Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
2000-12-08
2002-12-31
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S084000, C117S102000, C117S105000
Reexamination Certificate
active
06500256
ABSTRACT:
RELATED APPLICATION
The present application claims priority to Japanese Application No. P11-352349 filed Dec. 10, 1999, which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a single-crystal silicon layer, its epitaxial growth method and semiconductor, which are suitable for use in thin-film transistors (TFT), for example.
2. Description of the Related Art
Heretofore, a typical method for epitaxially growing a single crystal silicon (Si) layer is to decompose and grow silane (SiH
4
), dichlorosilane (Si
2
Cl
2
H
4
), trichlorosilane (SiCl
3
H
4
), silicon tetrachloride (SiCl
4
), or the like, under the temperature of about 700 through 1200° C., hydrogen atmosphere, pressure of 1.33×10
4
to 1×10
5
Pa (100 to 760 Torr) by using chemical vapor deposition (CVD).
However, the method of epitaxially growing a single crystal silicon layer by conventional CVD mentioned above involves the problem that the growth temperature is high. More specifically, in CVD, since energy required for chemical interaction and growth during epitaxial growth of a single crystal silicon layer is all supplied in form of heat energy obtained by heating a substrate to a high temperature, decreasing the growth temperature to or below 700° C. will invite a crystallographic deterioration and a decrease of the growth rate. Therefore, it is not possible to decrease the growth temperature from about 700° C. Further, when the growth temperature is in the range of about 1000 to 1200° C., the ratio of decomposed reactant gas (silane, dichlorosilane, or the like) contributing to epitaxial growth of a single crystal silicon layer is around 1 to 5%. When the growth temperature is 800° C., it further decreases to around 0.1 to 0.5%. Thus the efficiency of use of reactive gas is seriously low, and it invites an increase of its cost. Furthermore, since exhaust reactant gas (silane, dichlorosilane, and so forth) are harmful, a process for change it harmless, such as burning or absorption, is required to prevent the reactant gas from being released in the air. Therefore, when the efficiency of the use of the reactant gas seriously decreases as indicated above, the expense for the process for changing it harmless also increases.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a epitaxial growth method of a single crystal silicon layer capable of epitaxially growing a high-quality single crystal silicon layer at a temperature lower than that of conventional CVD; a single crystal silicon layer obtained by the method; and a semiconductor device using such a single crystal silicon layer.
The Inventor made researches toward solution of the above problems involved in conventional techniques. These researches are outlined below.
Recently, as a growth method of polycrystalline silicon layers and amorphous silicon layers, a growth method called catalytic CVD are being remarked (for example, Japanese Patent Laid-Open Publication No. hei 10-83988 and Applied Physics, Vol. 66, No. 10, p. 1094(1997)). This catalytic CVD uses catalytic cracking reaction between a heated catalyst and reactant gas (source material gas).
The Inventor made consideration about application of catalytic CVD to epitaxial growth of a single crystal silicon layer. That is, catalytic CVD, in its first stage, brings reactant gas (such as silane and hydrogen in case of using silane as the source material of silicon) into contact with a hot catalyst heated to 1600 through 1800° C., for example, to activate the reactant gas and thereby make silicon atoms, or clusters of silicon atoms, and hydrogen atoms, or clusters of hydrogen atoms, having high energies, and in its second stage, raises the temperature of these silicon atoms and hydrogen atoms or molecules having high energies, or a substrate that supplies their clusters, to a high temperature, thereby to supply and support the energy required particularly for silicon atoms to align along the crystalline orientation of the substrate. Therefore, catalytic CVD enables epitaxial growth of a single crystal silicon layer even at a lower temperature than that of conventional CVD, such as around 350° C., for example.
However, according to results of various experiments made by the Inventor, in the case where a single crystal silicon layer is epitaxially grown at a low temperature by existing catalytic CVD, oxygen is more liable to be brought into the growth layer than that epitaxially grown by conventional CVD, and the oxygen concentration in the single crystal silicon layer obtained often exceeds several atomic % (at %). This amounts at least to 5×10
20
atoms/cm
3
(atoms/cc) when converted into atomic concentration. Since the maximum solution of oxygen in silicon is 2.5×10
18
atoms/cc (for example, Semiconductor Handbook 2nd Edition, pp.128-129, edited by Hisayoshi Yanai, Ohmusha, 1977), and the said oxygen concentration is far beyond the maximum solution of oxygen in silicon, 2.5×10
18
atoms/cc. When oxygen over the maximum solution is contained in silicon, oxygen precipitates forming silicon oxide, and sometimes results in forming an oxide thin film around silicon crystal grains or sometimes results in forming oxide grains with a further increase of oxygen.
Under the circumstances, the Inventor made researches about growth conditions for epitaxial growth of a single crystal silicon layer by catalytic CVD toward obtaining a high-quality single crystal silicon layer.
That is, repeated were experiments of epitaxially growing single crystal silicon layers by using catalytic CVD and variously changing process conditions under a low temperature range (200 through 600° C.) and then evaluating them. As a result, it was found that, for growing high-quality single crystal silicon layers by catalytic CVD, conditions such as pressure of the vapor-phase growth atmosphere, partial pressure of oxygen and moisture in the growth atmosphere, and soon, were absolutely different from those of conventional CVD. More specifically, at least in the initial period of growth, the total pressure of the growth atmosphere was set to a much lower pressure than that of existing catalytic CVD, e.g., in the range from 1.33×10
−3
Pa to 4 Pa (from 0.01 mTorr to 30 mTorr), it was confirmed that the maximum oxygen concentration at least near the boundary with the substrate was as very low as 3×10
18
atoms/cc (0.006 at %), and high-quality single crystal silicon layers could be grown. Also when the partial pressure of oxygen and moisture in the growth atmosphere at least in the initial period of growth was set in the range from 6.65×10
−10
Pa to 2×10
−6
(from 0.005×10
−6
mTorr to 15×10
−6
mTorr), it was confirmed that the oxygen concentration at least near the boundary with the substrate was similarly as very low as 3×10 atoms/cc (0.006 at %), and high-quality single crystal silicon layers could be grown. This partial pressure of oxygen and moisture can be obtained when oxygen and moisture around 0.5 ppm in total are contained in the reactant gas.
The present invention has been made through studies based on the above knowledge of the Inventor.
According to the first aspect of the invention, there is provided a single crystal silicon layer epitaxially grown by catalytic CVD on a material layer in lattice alignment with single crystal silicon, characterized in:
the maximum oxygen concentration thereof being 3×10
18
atoms/cm
3
at least in a region having the thickness of 10 nm thick from the boundary between the material layer and the single crystal silicon layer.
In the first aspect of the invention, the maximum oxygen concentration at least in a region with the thickness of 10 nm from the boundary between the material layer in lattice alignment with single crystal silicon and the single crystal silicon layer is preferably not higher than 2×10
18
atoms/cm
3
. Further, the maximum oxyg
Yamanaka Hideo
Yamoto Hisayoshi
Hiteshew Felisa
Sonnenschein Nath & Rosenthal
Sony Corporation
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