JPH01172295A - Production of silicon crystalline thin film by epitaxial growth - Google Patents

Abstract

PURPOSE:To reduce energy cost per unit product and to improve production efficiency and product quality and to relax the controlling range of quality of a substrate by utilizing a gaseous mixture consisting of film formable gas such as SiH4, etching gas of prescribed times thereof and gaseous H2 as reactive gas in the case of producing the title thin film. CONSTITUTION:Si atom.-contg. reactive gas at 0.5-10Torr is obtained by mixing (A) SiH2 and/or Si2H6 utilized as film formable gas of a silicon thin film, (B) SiF4 and/or SiF6 utilized as etching gas of 5-100 times for component A and (C) gaseous H2 of 30-300 times for component A while regulating the pressure. Then this reactive gas at 0.5-10Torr is made to plasma by high-frequency of 0.3-2.5W/cm<2> power flux density and the title high-quantity crystalline thin film is subjected to epitaxial growth on a substrate maintained at constant temp. in a range within 100-300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a silicon crystal thin film that can be used for semiconductors such as bipolar transistors, and particularly to a method of manufacturing an epitaxially grown silicon crystal thin film.

(Conventional technology) Conventionally, bipolar transistor, bipolar IC5MO
3. CVD is a common epitaxial growth method in the manufacture of semiconductors such as LSI memories. According to this CVD method, for example, "the latest LSI process technology"
(Written by Kazuo Maeda, Kogyo Kenkyukai, pp. 189-209, 19
As described in 1983), even in the case of the sealed tube method using the 5i-1 system, which allows epitaxial growth of silicon at relatively low temperatures, the crystal growth temperature is 900° C. or higher. In addition, in recent years, in order to lower the crystal growth temperature, 5% has been added to the raw material.
There is a tendency to use materials that decompose at low temperatures, such as izH6, but even in this case it is difficult to keep the growth temperature below 800°C, and when forming a silicon thin film on a substrate by CVD, it is difficult to use materials that contain silicon atoms. It was necessary to set and maintain the reaction gas such as the raw material and the substrate temperature at 800 to 1200°C.

On the other hand, JP-A-58-172217 is an example of forming a silicon thin film using a reactive gas such as a raw material containing silicon atoms and keeping the temperature on the substrate at 800 DEG C. or lower.

However, this invention reduces the temperature of the reaction chamber to 400-900°C.
A polycrystalline silicon film is formed by thermal decomposition CVD from a reaction gas containing a silane compound while maintaining the temperature at 0°C. A large amount of thermal energy is required to heat the reaction gas, which has poor heat transfer efficiency, to the above temperature. In addition, not only does heating and cooling take a considerable amount of time, but epitaxial growth of silicon cannot be realized.

Furthermore, Japanese Patent Application Laid-Open No. 61-65421 proposes a plasma chemical vapor deposition apparatus, and states that this apparatus can normally form a silicon thin film at a substrate temperature of about 500°C. There is. However, the purpose of the invention disclosed in this publication is to reduce the power consumption of the substrate heater, and from the description in the upper right column to lower left column on page 3 of the publication, it is clear that the substrate surface temperature is 500°C, the reaction gas flow rate is 300°C.
Although it is presumed that an amorphous silicon thin film is formed by the above-mentioned proposed apparatus at a vacuum degree of ITorr for cZ, there is no suggestion at all about the possibility of epitaxial growth of silicon.

However, recently, a capacitively coupled RF plasma CVD device was used to perform glow discharge decomposition of a mixed system of SiH and 5iHzFz, and (100)St was decomposed at a low temperature of about 200'C.
It has been found that a Si single crystal with a good surface condition can be grown on a single crystal substrate (1987 Spring Proceedings of the Japan Society of Applied Physics 29a-C-5).

