JPH0277116A - Manufacture of silicon crystal thin film - Google Patents

Abstract

PURPOSE:To obtain a single crystal thin film of silicon which has substantially no transition region by generating plasma by supplying reactive gas to a reaction chamber, in the manner in which the amount of etching gas becomes about 0.1-50 times the amount of film forming gas, and forming the silicon crystal thin film on a substrate kept at a constant temperature between about 100-700 deg.C. CONSTITUTION:Silane or disilane is preferable for film forming gas. Fluorine gas to be used is a gas with intense etching property, and the substrate surface is kept always clean by etching. In order to epitaxially grow silicon while film forming and etching are balanced by utilizing the function of fluorine atom, the fluorine gas is set as about 0.1-50 times, or desirably 0.5-30 times the film forming gas. The above reactive gas at a pressure of about 0.1-15Torr is made plasma by high frequency discharge whose power density is about 0.1-5W/cm<2>, thereby forming a crystal thin film of silicon on a substrate kept at a constant temperature between about 100 deg.C and 700 deg.C.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a silicon crystal thin film, and in particular to a method for manufacturing a silicon crystal thin film using fluorine gas as an etching gas.
The present invention relates to a method for manufacturing a 1i film.

(Prior art) Conventionally, bipolar transistor, bipolar IC, MO
CVD is a common epitaxial growth method for manufacturing semiconductors such as 5SLS1 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), 5i-1! enables epitaxial growth of silicon at relatively low temperatures. Even in the case of the sealed tube method using the system, the crystal growth temperature is over 900''C.In recent years, in order to lower the crystal growth temperature, materials that decompose at low temperatures such as Si!H, etc. have been used as raw materials. However, 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 the CVD method, the reaction gas such as the raw material containing silicon atoms and the substrate temperature It was necessary to set and maintain the temperature between 800 and 1200'C.

Furthermore, Japanese Patent Application Laid-Open No. 61-65421 proposes a plasma chemical vapor deposition apparatus, and it is stated that this apparatus can normally form a silicon thin film at a substrate temperature of about 500°C. ing. However, the invention disclosed in this publication is aimed at reducing the power consumption of the substrate heater, and there is no suggestion at all about the possibility of epitaxial growth of silicon.

Under these circumstances, we have recently performed glow discharge decomposition of a mixed system of 5tH4 and 5iHtFz using a capacitively coupled RF plasma CVD device, and have developed a method for decomposing (100) at a low temperature of approximately 250°C.
It has been discovered that it is possible to grow Si single crystals with good surface conditions on Si single crystal plates (Japanese Journal of Applied Physics, 26).
Volumes, L951-L953 (1987)).

While considering further development of this excellent method, the present inventors discovered that 5iHzFz gas is a raw material for silicon crystal film formation, and at the same time has etching properties. It was discovered that it was difficult to control the gas, making it difficult to produce thin films with good crystal quality.
It was discovered that very good results could be obtained by diluting the mixed system of S i H4 and S i Fa used for film formation with a large amount of hydrogen, and the patent ratio 1jJl was first performed.

On the other hand, with regard to polycrystalline silicon, recent research has shown that polycrystalline silicon produced by the thermal CVL method has many gaps between silicon particles due to the high temperature during production, and the crystals do not adhere to each other. It has been found that dangling bonds at grain boundaries deteriorate electrical characteristics, and it has also come to be known that grain boundaries must be passivated with hydrogen to correct this disadvantage.

For this reason, the plasma CVD method, which can produce polycrystalline silicon thin films at low temperatures, has recently attracted attention (see JP-A-63-157872 and JP-A-63-175417).
. These methods have the advantage that the polycrystalline silicon obtained contains hydrogen between silicon particles compared to the thermal CVD method, and there is no need to passivate the polycrystalline silicon that has been produced afterward. The polycrystalline silicon thin film obtained contained hydrogen in an amount of about 2.5 atomic % or more, and there was room for further improvement in terms of the performance of the polycrystalline silicon thin film.

(Problems to be Solved by the Invention) As a result of intensive studies to solve these drawbacks, the inventor of the present invention found that when fluorine gas is used as an etching gas, during plasma generation for growing a silicon crystal thin film, Plasma conditions such as high-frequency power can be matched only to 5iHn, which is the film-forming gas source, and this can further improve the performance of epitaxial thin films obtained when using silicon sentry crystal substrates. The inventors have discovered that when a substrate other than a crystalline substrate is used, a polycrystalline silicon thin film of higher quality than before can be obtained, and the present invention has been achieved.

Therefore, a first object of the present invention is to provide a method for epitaxially growing on a silicon single crystal substrate at a low substrate temperature of 700° C. or lower to obtain a high quality silicon wheel crystal film.

A second object of the present invention is to provide a method for forming a high-quality polycrystalline silicon thin film on a substrate other than silicon single crystal at a low substrate temperature of 700'C or less.

