Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2000-07-12
2003-11-04
Nhu, David (Department: 2818)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S905000, C438S680000
Reexamination Certificate
active
06642091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of fabricating a thin-film semiconductor device and an apparatus for fabricating the same, and more particularly to a method of forming a thin silicon film used for a crystalline silicon thin-film transistor, and an interface between semiconductor and an insulating film, used for a field effect transistor, and further to an apparatus of fabricating such a thin silicon film and such an interface.
2. Description of the Related Art
Japanese Patent Publication No. 7-118443 has suggested a method including the step of radiating laser beam having a short wavelength, to an amorphous silicon thin film formed on an amorphous substrate, to thereby fabricate a thin film transistor. The method makes it possible to crystallize amorphous silicon without wholly heating the substrate, and hence, makes it possible to fabricate a semiconductor device or a semiconductor integrated circuit on a substrate having a wide area such as a substrate to be used for a liquid crystal display, or a cheap substrate such as glass.
Japanese Unexamined Patent Publication No. 9-320961 has suggested a method of fabricating a thin-film transistor. In this method, the steps of forming an amorphous silicon thin film to which laser beam is to be radiated, radiating laser beam to the amorphous silicon thin film, carrying out hydrogenation in plasma, and forming a gate insulating film are carried out in this sequence or other sequences without exposure to atmosphere.
The Publication also discloses an apparatus of fabricating a semiconductor thin film, including a first chamber in which a substrate is loaded in vacuum, a second chamber in which silicon is formed, a third chamber in which laser beam is radiated, a fourth chamber in which an insulating film is formed, a fifth chamber in which annealing is carried out in hydrogen atmosphere, a sixth chamber in which a substrate is unloaded, and a seventh chamber through which a substrate is transferred to other chambers.
A glass substrate is transferred into the apparatus from the first chamber. The glass substrate can be transferred to any one of the chambers through the seventh chamber and a vacuum valve. The first to seventh chambers are equipped with a gas exhaust system independently of one another, and hence, can exhaust reactive gas, inert gas and other gases introduced from gas introducers in the steps of forming a silicon film, forming an insulating film, and annealing.
When a substrate is transferred out of any one of the chambers, the chamber is sufficiently exhausted. When the chamber has almost the same pressure as that of the seventh chamber, a vacuum valve is released, and then, a substrate is taken out of the chamber by means of a robot. Then, the vacuum valve is closed.
The substrate is introduced into a next chamber having almost the same vacuum degree as that of the seventh chamber after releasing a vacuum valve, transferring the substrate into the third chamber, and closing the vacuum valve. After closing the vacuum valve, a process gas is introduced into the chamber, and a pressure and a temperature in the chamber are adjusted to a predetermined pressure and temperature. Then, laser beam is radiated to the substrate.
The substrate is transferred among the first to sixth chambers in such a manner as mentioned above. A plurality of substrates can be transferred among the chambers through the use of a plurality of robots, in which case, the chambers are sufficiently exhausted. A vacuum valve may be released and closed, and the substrate may be transferred after the chambers are caused to have almost the same pressure in inert gas, nitrogen gas or hydrogen gas atmosphere.
The substrate is transferred between the first chamber and atmosphere and further between the sixth chamber and atmosphere, after nitrogen or inert gas is leaked with the vacuum valve being closed, and a valve is released to thereby allow the first and sixth chambers to be in fluid communication with atmosphere.
Thus, all the steps are carried out without exposure to atmosphere. The reason is as follows. Since a surface of silicon formed by laser crystallization is quite active, contaminants are likely to be adhered to the surface, if the silicon is exposed to atmosphere. This results in degradation in performances of resultant TFT. As an alternative, there is dispersion among performances of TFT. In order to avoid such degradation or dispersion, all the steps are carried out without exposure to atmosphere.
The inventor conducted the experiment in which excimer laser crystallization and formation of a silicon dioxide film were carried out in the same apparatus in two cases in one of which a substrate was exposed to atmosphere and in the other of which a substrate was not exposed to atmosphere. Herein, “the same apparatus” includes a case in which a substrate is transferred to another apparatus without exposure to atmosphere. In the case in which a substrate was not exposed to atmosphere, a fabrication yield was much enhanced because dusts and particles were prevented from adhering to a product. However, it was also found out that such enhancement in a fabrication yield can be obtained by enhancing cleanness in a clean room. A fabrication yield was enhanced best in an film-forming apparatus including a washing device therein.
Comparing a trap level density in a silicon film to an interface level density (or density of electric charge in a fixed oxide film), the trap level density is obviously greater than the interface level density. That is, there is a problem of insufficiency in performances of a silicon film (or a trap level density) in order to have sufficient cleanness in a product having a silicon film and a gate insulating film both formed without exposure to atmosphere in the same apparatus.
The inventor analyzed the above-mentioned problem, and resultingly, found out the following problems in connection with steps of fabricating a silicon film and a gate insulating film and an apparatus of fabricating the same.
The first problem is as follows. For instance, in a cluster tool type apparatus suggested in Japanese Unexamined Patent Publication No. 7-99321, a plurality of chambers is arranged having its own purpose. Hence, it is quite difficult to keep a chamber located at a core, away from contaminants. There occurs cross-contamination in transfer of a substrate between chambers, even though the cross-contamination is slight.
The second problem is as follows. For instance, an in-line type apparatus suggested in Japanese Unexamined Patent Publication No. 5-182923 is accompanied with a problem that it is unavoidable generation of minute dust, in particular, metal particles due to a great frictional area between parts in vacuum.
The third problem is as follows. Silicon crystallized by laser beam would have a quite active surface. For instance, if silicon is coated with active species having energy, for instance, radical species such as hydrogen radical, oxygen radical, hydrogen ion, oxygen ion, ion species or ozone, after the silicon has been crystallized by laser beam, but before a gate insulating film is formed, contaminants adhered to a wall of a chamber and metal constituting a wall of a chamber are excited, resulting in that atmosphere in which a substrate is put is contaminated.
The fourth problem is that since laser radiation in oxidation atmosphere reflects dispersion in laser intensity in a step of introducing oxygen into silicon, there would be dispersion in a concentration of oxygen in a silicon film. This results in non-uniformity in characteristics of resultant silicon films.
The fifth problem is as follows. When a plurality of steps are to be successively carried out without exposure to atmosphere, for instance, steps of crystallizing a silicon film by means of laser beam and thereafter forming a gate insulating film, though it is possible to reduce contaminants adhered to the silicon film by not exposing the silicon film to atmosphere, the above-mentioned problems still interfere with
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