Method for fabricating silicon thin film

Details Method for fabricating silicon thin film Method for fabricating silicon thin film

1999-03-15

2001-10-30

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Forming from vapor or gaseous state

With decomposition of a precursor

C117S088000, C117S093000, C117S102000

Reexamination Certificate

active

06309458

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a method for growing a silicon thin film on a semiconductor single crystal substrate.
As the method for growing a silicon thin film on a semiconductor single crystal substrate, there has been used a method in which with a silicon raw material gas supplied, a silicon thin film is grown on a semiconductor single crystal substrate by a vapor phase growth process.
FIG. 1
shows an example of the apparatus for fabricating silicon thin films. For forming a silicon thin film with this apparatus, a semiconductor single crystal substrate
1
such as a silicon semiconductor single crystal substrate is placed in a process vessel (reaction vessel)
10
made of quartz glass or the like, and infrared light is irradiated to the semiconductor single crystal substrate
1
by energizing an infrared lamp
11
provided outside the process vessel
10
, so that the temperature of the semiconductor single crystal substrate
1
is increased to a desired temperature, for example, 950° C. or 1000° C. Then, a silicon raw material gas
3
given by a dilution gas such as hydrogen gas diluted with trichlorosilane (SiHCl
3
) or the like is introduced through a gas inlet
12
, by which a silicon thin film such as a silicon single crystal thin film or the like is grown on a surface of the semiconductor single crystal substrate
1
maintained at the high temperature. Also, for adjustment of the resistivity of the silicon thin film, diborane gas (B
2
H
6
) or phosphine gas (PH
3
) or the like is introduced together. As the silicon material, dichlorosilane (SiH
2
Cl
2
) or silicon tetrachloride (SiCl
4
) may be used, in some cases, instead of trichlorosilane (SiHCl
3
).
In addition, for prevention of silicon deposition on the wall of the process vessel
10
due to the reaction of the silicon material, the temperature of the wall of the process vessel
10
is controlled by absorbing heat from the process vessel
10
by making a flow of a coolant
4
such as low-temperature air or nitrogen gas. The temperature of the semiconductor single crystal substrate
1
is measured, for example, by a radiation thermometer
2
provided outside the process vessel
10
.
It has conventionally been known that, in the method for growing a silicon thin film by supplying a silicon raw material gas formed by diluting hydrogen gas with trichlorosilane (SiHCl
3
) as described above, trichlorosilane (SiHCl
3
) decomposes into SiCl
2
in vapor phase, which is an important reaction intermediate that accelerates the principal chemical reaction in the growth of the silicon thin film. Further, it has also been reported that silicon tetrachloride (SiCl
4
) is generated in association with this reaction (for example, J. Nishizawa and M. Saito, J. Crystal growth, Vol. 52, pp. 213-218, 1981).
Silicon tetrachloride (SiCl
4
), which, once formed, is relatively stabler to heat than trichlorosilane (SiHCl
3
), decreases in the rate of contribution to the formation of the silicon thin film, which has been a cause of reducing the supply efficiency of the silicon material. Also, silicon tetrachloride (SiCl
4
) yields large numbers of hydrogen chloride molecules each time one silicon atom from one molecule thereof is contributed to the growth of the silicon thin film, which has been a cause of undesirable results such as the formation of small voids at the surface of the silicon thin film.
Therefore, an object of the invention is to provide a method for fabricating a silicon thin film with a high supply efficiency of silicon material.
SUMMARY OF THE INVENTION
In order to achieve the above object, the inventors have made investigations and researches based on results of basic experiments, having reached the following invention.
In order to achieve the above object, the invention provides a method for fabricating a silicon thin film on a semiconductor single crystal substrate by placing the semiconductor single crystal substrate in a process vessel and by supplying a silicon material into the process vessel, characterized by comprising a step of cooling a wall of the process vessel so that silicon tetrachloride (SiCl
4
) concentration in an exhaust gas discharged from the process vessel during a growth process of a silicon thin film becomes equal to or lower than {fraction (1/10)} of a concentration of the silicon material in the exhaust gas.
Preferably, the wall of the process vessel is cooled so that temperature gradient of a vapor phase between a surface of the semiconductor single crystal substrate and the wall of the process vessel satisfies the following Equation (1) in relation to a temperature of said semiconductor single crystal substrate:
temperature gradient(K/cm)≧0.3×substrate temperature(K)−90  (1).
Preferably, the temperature of the semiconductor single crystal substrate is equal to or higher than 800° C.
Preferably, the silicon material is trichlorosilane (SiHCl
3
).
Preferably, the semiconductor single crystal substrate is a silicon semiconductor single crystal substrate and the silicon thin film is a silicon single crystal thin film.
In the method of the invention, the concentration of silicon tetrachloride (SiCl
4
) is made equal to or lower than {fraction (1/10)} of the concentration of the supplied silicon material in the exhaust gas exhausted from the process vessel during the growth process of a silicon thin film in the process vessel, so that the supply efficiency of the silicon material is increased. Therefore, the growth rate of the silicon thin film can be improved even though the supply amount of the silicon material is the same as the conventional one.
In an embodiment of the invention, by increasing the heightwise temperature gradient on above the semiconductor single crystal substrate, chemical reaction in the vapor phase in regions separate away from the surface of the semiconductor single crystal substrate can be suppressed so that any losses of trichlorosilane (SiHCl
3
) or the like due to the generation of silicon tetrachloride (SiCl
4
) can be suppressed. Also, since the region where SiCl
2
is generated in the vapor phase can be limited to a region in close proximity to the surface of the semiconductor single crystal substrate, dissipation of SiCl
2
into the vapor phase separate away from the surface of the semiconductor single crystal substrate can be suppressed. Accordingly, the supply efficiency of the silicon material can be improved.
In an embodiment of the invention, by making the temperature of the semiconductor single crystal substrate equal to or higher than 800° C. and by making the temperature gradient satisfying the above Equation (1), generation of silicon tetrachloride (SiCl
4
) and dissipation of SiCl
2
can be prevented without lowering the reaction efficiency of chemical reaction just above the surface of the semiconductor single crystal substrate.


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Wolf et al., Silicon Processing for the VLSI Era, vol. 1: Process Technology, Lattice Press, Sunset Beach, CA, pp. 142-143, 166-170, 1986.*
Nishizawa et al. Journal of Crystal Growth, Mechanism of Chemical Vapor Deposition of Silicon, vol. 52, pp. 213-218, 1981.*
Wolf et al., Silicon Processing for the VLSI Era vol. 1: Process Technology, Latice Press, Sunset Beach, CA, USA, pp. 124-143, 166-170, 1986.*
Nishizawa, J., Mechanism of Chemical Vapor Deposition of Silicon Journal of Crystal Growth 52, North-Holland Publishing Co. 1pp. 213-218, 1981.

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