-forming gas such as a silane compound.
In the region where the radical component is large, that is, in the region near the substrate, the fluorine-containing radicals of high concentration are unevenly distributed in this region.

Therefore, only the impurities mixed in the silicon film on the substrate or during the growth are selectively removed by etching, so that the substrate is correspondingly removed without applying a high vacuum film forming apparatus. The heating temperature can be reduced.

Incidentally, in the thermal CVD method, in order to maintain the vacuum degree in the film forming chamber substantially constant during the film forming process, the exhaust process is continuously performed on the downstream side of the film forming process, which is used for the etching action. Fluorine-based radicals or surplus fluorine-based radicals are removed from the film forming chamber to the outside by the exhaust treatment.

In such a technical means, the film-forming gas containing silicon atoms is easily decomposed by S.
iH ₄ , Si ₂ H ₆ , Si ₃ H _{8 and} other silicon hydrides and SiH _m
X _4-m (where m is 1 to 3, preferably 2 to 3, X is C
1 or an F atom, preferably an F atom), or the like. Incidentally, hydrogen gas may be added to the film forming gas. This hydrogen-based radical also acts on the SiF ₄ gas to promote its decomposition.

Here, when the latter halogenated silane gas is applied as the film-forming gas, the above-mentioned floating foreign matter may occur in the film-forming chamber if the mixing ratio of the halogenated silane gas is too high. Therefore, when the halogenated silane gas represented by SiH _m X _4-m is applied, it is desirable to set the compounding ratio thereof to be smaller than that of SiF ₄ .

Further, as a diluent gas in the film forming gas,
You may add inert gas, such as helium, neon, and argon.

Then, the mixing ratio of the above-mentioned film forming gas such as silicon hydride and the SiF ₄ gas is 1: 5 to 10 by volume ratio.
The raw material gas is mixed with the above-mentioned hydrogen gas or inert gas, etc., if necessary, and introduced into the film forming chamber, and is thermally decomposed in the vicinity of the heated substrate to cause silicon crystals on the substrate. It is a method of forming a film.

Any heat resistant material can be applied to the substrate. For example, when a silicon single crystal substrate is applied, a silicon single crystal film is required, and a glass substrate,
When a substrate other than a silicon single crystal substrate such as a ceramic substrate, a metal substrate, or a carbon-based substrate is applied, a silicon polycrystalline film is required.

As described above, in the present invention, the degree of vacuum in the film forming chamber before the start of film forming is set to such a degree that some impurities remain in the film forming chamber (about 10 ^-5 Torr), and the substrate is heated. Even if the temperature is set to a low temperature of about 700 ° C., the impurities are selectively removed by the etching action of the fluorine-based radicals, and the generation of floating foreign matter hardly occurs, so that the impurities are not easily mixed into the silicon film. Therefore, there is almost no possibility of adversely affecting the film characteristics of the silicon crystal film.

Therefore, there is an advantage that a high-quality silicon crystal film can be manufactured under a lower temperature condition than before without applying an expensive film forming apparatus capable of setting a high vacuum.

[0026]

According to the invention of claim 1, SiF ₄ gas is mixed with the film-forming gas containing silicon atoms, and
The present invention is characterized in that a silicon crystal film is formed on a substrate while a fluorine-based radical generated by the reaction of the thermally decomposed radical component of the film forming gas and the SiF ₄ gas is used as an etching component.

SiF ₄ gas, which is not easily decomposed by heat, is used as the gas for releasing halogen atoms, and the fluorine-containing radical concentration in the film forming chamber is low because the gas is hardly decomposed by heat. Therefore, as compared with the above-mentioned plasma CVD method, the film-forming gas reacts with a fluorine-based radical to generate a silicon powder in an arbitrary space in the film-forming chamber, or the inner wall surface of the film-forming chamber or the inner jig surface. Is extremely unlikely to be corroded by the action of the above-mentioned fluorine-based radicals, and it is possible to reliably prevent the generation of floating foreign matter in the film forming chamber, even though SiF ₄ gas that releases halogen atoms is used. It becomes possible to do.

Further, the above-mentioned SiF ₄ gas is accelerated in its thermal decomposition by the reaction with the radical components (SiH _x radicals, H-based radicals, etc.) of the film-forming gas. Since the fluorine-based radicals are easily unevenly distributed, it is possible to selectively etch only the impurities mixed in the silicon film on the substrate or during growth, and the substrate can be correspondingly etched without applying a high-vacuum film forming apparatus. It is possible to reduce the heating temperature.

[0029]

EXAMPLES Examples of the present invention will now be described in detail, but the present invention is not limited to these examples.

