Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate
Reexamination Certificate
2000-11-30
2003-04-01
Zarabian, Amir (Department: 2822)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
C438S482000, C438S486000, C438S488000, C438S497000, C438S502000
Reexamination Certificate
active
06541354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of forming silicon films used for LSIs, thin-film transistors, and photosensitive members.
2. Description of Related Art
Conventionally, as methods for forming amorphous silicon films and polysilicon films, thermal CVD (Chemical Vapor Deposition), plasma-enhanced CVD, photo CVD, etc., using monosilane gas or disilane gas, are employed. In general, thermal CVD is widely used for polysilicon (refer to J. Vac. Sci. Technology., Vol. 14, p. 1082 (1977)), and plasma-enhanced CVD is widely used for amorphous silicon (refer to Solid State Com., Vol. 17, p. 1193 (1975)). The above methods are used in the fabrication of liquid crystal display devices provided with thin-film transistors, solar cells, etc.
SUMMARY OF THE INVENTION
However, in the formation of silicon films by CVD methods described above, further improvement in the process has been awaited for the reasons described below. 1) Since silicon particles are generated in a vapor phase due to the use of the vapor phase reaction, yield is decreased due to the contamination of apparatuses and the generation of extraneous matter; 2) since the raw material is gaseous, it is difficult to produce a film of uniform thickness on a substrate having an uneven surface; 3) since the film forms slowly, productivity is low; and 4) in plasma-enhanced CVD, complex and expensive high-frequency generators, vacuum systems, etc., are required.
Additionally, since a gaseous silicon hydride, which is highly toxic and reactive, is used, handling is difficult, and a closed vacuum system is required because of the gaseous nature of the material. In general, such apparatuses are large, and the apparatuses themselves are expensive, and also a large amount of energy is consumed by the vacuum system and the plasma system, resulting in higher production costs.
In contrast, recently, a method for coating a liquid silicon hydride in which a vacuum system is not used has been developed. Japanese Unexamined Patent Application Publication No. 1-29661 discloses a method for forming a silicon-based thin film, in which a gaseous raw material is liquefied and adsorbed on a cooled substrate, followed by reaction with atomic hydrogen which is chemically active. However, a complex apparatus is required in order to continuously vaporize and cool the raw material silicon hydride, and it is also difficult to control the thickness of the film.
Japanese Unexamined Patent Application Publication No. 7-267621 discloses a method for coating a liquid silicon hydride having a low molecular weight onto a substrate. However, in this method, handling is difficult due to the instability in the system, and because the material is liquid, it is difficult to obtain a film of uniform thickness when used for a substrate with a large surface area.
On the other hand, although United Kingdom Patent No. GB-2077710A discloses an example of a solid silicon hydride polymer, since the polymer is insoluble in solvents, it is not possible to form a film by coating.
Furthermore, Japanese Unexamined Patent Application Publication No. 9-237927 discloses a method in which a silicon film is separated by pyrolysis after a polysilane solution is applied onto a substrate for the purpose of fabricating solar cells. However, when a silicon compound containing carbon is subjected to pyrolysis or photolysis by ultraviolet light, since a large amount of carbon remains as impurities, it is difficult to obtain an amorphous or polycrystalline silicon film having superior electrical characteristics.
The silicon semiconductor film described above is usually used as a p-type or n-type semiconductor by doping Group III or Group V elements of the periodic table. Such doping is usually performed by thermal diffusion or ion implantation after a silicon film is formed. Since the doping is performed in a vacuum, process control is troublesome, and in particular, it is difficult to form a uniformly doped silicon film over a large substrate.
In contrast, Japanese Unexamined Patent Application Publication No. 9-237927 described above discloses a method for coating by adding an alkyl compound for imparting p-type or n-type conductivity to a polysilane solution or a method for pyrolyzing a film coated with a polysilane solution in an atmosphere containing a dopant source. However, in the former case, a film which is uniformly doped is not obtained due a difference in solubility between the polysilane and the alkyl compound containing the dopant, and a large amount of carbon remains as impurities in the final film because carbon is contained therein as described above. In the latter case, it is difficult to control the amount of doping.
It is an object of the present invention to provide a completely novel method for forming a desired silicon film in which vapor phase deposition, such as CVD, is performed onto a substrate which is heated and retained at a predetermined temperature, and after a solution containing a predetermined silicon compound is applied onto the substrate, the solvent is removed by heating or the like so as to form a coating film of the silicon compound, followed by decomposition in the film or further followed by laser irradiation to form a silicon film having characteristics of an electrical material on the substrate. In particular, it is also an object of the present invention to provide a method for forming a silicon film doped with boron or phosphorus over a large substrate in relation to the fabrication of a device in which, after a film composed of a modified silicon compound is formed by coating as a precursor of the silicon film, the silicon precursor film is transformed into semiconductor silicon by heat and/or light treatment in an inert atmosphere, and simultaneously, doping can be performed.
In accordance with the present invention, a first method for forming a silicon film includes the step of applying a solution containing a cyclic silicon compound represented by the formula Si
n
X
m
(where n is an integer of 5 or more, m is an integer of n, 2n−2, or 2n, and X is a hydrogen atom and/or halogen atom), onto a substrate.
In such a method, preferably, the method includes the steps of removing the solvent after the solution is applied, and performing pyrolysis and/or photolysis of the coating film, or further performing laser irradiation, and thus, the silicon film can be finally obtained.
In accordance with the present invention, a second method for forming a silicon film includes the step of applying a solution containing a modified silicon compound, which is represented by the formula Si
a
X
b
Y
c
(where X is a hydrogen atom and/or halogen atom, Y is a boron atom or phosphorus atom, a is an integer of 3 or more, b is an integer from a to 2a+c+2, and c is an integer from 1 to a), or a mixture of a silicon compound and the modified silicon compound, onto a substrate.
In such a method, preferably, the method includes the steps of removing the solvent after the solution is applied, and performing pyrolysis and/or photolysis of the coating film, or further performing laser irradiation, and thus, the silicon film modified by boron or phosphorus can be finally obtained.
By the methods described above, silicon films having superior characteristics as electronic materials can be obtained.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The present invention will be described in detail below.
The silicon compound used in the first method for forming the silicon film in the present invention is a cyclic silicon compound, which is represented by the formula Si
n
X
m
(where n is an integer of 5 or more, m is an integer of n, 2n−2, or 2n, and X is a hydrogen atom and/or halogen atom).
In particular, in the silicon compound represented by the formula Si
n
X
m
, preferably, n is 5 to 20, and more preferably, n is 5 or 6. If n is less than 5, since the silicon compound itself will be unstable due to strain resulting from the ring, handling is difficult. If n exceeds 20, solubility in the solution is de
Furusawa Masahiro
Matsuki Yasuo
Miyashita Satoru
Seki Shun-ichi
Shimoda Tatsuya
Guerrero Maria
Oliff & Berridge PLC.
Seiko Epson Corporation
Zarabian Amir
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