(Problems to be Solved by the Invention) As a result of intensive studies to further develop this excellent method, the present inventors found that since 3iH2Fz gas is a raw material for silicon crystal film formation and has etching properties,
In addition to discovering that it is difficult to control the reaction gas to obtain a high-quality epitaxially grown film, we also discovered that conventional a-3
The inventors have discovered that very good results can be obtained by diluting the mixed system of SiH and SiF4 used to form the i:H film with a large amount of hydrogen, and have arrived at the present invention.

Therefore, a first object of the present invention is to provide a method for obtaining a high quality silicon single crystal film by performing epitaxial growth at a low substrate temperature of 300° C. or lower.

A second object of the present invention is to provide a method for epitaxially growing silicon at low temperatures while controlling the formation and etching of the silicon film.

(Means for Solving the Problems) The above-mentioned aspects of the present invention provide a method for epitaxially growing silicon on a heated substrate by turning a reactive gas containing a raw material having silicon atoms into plasma using a plasma CVD apparatus. The reaction gas is 5fH4 and/or S 1 z as a film-forming gas for silicon thin film.
About 0.5-10 Hb, 5iFa and/or 5izF6 as etching gas and hydrogen gas mixed
Using a mixed gas at a pressure of Torr, the amount of hydrogen gas is about 30 to 300 times the amount of the film-forming gas, and the amount of the etching gas is about 5 times the amount of the film-forming gas.
~100 times as high, the reaction gas was supplied into the reaction chamber, plasma was generated by high frequency power with a power density of about 0.3 to 2.5 W/cfll, and the temperature was maintained at a constant temperature of about 100 to 300°C. SiH and/or 5i2H as a film-forming gas used in the present invention is a raw material gas for forming a silicon film. It is. However, even with this raw material, it is not possible to grow silicon epitaxially using conventional methods, and in order to achieve epitaxial growth,
It is necessary to meet the special film forming conditions shown in the present invention.

On the other hand, S iFa and/or 5i2 used in the present invention
F is an etching gas that releases fluorine atoms capable of etching silicon under plasma conditions, and forms silicon crystals based on the film-forming gas while keeping the substrate surface always clean through etching. This is the most important feature of the present invention. That is, the fluorine atoms in the plasma are considered to have the following functions: (1) removing impurities from the grown film, (2) removing hydrogen from the grown film, and (2) preventing polymerization of silane in the gas phase. In order to perform epitaxial growth of silicon while balancing film formation and etching by utilizing the function of fluorine atoms, in the present invention, the etching gas is used at a concentration of about 5 to 100% of the film forming gas.
The hydrogen gas is used as a diluent gas about 30 to 300 times as much as the film-forming gas. As described above, it is a major feature of the present invention that the etching gas and hydrogen gas are used in larger amounts than the film forming gas. If the etching gas is less than 5 times the film-forming gas, the substrate surface cannot always be kept in the best condition to facilitate epitaxial growth of silicon, while if it is 100 times or more, the etching rate will decrease. It becomes too large to grow an epitaxial thin film. Furthermore, if the hydrogen gas is less than 30 times the film-forming gas, the movement of film-forming Si atoms, which will be described later, on the substrate surface will be insufficient, making it difficult to perform epitaxial growth, while if the hydrogen gas is 300 times or more,
This is not preferable because the concentration of silicon atoms becomes too low and the formation rate of the epitaxial thin film becomes too slow.

In the present invention, approximately 0.5T that satisfies the above conditions is used.
The reaction gas at a pressure of o r r ~10 Tor r,
A silicon crystal thin film is formed on a substrate maintained at a constant temperature of about 100° C. to 300° C. by turning it into plasma using a high frequency wave with a power density of about 0.3 to 2.5 W/CI+1.