(Means for Solving the Problems) The above-mentioned aspects of the present invention provide a method for growing a silicon crystal thin film on a heated substrate by converting a reactive gas containing a raw material having silicon atoms into plasma using a plasma CVD method. The reaction gas is a mixed gas consisting of at least silicon hydride as a film-forming gas and fluorine gas as an etching gas diluted with an inert gas, and the amount of the etching gas is less than the amount of the film-forming gas. Approximately 0.1-50
A silicon crystal thin film is formed on a substrate maintained at a constant temperature between about 100 and 700''C by supplying the reaction gas into a reaction chamber so as to generate plasma. This was achieved by a thin film manufacturing method.

The present invention will be explained in more detail below.

Silicon hydride used as a film-forming gas in the present invention is a raw material gas for forming a silicon thin film, and is specifically represented by Si, H, i, z (n''1 to 4). In the present invention, silane or disilane is particularly preferred among these.

On the other hand, the fluorine gas used in the present invention is a strong etching gas, and the etching process keeps the substrate surface clean at all times, and the plasma conditions are optimal for the film-forming gas when forming silicon crystals. This is the most important feature of the present invention. That is, fluorine atoms in the plasma are considered to have the functions of (1) removing impurities in 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 such functions of fluorine atoms, in the present invention, the fluorine gas is used at a concentration of about 0.0% of the film forming gas. 1 to 50 times, preferably 0
．． 5 to 30 times. Additionally, hydrogen gas can be used as the diluent gas.

In this case, the amount of hydrogen gas used is approximately 50% of the film forming gas.
It is preferably 0 times (capacity ratio) or less, particularly 300 times or less. If the amount of hydrogen gas is 500 times or more that of the film-forming gas, the concentration of silicon atoms becomes too low and the growth rate of the silicon crystal thin film becomes too slow.

Furthermore, since fluorine gas is extremely active, it is used after being diluted with an inert gas such as He or Ar in order to prevent corrosion of the equipment. Fluorine gas is about 0.0% of the film-forming gas. 1
It is preferable to increase the capacity by 50 times to 50 times (capacity ratio). Fluorine gas is a film-forming gas of 0. If it is less than 1x, the substrate surface cannot always be kept in the best condition to facilitate the growth of silicon crystals, while if it is more than 50x -F, the etching rate becomes too high and the growth rate of the silicon crystal thin film is reduced. decreases. It is preferable to use the inert gas in an amount of 1 to 15,000 times, particularly 5 to 100 times, the amount of fluorine gas. In addition, known substances such as phosphorus and boron can be added as dopants to the reaction gas, and as the dopant to be used, a compound from Group I of the Periodic Table of Elements or a compound from Group V of the Periodic Table of Elements is selected. Depending on the method, a P-type or N-type silicon crystal thin film can be obtained.

In the present invention, about 00lTo which satisfies the above conditions is used.
The reaction gas at a pressure of r rxl 5'r'o r r is turned into plasma by, for example, a high frequency discharge with a power density of about 061 to 5 W/cd, and the reaction gas is turned into plasma at a pressure of about io o'c to 700°C.
A silicon crystal thin film is formed on a substrate maintained at a constant temperature between 1 and 2. When a silicon single crystal substrate is used as the substrate, a silicon crystal thin film is epitaxially grown to obtain a silicon single crystal thin film. On the other hand, if a substrate other than single crystal silicon is used, for example, a substrate other than single crystal silicon such as glass, ceramic, or metal, although it is not possible to obtain a silicon single crystal thin film, the electron mobility is
~30 cd/volt-second and the hydrogen concentration in the film is 0.
A polycrystalline silicon thin film of extremely high quality of about 1 to 2.0 atomic % can be obtained.

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 immediately removed and only crystalline silicon is deposited.

As mentioned above, in order to obtain a silicon single crystal thin film or a high quality polycrystalline silicon thin film, the substrate temperature should be set at about 100°C to 7°C.
It is necessary to maintain the temperature between 00°C, especially between 200°C and 500°C.
1. If the plate temperature is lower than 100°C, the silicon crystal growth rate will be extremely slow, which is not practical. When the substrate temperature is higher than 700° C., the quality of the obtained crystal deteriorates.

Furthermore, the power density and the pressure of the reactant gas for generating plasma affect the kinetic energy of atoms and ions arriving at the substrate, and therefore the quality of the silicon crystals formed.

Power density is 0. Below IW/cd, the decomposition energy of the reaction gas is insufficient, so the biofilm speed is slow, and 5W/c-
This is not preferable because the damage caused by ionic molecules and atoms becomes large and the quality of the silicon crystal thin film cannot be maintained at a high level.

If the pressure of the reaction gas is less than 0.1 Torr, the silicon crystal growth rate will be slow, and if it is more than 15 Torr, the discharge state will not be stable, which is not preferable.

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

(Effects of the Invention) In the present invention, silicon can be epitaxially grown on a low-temperature substrate with low power, so impurities contained in the substrate can be suppressed from diffusing into the silicon crystal, and therefore substantially A silicon single crystal thin film without a transition region can be obtained. Furthermore, not only can the energy cost per product be lowered, but also the time spent heating and cooling the substrate can be significantly shortened, so production efficiency can be increased and product costs can be lowered.