FIG. 1 is an explanatory view showing a schematic structure of a thermal CVD apparatus applied in the embodiment. In the figure, 11 is a closed film forming chamber, 13 is a substrate holder in which a heater 15 is incorporated,
14 is a substrate attached to the substrate holder 13, 1
6 and 17 are supply sources of raw material gas, and 18 is a pressure regulating valve 19
The decompression pumps connected to the film forming chamber 11 via the respective are shown.

[Embodiment 1] A mixed gas of SiH ₄ and SiF ₄ (a gas ratio of SiH ₄ : SiF ₄ = 1 in volume ratio) was set in a film forming chamber 11 which had been previously evacuated to 1 × 10 ^-5 Torr. : 10
Is supplied as a source gas at 80 SCCM, and an epitaxial silicon thin film is continuously formed on a silicon single crystal substrate heated to 700 ° C. in a state where the pressure of the source gas is adjusted to 0.1 Torr, An epitaxial silicon thin film having a film thickness of 1 μm was manufactured.

Raman spectroscopic analysis was carried out on the obtained thin film, and the half width at the position of 520 cm ^-1 was 3.
A very sharp spectrum based on crystalline silicon at 5 cm ^-1 was observed.

Further, when the defect density in the obtained epitaxial silicon thin film was measured, it showed a value of about 10 ⁵ to 10 ⁶ (/ cm ² ) at which the crystallinity was evaluated as good, and impurities were extremely mixed. There were few.

Furthermore, reflection high-energy electron diffraction (RHEED)
When the silicon crystal thin film was evaluated by, a streak pattern and a Kikuchi line were observed, and it was confirmed that the film was a good single crystal.

The specific resistance of this thin film was 0.1 to 1 Ω · cm, and the electron mobility was determined to be 600 cm ² / V · S by a Hall effect measuring device applying the van der Apo method.
Met.

[Embodiment 2] SiH ₄ , SiF ₄ , and SiF ₄ were placed in the film forming chamber 11 which was previously evacuated to 1 × 10 ^-5 Torr.
Mixed gas of H ₂ (gas ratio is SiH ₄ : Si in volume ratio)
F ₄ : H ₂ = 1: 10: 1) as source gas
Supply at 0 SCCM and set the source gas pressure to 0.1T
A silicon polycrystalline film is continuously formed on a glass substrate heated to 700 ° C. in a state adjusted to orr, and the film thickness is 1 μm.
Was manufactured.

As a comparative example, when a similar silicon polycrystal film was manufactured by the plasma CVD method, the film characteristics of the silicon polycrystal film according to the example were remarkably excellent.

[0038]

According to the first aspect of the present invention, SiF ₄ gas, which is less susceptible to thermal decomposition, is used as the gas that releases halogen atoms. Since the system radical concentration is low, the film-forming gas reacts with the fluorine-based radicals to form a silicon powder in an arbitrary space in the film-forming chamber as compared with the above-mentioned plasma CVD method. It is extremely unlikely that the inner wall surface of the film chamber or the inner jig surface is corroded by the action of the above-mentioned fluorine-based radicals, and the film is formed despite the use of SiF ₄ gas that releases halogen atoms. It is possible to reliably prevent the generation of floating foreign matter in the room.

Further, since the SiF ₄ gas is accelerated in its thermal decomposition due to the reaction with the radical components (SiH _x radicals, H-based radicals, etc.) of the film-forming gas, it is highly concentrated in the region near the substrate where the radical components are large. Since the fluorine-based radicals are easily unevenly distributed, it is possible to selectively etch only the impurities mixed in the silicon film on the substrate or during growth, and the substrate can be correspondingly etched without applying a high-vacuum film forming apparatus. It is possible to reduce the heating temperature.

Therefore, there is an effect that a high-quality silicon crystal film free from inclusion of floating foreign matters can be produced under a lower temperature condition than before without applying a high-vacuum thermal CVD apparatus.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view of a thermal CVD apparatus applied in an example.

[Explanation of symbols]

 11 film forming chamber 13 substrate holder 14 substrate 15 heater 16 source gas supply source 17 source gas supply source 18 pressure reducing pump 19 pressure regulating valve

Claims (1)

[Claims] 1. A film forming gas containing silicon atoms is supplied into a film forming chamber in which a substrate is arranged, and the film forming gas is thermally decomposed in the vicinity of the heated substrate to form a silicon crystal film on the substrate. In a method for producing a silicon crystal film by thermal CVD for film formation, a SiF ₄ gas is mixed with the above film-forming gas, and a fluorine-based radical generated by a reaction between a radical component of the thermally decomposed film-forming gas and the SiF ₄ gas. A method for producing a silicon crystal film by thermal CVD, which comprises forming a silicon crystal film on the substrate while acting as an etching component.