Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-07-09
2001-11-13
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S059000, C257S072000, C257S408000, C257S410000, C257S411000, C257S353000
Reexamination Certificate
active
06316810
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device typified by a thin film transistor and to a fabrication method thereof. Specifically, the present invention relates to a semiconductor device using a crystal silicon thin film formed on a glass substrate or a quartz substrate and to a fabrication method thereof.
2. Description of Related Art
Hitherto, there has been known a thin film transistor using a silicon film, i.e. a technology for forming the thin film transistor by using the silicon film formed on a glass substrate or quartz substrate.
The glass substrate or quartz substrate is used because the thin film transistor is used for an active matrix type liquid crystal display. While a thin film transistor has been formed by using an amorphous silicon film in the past; it is being tried to fabricate the thin film transistor by utilizing a silicon film having a crystalinity (referred to as “crystal silicon film” hereinbelow) in order to enhance its performance.
The thin film transistor using the crystal silicon film allows to operate at high speed by more than two digits as compared to one using the amorphous silicon film. Therefore, while peripheral driving circuits of an active matrix liquid crystal display have been composed of external IC circuits, they may be built on the glass substrate or quartz substrate similarly to the active matrix circuit.
Such structure is very advantageous in miniaturizing the whole apparatus and in simplifying the fabrication process, thus leading to the reduction of the fabrication cost.
In general, a crystal silicon film has been obtained by forming an amorphous silicon film by means of plasma CVD or reduced pressure thermal CVD and then by crystallizing it by implementing a heat treatment or by irradiating laser light.
However, it has been the fact that it is difficult to obtain a required crystalinity across the wide area through the heat treatment because it may cause nonuniformity in the crystallization.
Further, although it is possible to obtain the high crystalinity partly by irradiating laser light, it is difficult to obtain a good annealing effect across the wide area. In particular, the irradiation of the laser light is apt to become unstable under the condition for obtaining the good crystalinity.
Meanwhile, a technology described in Japanese Patent Laid-Open No. Hei. 6-232059 has been known. This is a technology which allows to obtain a crystal silicon film through a heat treatment at a lower temperature than that of the prior art by introducing a metal element (e.g. nickel) which promotes the crystallization of silicon to the amorphous silicon film.
According to studies conducted by the inventors et. al. it has been found that the crystal silicon film obtained by this method has crystalinity which is good for practical use across the wide area.
However, it has been also found that because the metal element is contained within the film and the amount thereof to be introduced has to be controlled very carefully, there is a problem in its reproducibility and stability (electrical stability of a device obtained).
Further, there is a problem that an elapsed change of the characteristics of a semiconductor device to be obtained is large or an OFF value, in case of a thin film transistor, is large, for example due to the influence of the remaining metal element.
That is, although the metal element which promotes the crystallization of silicon plays the useful role in obtaining the crystal silicon film, its existence becomes a minus factor which causes various problems after obtaining the crystal silicon film once.
PROBLEMS TO BE SOLVED BY THE INVENTION
It is an object of the invention disclosed in the present specification to provide a technology for reducing concentration of metal element within a crystal silicon film obtained by utilizing the metal element which promotes crystallization of silicon.
It is another object of the present invention to provide a technology which can enhance characteristics and reliability of a semiconductor device thus obtained.
MEANS FOR SOLVING THE PROBLEMS
One of the invention disclosed in the present specification is characterized in that it comprises steps of intentionally introducing metal element which promotes crystallization of silicon to an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment to obtain a crystal silicon film; eliminating or reducing the metal element existing within the crystal silicon film by implementing a second heat treatment within an oxidizing atmosphere containing a halogen element; eliminating a thermal oxide film formed in the previous step; and forming another thermal oxide film on the surface of the domain from which the thermal oxide film has been eliminated by implementing another thermal oxidation.
An arrangement of another invention is characterized in that it comprises steps of intentionally introducing metal element which promotes crystallization of silicon to an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment to obtain a crystal silicon film; eliminating or reducing the metal element existing within the crystal silicon film by implementing a second heat treatment within an oxidizing atmosphere containing a halogen element to form a thermal oxide film on the surface of the crystal silicon film and by causing the thermal oxide film to getter the metal element; eliminating the thermal oxide film formed in the previous step; and forming another thermal oxide film on the surface of the domain from which the thermal oxide film has been eliminated by implementing another thermal oxidation.
An arrangement of another invention is characterized in that it comprises steps of intentionally introducing a metal element which promotes crystallization of silicon to an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment to obtain a crystal silicon film; eliminating or reducing the metal element existing within the crystal silicon film by implementing a second heat treatment within an oxidizing atmosphere containing a halogen element; eliminating a thermal oxide film formed in the previous step; forming an active layer of a thin film transistor by implementing patterning; and forming another thermal oxide film which composes at least a part of a gate insulating film on the surface of the active layer by means of thermal oxidation.
An arrangement of another invention is characterized in that it comprises steps of selectively introducing a metal element which promotes crystallization of silicon to an amorphous silicon film; growing crystal by a first heat treatment in a direction parallel to the film from the domain to which the metal element has been selectively introduced; forming a thermal oxide film on the surface of the domain where the crystal has been grown by implementing a second heat treatment within an oxidizing atmosphere containing a halogen element; eliminating the thermal oxide film; and forming an active layer of the semiconductor device by using the domain from which the thermal oxide film has been eliminated.
In the invention disclosed in the present specification, one or a plurality elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au may be used as the metal element which promotes the crystallization of silicon.
Further, as the oxidizing atmosphere containing the halogen element, an atmosphere to which one or a plurality of gases selected from HCl, HF, HBr, Cl
2
, F
2
or Br
2
is added into the O
2
atmosphere or an atmosphere containing O
2
may be used.
An arrangement of another invention is characterized in that a semiconductor device has a crystal silicon film interposed between a first and second oxide films; the crystal silicon film contains hydrogen and a halogen element as well as a metal element which promotes crystallization of silicon; and the metal element is distributed in high concentration near the interfaces with the first/second oxide
Hayakawa Masahiko
Koyama Jun
Ogata Yasushi
Osame Mitsuaki
Teramoto Satoshi
Abraham Fetsum
Costelli Jeffrey L.
Nixon & Peabody LLP
Semiconductor Energy Laboratory Co,. Ltd.
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