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

Example 1゜SiH4:Fz:l(!:He-1:10:
1003CC with 100:80 mixed gas as reaction gas
The pressure of the reaction gas was adjusted to 2.0 Torr. Next, this reaction gas was turned into plasma at a power density of 1°3LW/ctA using a 13°56MH2 high frequency power source, and was placed on a silicon single crystal substrate heated to 200'C.
A silicon crystal thin film was formed to a thickness of μm.

When the silicon crystal thin film of the sample obtained as described above was evaluated by reflection high-speed electron diffraction (RH MiF, D), it was found to be a good single crystal. This is to demonstrate that epitaxial growth of silicon was performed by the method of the invention.

The electron mobility of the obtained gi film was determined using a Hall effect simulation device applying the Betritz method and was found to be 1°100c4.
/ volt-second, which was confirmed to be extremely good.

Comparative example 1゜ SiH was used instead of the reaction gas used in Example 1.

, SiH! A mixed gas of F and H2 is used as a reaction gas, and each component gas is ISCCM, 5SCCM and 11005, respectively.
A silicon thin film was produced in the same manner as in Example 1, except that the total pressure of the reaction gas was ITorr, and the high frequency power density was IW/c+If. When the film was evaluated by RHEED, epitaxial growth was confirmed in the case of 1,500 thin films, but only a ring pattern and some spots were observed in the case of 3,000 films, indicating that it was not suitable for amorphous silicon and polycrystalline silicon. It turned out that it was.

Example 2゜F! under the film forming conditions of Example 1! The Raman half-width of the films obtained by changing the ratio of /5iHn was measured.

The dependence of the Raman half-width on Ft/SiH is shown in Figure 1, and it is clear that under these film formation conditions, particularly good results can be obtained with a Fg/SiH4 ratio of about 0.1 to 50. It is.

Example 3゜SiH4:Ft:Ht:He-1:10:20
A silicon crystal thin film was formed in the same manner as in Example 1, except that the thickness was set to 100.

The electron mobility of the obtained thin film was 1,050 ca/volt・
It was determined to be single crystal silicon by Rf (RED).

Example 4 Raman half-value widths of films obtained by changing the substrate temperature under the film forming conditions of Example 1 were measured.

The dependence of the Raman half-value width on the substrate temperature was as shown in FIG.

Example 5゜As a result of measuring the Raman half-width of films obtained by changing the power density under the film-forming conditions of Example 1, good results were obtained at a power density of about 0.1 to 5 W/cm''. It has been found.

Example 6 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. 3 was fabricated.

The substrate is N type with a resistivity of 0.0015Ω/cm.
A non-doped epitaxial thin film with a thickness of 1.0 μm was formed under the same conditions as in Example 1 using a low-resistance silicon substrate.

As shown in FIG. 4, the rectification characteristics of the obtained diode are such that the rise of the forward direction ix current is steep, and the n value is about 1.
It was 1. Also, the rectification ratio at an applied voltage of 0.5V is 6.
There was also a strong order 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 7゜C using the Schottky diode obtained in Example 5
When the defect density Nd in the epitaxial thin film was measured by the -■ method, it was verified that the defect density Nd was about 2×101s/cffl, which was good.

Example 8 A silicon crystal thin film of 2.1 μm was formed under the same conditions as in Example 1 except that glass was used as the substrate. RHE
As a result of ED measurement, it was found that the obtained thin film was polycrystalline, but the electron mobility was 15c = d/volt-second, which was confirmed to be better than that of conventional polycrystalline thin films. .

[Brief explanation of the drawing]

Figure 1 shows Raman half-width and F! It is a graph which shows the relationship with the ratio of /S i H. FIG. 2 is a graph showing the dependence of Raman half-width on substrate temperature. FIG. 3 is a conceptual diagram of the Schottky diode produced in Example 5. In FIG. 3, reference numeral 1 represents a substrate, 2 represents an epitaxial thin film, 3 represents an indium electrode, and 4 represents a gold electrode. FIG. 4 shows the rectification characteristics of the epitaxial film produced in Example 5. In the figure, the * mark indicates the case where the voltage is applied in the forward direction, and the ○ mark 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 growing a silicon crystal thin film on a heated substrate by converting a reactive gas containing a raw material having silicon atoms into plasma using a plasma CVD method, the reactive gas contains at least silicon hydride and nitrogen as a film-forming gas. It is a mixed gas consisting of fluorine gas as an etching gas diluted with an active gas, and the reaction is carried out in the reaction chamber so that the amount of the etching gas is about 0.1 to 50 times the amount of the film forming gas. A method for producing a silicon crystal thin film, which comprises supplying a gas to generate plasma and forming a silicon crystal thin film on a substrate maintained at a constant temperature between about 100 and 700°C.