(Function) With the above configuration, the substrate surface always adsorbs hydrogen and can be covered with hydrogen. When a film-forming precursor (SiH, etc.) flies onto the substrate surface covered with hydrogen in this manner, the precursor cannot immediately adhere to the substrate surface but moves along the substrate surface. Precursors that are able to move sufficiently across the surface settle on the energetically most stable sites, thus forming a crystal structure. Furthermore, since the rate of etching with fluorine gas is higher for amorphous silicon than for crystalline silicon, even if amorphous silicon is deposited on the substrate, it is quickly removed and only crystalline silicon is deposited. Moreover, as mentioned above, as a result of sufficient surface movement of the film-forming precursor,
Silicon eventually grows epitaxially on the substrate because it gradually settles on the most stable sites.

As mentioned above, in order to cause the film-forming precursor to move on the surface and realize epitaxial growth of silicon, it is necessary to maintain the substrate temperature between about 100° C. and 300° C. If the substrate temperature is lower than 100°C, the epitaxial growth rate will be extremely slow, which is not practical. When the substrate temperature is higher than 300°C, the quality of epitaxial growth deteriorates because hydrogen adsorption on the substrate surface becomes insufficient.

In addition, the power density and pressure of the reactant gas for generating the plasma affect the kinetic energy of atoms and ions arriving at the substrate, and therefore the quality of epitaxial growth.

Power density is 0. 3W/cil! In the following, since the pressure of the reaction gas must be sufficiently lowered, it is not preferable that the film formation rate is slow<2.5 W/CI+1 or more, since the quality of epitaxial growth cannot be maintained at a high level.

If the pressure of the reaction gas is less than 0.5 Torr, the epitaxial growth rate will be slow, and if it is more than IQTorr, the discharge state will not be stable, which is not preferable.

The method of the present invention can be applied to all fields where epitaxial growth has conventionally been performed, such as semiconductor devices such as pibolar transistors, bipolar TCs, MOSs, and LSI memories, as well as the production of solar cells. .

(Effects of the invention) In the present invention, silicon is epitaxially grown on a low-temperature substrate with low power, so not only can the energy cost per product be lowered, but the time required for heating and cooling the substrate can also be significantly reduced. This increases production efficiency and reduces product costs.

Further, since the thermal distortion that the substrate receives is small, it is also possible to ease the quality control of the substrate used.

(Examples) The present invention will be described in more detail below according to Examples, but the present invention is not limited thereto.

Example 1 5iHa:5iFa:Hz = 1:30:12 was placed in a reaction chamber that had been made to have a high vacuum of 1X10-'' Torr in advance.
0 mixed gas was supplied as a reaction gas at 11005 CC, and the pressure of the reaction gas was adjusted to 2.5 Torr. Next, this reaction gas was heated using a 13.56MH2 high frequency power source.
Power density1. 31 W/c+fl to plasma, 2
(a) 500 people, (
b) A silicon crystal thin film was formed to a thickness of 2,000 and (c) 1.6 μm.

The silicon crystal thin films of each of the samples (a), (b), and (c) obtained as described above were evaluated by reflection high-energy electron diffraction (RHEED). It turned out to be a crystal (Figures 1 to 3)
. This proves that epitaxial growth of silicon was performed by the method of the present invention.

Example 2 The Raman half-width of the films obtained by changing the ratio of SiF</SiH under the film forming conditions of Example 1 was measured. The dependence of the Raman half-width on S i F a /SiH is shown in FIG.
It is clear that particularly good results are obtained with a ratio of iF, /SiH, of about 5 to 100.

Example 3 The Raman half-width of a film obtained by changing the substrate temperature under the film forming conditions of Example 1 was measured.

The dependence of the Raman half-value width on the substrate temperature is shown in Figure 5, and under these film forming conditions, the substrate temperature is approximately 100 to 3
It is clear that good results are obtained at 00°C.

Example 4 The Raman half-width of the films obtained by changing the power density under the film forming conditions of Example 1 was measured.

The power density dependence of the Raman half-width is as shown in Figure 6, and under these film forming conditions, the power density is approximately 0.3 to 2.
．． It is clear that good results are obtained with 5 W/cm''.

