Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
2001-08-29
2004-03-23
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S094000, C117S101000, C117S105000, C117S935000, C118S715000, C118S722000, C427S255110, C427S255120, C427S255270
Reexamination Certificate
active
06709512
ABSTRACT:
RELATED APPLICATION DATA
The present application(s) claim(s) priority to Japanese Application(s) No(s). P2000-261396 filed Aug. 30, 2000, which application(s) is/are incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of growing a polycrystalline silicon layer, a method of epitaxially growing a single crystal silicon layer, and a catalytic CVD apparatus, which are suitable for manufacturing, for example, a thin-film transistor (TFT).
2. Description of the Related Art
For fabricating a polycrystalline silicon (Si) layer, typically used heretofore was a method using atmospheric pressure chemical vapor deposition (APCVD) to decompose silane (SiH
4
) or disilane (Si
2
H
6
) under a temperature around 600 to 700° C., in hydrogen atmosphere and under the pressure of 1×10
5
Pa (760 Torr) and thereby grow the layer, a method using low-pressure chemical vapor deposition (LPCVD) to decompose and grow silane (SiH
4
) or disilane (Si
2
H
6
) under a temperature around 600 to 700° C., in hydrogen atmosphere and under the pressure of (0.53~1.33)×10
2
Pa (0.4~1 Torr) and thereby grow the layer, or a method using plasma CVD to decompose silane (SiH
4
) or disilane (Si
2
H
6
) under a temperature around 200 to 400° C., in a hydrogen atmosphere and under the pressure of (0.26~2.6)×10
2
Pa (0.2~2 Torr), thereby grow an amorphous silicon layer and thereafter anneal the amorphous silicon layer under a high temperature around 800 to 1300° C. so as to grow crystal grains.
However, those methods for growing polycrystalline silicon layers by APCVD and LPCVD involve the problem that their growth temperatures are high. In APCVD and LPCVD, since all of the energy required for chemical interaction and growth during growth of polycrystalline silicon layers is supplied in form of heat energy by heating, the growth temperature cannot be largely decreased from about 600° C. Additionally, since interaction efficiency of reactant gas like silane is generally as low as several t or less, almost all of such reactant gas is discharged and discarded, cost of reactant gas becomes high and cost required for the discard is also high. On the other hand, the method for fabricating a polycrystalline silicon layer by crystallizing an amorphous silicon layer involves the problem that it additionally needs an annealing apparatus for high-temperature annealing.
Recently, as a growth method of polycrystalline silicon layers overcoming those problems, a growth method called catalytic CVD are being remarked (for example, Japanese Laid-Open Publication No. sho 63-40314, Japanese Patent Laid-Open Publication No. hei 8-250438, 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). 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 form single-crystal grains. Therefore, catalytic CVD enables growth of a polycrystalline silicon layer even at a lower temperature than those of conventional APCVD and LPCVD, such as around 350° C., for example.
However, according to results of various experiments made by the Inventor, in the case where a polycrystalline silicon layer is grown at a low temperature by existing catalytic CVD, metal impurities more easily enter into the growth layer than in growth layers grown by conventional APCVD and LPCVD, and containment of high-concentrated metal impurities in the resultant polycrystalline silicon layer is a problem this technique involves. These contained metal impurities amount to, for example, 2×10
17
~2×10
18
atoms/cc, of tungsten (W), 7×10
15
~2×10
17
atoms/cc of iron (Fe), 9×10
14
~3×10
16
atoms/cc of chromium (Cr), and less than 3×10
18
atoms/cc of nickel(Ni). In contrast, concentrations of metal impurities contained in a polycrystalline silicon layer grown by conventional APCVD or LPCVD are less than 1×10
15
atoms/cc of W, typically around 5×10
16
atoms/cc of Fe, typically less than 3×10
14
atoms/cc of Cr, and typically less than 6×10
19
atoms/cc of Ni. Thus it is recognized how high the concentration of metal impurities contained in the polycrystalline silicon layer grown at a low temperature by catalytic CVD. Polycrystalline silicon layers containing metal impurities to a high concentration exhibit bad electric properties, such as having a low electron mobility, and when they are used as polycrystalline silicon layers for TFT, for example, it is difficult to operate the TFT at a high speed.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a polycrystalline silicon layer growth method that can grow a polycrystalline silicon layer remarkably low in concentration of metal impurities contained therein.
Another object of the invention is to provide a single crystal layer epitaxial growth method that can epitaxially grow a single crystal silicon layer remarkably low in concentration of metal impurities contained therein.
Still another object of the invention is to provide a catalytic CVD apparatus that can grow a polycrystalline silicon layer and a single crystal silicon layer remarkably low in concentration of metal impurities contained therein.
The Inventor made researches toward solution of the above problems involved in conventional techniques. These researches are outlined below.
According to the Inventor's researches, it is considered that W, Fe, Cr and Ni contained in polycrystalline silicon layers grown by conventional catalytic CVD derived exclusively from catalysts. Among them, W is the component element of a catalyst itself whereas Fe, Cr and Ni are considered to have been contained as impurities in the W material. W has a very high melting point as high as 3380° C. and a low vapor pressure, its amount taken into the growth layer is not considered to be so much. Actually, however, since oxidizing substances like O
2
and H
2
O exist in the growth chamber of the catalytic CVD apparatus, W forming the catalyst will be oxidized to tungsten oxide when the catalyst is heated to a high, and tungsten oxide having a high vapor pressure will vaporize and will be taken into the growth layer.
Through various experiments, the Inventor reached the conclusion that, in order to prevent or minimize ingestion of metal impurities into a growth layer, it would be most effective to form a barrier layer on the surface of the catalyst to prevent separation of disengagement of component elements or impurities from the catalyst when it is heated to a high temperature for growth and that a carbide or a carbide would be preferable as the barrier layer from the viewpoint of heat resistance and easiness of its formation. It is sufficient for the barrier layer to exist on the surface of the catalyst at least upon the start of growth. It may be previously formed before placing the catalyst in the catalytic CVD apparatus, or may be formed before the growth is started after the catalyst is placed in the catalytic CVD apparatus.
The present invention has been made as a result of researches based on the Inventor's own knowledge.
According to the first aspect of the invention, there is provided a polycrystalline silicon layer growth method for growing a polycrystalline silicon layer on a substrate by catalyt
Yamanaka Hideo
Yamoto Hisayoshi
Depke Robert J.
Holland & Knight LLP
Kunemund Robert
Sony Corporation
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