Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Non-single crystal – or recrystallized – material with...
Reexamination Certificate
1997-02-24
2002-04-23
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Non-single crystal, or recrystallized, material with...
Reexamination Certificate
active
06376862
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device as typified by a thin-film transistor formed on a substrate, as well as to a manufacturing method thereof.
2. Description of Related Art
The thin-film transistor using a silicon film is known. In this technique, a thin-film transistor is formed by using a silicon film formed on a glass or quartz substrate.
The reason for using a glass or quartz substrate is that thin-film transistors are used for an active matrix liquid crystal display device. Conventionally, thin-film transistors are formed by using an amorphous silicon film. However, to provide higher performance, it is now attempted to form thin-film transistors by using a silicon film having crystallinity (called a crystalline silicon film).
A thin-film transistor using a crystalline silicon film can operate faster than that using an amorphous silicon film by two or more orders. Therefore, by employing thin-film transistors using a crystalline silicon film, peripheral drivers circuits of an active matrix liquid crystal display device, which are conventionally external IC circuits, can be formed on a glass or quartz substrate with an active matrix circuit.
The above configuration is very advantageous in terms of miniaturization of the entire device and simplification of a manufacturing process as well as reduction in manufacturing cost.
A crystalline silicon film is obtained by forming an amorphous silicon film through plasma CVD or low-pressure thermal CVD, and then crystallizing it through a heat treatment or irradiation with laser light.
However, with the heat treatment, it is currently difficult to obtain a desired level of crystallinity over a wide area; for example, crystallization is uneven.
On the other hand, although the method using the laser light irradiation can provide superior crystallinity partially, it is difficult for even such a technique to provide good annealing effects over a wide area. In particular, irradiation with laser light under such conditions as to provide a high degree of crystallinity tends to be unstable.
A technique described in Japanese Unexamined Patent Publication No. Hei. 6-232059 is known as a method for solving the above problems. In this technique, a metal element (for instance, nickel) for accelerating crystallization of silicon is introducing an amorphous silicon film, thereby providing a crystalline silicon film by a heat treatment of a lower temperature than in conventional techniques.
Studies of the present inventors have proved that a crystalline silicon film produced by this technique has, over a wide area, sufficiently high crystallinity to be suitable for practical use.
However, this technique has a problem that delicate control is needed for the introduction amount of a metal element because it remains in a resulting film. Accordingly, it has been found that this technique is problematic in reproducibility and(electrical stability of a device produced.
In addition, there is a problem that the characteristics of a semiconductor device produced considerably varies with time, which is an influence of a residual metal element. The residual metal element also causes a problem that the off-current of a thin-film transistor fabricated by using the above-mentioned film is large.
That is, although the metal element for accelerating crystallization of silicon is very useful to form a crystalline silicon film, it is associated with negative factors that cause various problems after formation of a crystalline silicon film.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a technique for reducing the concentration of a metal element for accelerating crystallization of silicon in a crystalline silicon film formed by utilizing the metal element. Another object of the invention is to provide a thin film semiconductor device having superior electrical characteristics by utilizing the film formed in the present invention.
According to one aspect of the invention, there is provided a manufacturing method of a semiconductor device, comprising the step of forming a crystalline silicon film on a substrate by using a metal element for accelerating crystallization of silicon, wherein during the step, a maximum process temperature (the highest temperature during the process) is higher than 650° C. and lower than 1,000° C., and a process time not shorter than one hour; the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; and the substrate has a strain point of 650°-1,000° C.
According to another aspect of the invention,there is provided a manufacturing method of a semiconductor device, comprising the step of forming a crystalline silicon film on a substrate by using a metal element for accelerating crystallization of silicon, wherein during the step, a maximum process temperature be higher than 700° C. and lower than 980° C. and a process time be not shorter than 30 minutes.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device, comprising the steps of forming a crystalline silicon film on a substrate by using a metal element for accelerating crystallization of silicon; and removing the metal element from the crystalline silicon film by forming a thermal oxidation film containing a halogen element, wherein each of the two steps has a maximum process temperature that is higher than 650° C. and lower than 1,000° C., and a process time not shorter than one hour; the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; and the substrate has a strain point of 650°-1,000° C.
According to a further aspect of the invention, there is provided a semiconductor device using a substrate, wherein the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; and the substrate has a strain point of 650°-1,000° C.
According to another aspect of the invention, there is provided a semiconductor device comprising a silicon thin film formed on a substrate, wherein the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; the substrate has a strain point of 650°-1,000° C.; the silicon thin film contains a metal element that accelerates crystallization of silicon at a concentration of 1×10
16
to 5×10
19
cm
−3
, the metal element existing at a high concentration in the vicinity of a interface of the silicon thin film.
Where a metal element for accelerating crystallization of silicon is used, the concentration of the residual metal element in a resulting crystalline silicon film is within the above range. If a crystalline silicon film contains a metal element at a higher concentration than the above range, it is too much influenced by the metal element to exhibit semiconductor characteristics. Further, the reliability of a semiconductor device is extremely lowered.
According to still another aspect of the invention, there is provided a semiconductor device comprising a silicon thin film formed on a substrate, wherein the substrate contains OH group at 50-2,000 ppm and chlorine at 10-1,000 ppm; the substrate has a strain point of 650°-1,000° C.; the silicon thin film contains a metal element that accelerates crystallization of silicon at 1×10
16
to 5×10
19
cm
−3
, and a halogen element at not less than 1×10
16
cm
−3
.
Where a thermal oxidation film is formed by a heat treatment in an atmosphere containing a halogen element, the halogen element enters into a crystalline silicon film during the formation of the thermal oxidation film. As a result, the halogen element is contained in the crystalline silicon film at not less than 1×10
16
cm
−3
. It is preferred that the upper limit of the concentration of the halogen element be about 5×10
20
cm
−3
.
According to a further aspect of the invention, there is provided a semiconductor device comprising a silicon thin film formed on a substrate, wherein the substrate has a strain point of 650°-1,000° C.; and the silicon thin film conta
Chaudhuri Olik
Fish & Richardson P.C.
Semiconductor Energy Laboratory Co,. Ltd.
Wille Douglas A.
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