Example 5 The H2/SiH4 ratio under the film forming conditions of Example 1 was varied. In this case, the dependence of the film formation rate on H2/SiH is linear, as shown in Figure 7, and it is clear that when H,/SiH4 exceeds 300, the film formation rate becomes too slow to be practical. .

It should be noted that if H,/SiH, is less than 30, not only epitaxial growth but also amorphous silicon starts to be deposited, which is not preferable.

Example 6 The pressure of the reaction gas under the film forming conditions of Example 1 was varied. The pressure dependence of the film formation rate in this case is as shown in FIG. 8, and it is clear that if the pressure is less than 0.5 Torr, the film formation rate is too slow to be practical. Pressure is 10To
If it exceeds r, the discharge will not be stable, which is not preferable.

Example 7 In order to measure the electrical characteristics of a silicon epitaxial thin film obtained by the method of the present invention, a Schottky diode shown in FIG. 9 was fabricated.

The substrate is N type with a resistivity of 0.0015Ω/c.
A non-doped epitaxial thin film with a thickness of 10 μm was formed under the same conditions as in Example 1 using a va low resistance silicon substrate.

As shown in Fig. 10, the rectification characteristics of the obtained diode are such that the forward current rises steeply, and the n value is approximately 1.1.
Met. Furthermore, the rectification ratio at an applied voltage of 0.5 V was greater than 6 orders of magnitude. These characteristics closely match those of an ideal crystalline silicon Schottky diode, and demonstrate that the quality of the epitaxial thin film grown by the present invention is extremely good.

Example 8 Using the Schottky diode obtained in Example 2, c
When the defect density Nd in the epitaxial thin film was measured by the '-v method, it was verified that the defect density Nd was approximately 5 x 10'' pieces/C-, which was extremely good.

[Brief explanation of the drawing]

1 to 3 are RHEED diffraction diagrams of the epitaxial film produced in Example 1. FIG. 1 shows the case where the film thickness is 500, FIG. 2 shows the case where the film thickness is 2000, and FIG. 3 shows the case where the film thickness is 1.6 μm. Figure 4 shows Raman half-width and S i Fa / S i
) (This is a graph showing the relationship between the ratio of 4. Figure 5 is a graph showing the relationship between the Raman half-width and the substrate temperature. Figure 6 is a graph showing the relationship between the Raman half-width and the power density during discharge. FIG. 7 is a graph showing the dependence of the film formation rate on H,/5iHa. FIG. 8 is a graph showing the dependence of the film formation rate on reaction gas pressure. 10 is a conceptual diagram of a Schottky diode manufactured in Example 2. In the figure, reference numeral 1 represents a substrate, 2 represents an epitaxial film, 3 represents an indium electrode, and 4 represents a gold electrode. The rectification characteristics of the fabricated epitaxial film are shown. In the figure, the symbol * indicates the case where the voltage is applied in the forward direction, and the symbol O indicates the case where the voltage is applied in the reverse direction. Patent applicant: Toa Fuel Industries Co., Ltd.

Claims (1)

[Claims] (1) In a method of epitaxially growing silicon on a heated substrate by turning a reactive gas containing a raw material containing silicon atoms into plasma using a plasma CVD apparatus, the reactive gas is SiH_4 as a film-forming gas for a silicon thin film. and/or Si_2H_6, SiF_4 and/or Si_2F_6 as an etching gas, and hydrogen gas at a pressure of about 0.5-10 Torr, and the amount of hydrogen gas is adjusted to the amount of the film-forming gas. At the same time, the amount of the etching gas is set to be about 5 to 100 times the amount of the film forming gas, and the reaction gas is supplied into the reaction chamber to achieve a power density of about 0.3.
A method for producing a silicon thin film by epitaxial growth, characterized by generating plasma using a high frequency of ~2.5 W/cm^2 and forming a silicon crystal thin film on a substrate maintained at a constant temperature between about 100 and 300°C. .