Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Field effect transistor
Reexamination Certificate
2001-02-26
2004-06-29
Fourson, George (Department: 2823)
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Field effect transistor
C438S150000
Reexamination Certificate
active
06756614
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film semiconductor device having a polycrystalline semiconductor film, and a process and apparatus for producing a polycrystalline semiconductor film. The thin film semiconductor device of the present invention is useful for image display devices.
2. Related Art
The prior art process for crystallizing an amorphous silicon thin film by scanning with a pulse laser will be described with reference to FIG.
12
.
FIG. 12
shows the most general process for crystallizing with an excimer pulse laser of the prior art. The whole substrate is crystallized by irradiating a non-crystal silicon film
102
which was formed on a substrate
100
through an base film
101
, with a laser beam
105
from a linear excimer laser having a width L of several millimeters on the substrate and moving the laser exposure position at intervals of 1 to several pulses. In this prior art process, crystal nuclei are formed at random upon laser exposure. In addition, the average distance between the formed crystal nuclei is 0.5 &mgr;m or less under ordinary laser annealing conditions. Therefore, the obtained polycrystalline silicon film
103
has a grain size of 0.5 &mgr;m or less and is not uniform in size.
Further, an international patent publication WO9745827 discloses the following process. That is, when the width L of the laser beam
105
shown in
FIG. 12
is reduced to 0.5 &mgr;m or less and the position of the laser beam
105
having this shape is moved 0.5 &mgr;m or less each time to irradiate pulses, crystal grows in one direction with the initially formed crystal grains as seeds. The above one direction is a transverse direction, that is, a direction perpendicular to the thickness direction of the grown film.
In the above process of the prior art, as the time required for crystal growth is 100 ns or less, the obtained crystals have a grain size of 1 &mgr;m or less and are greatly nonuniform in grain size. The orientation of grains is out of order, the density of defects is large, and the roughness of the film surface is large. Therefore, it is impossible to grow polycrystalline silicon having a large grain size or to control the grain size or the position of the grain boundary accurately. Therefore, the grain boundary is included in the channel at random. Consequently, it is difficult to improve the characteristic properties, reliability and uniformity of TFT devices.
Since the beam must be converged to a size of 1 &mgr;m or less in the technology disclosed by the above international patent publication WO9745827, the energy of the laser is lost and the optical system of an irradiation laser become complicated. As the moving distance between laser pulses is 1 &mgr;m or less, it takes a long time to crystallize the whole substrate and it is difficult to improve throughput and reduce costs. Particularly, this process cannot be applied to a large-area substrate. Further, very small distance movement is easily influenced by vibration and involves a yield problem.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a production process and apparatus for forming on an insulating substrate made from glass or the like a high-quality polycrystalline semiconductor film whose grain boundary, grain size and crystal orientation can be controlled and whose film roughness and crystal defects formed in crystallization process have been reduced, and to provide a thin semiconductor device comprising the above polycrystalline semiconductor film.
It is a second object of the present invention to provide a production process and apparatus for forming a low-cost and high-quality polycrystalline semiconductor film, which can reduce the number of production steps, can be applied to a large-area substrate and have a high throughput, and to provide a thin film semiconductor device comprising the above polycrystalline semiconductor film.
It is a third object of the present invention to provide a production process and apparatus for forming on an inexpensive insulating substrate made from glass or the like a high-quality polycrystalline semiconductor film which operates with high performance and high reliability and is excellent in uniformity among devices, and to provide a thin film semiconductor device comprising the above polycrystalline semiconductor film.
The major aspects of the present invention will be described below.
According to a first aspect of the present invention, there is provided a thin film semiconductor device which has an insulating substrate, a first semiconductor film which is a polycrystalline semiconductor film, a gate electrode formed on the first semiconductor film through a gate insulating film, first charge transmitting and receiving means and second charge transmitting and receiving means formed on the first semiconductor film at a predetermined interval therebetween, and a channel region formed between the first and second charge transmitting and receiving means, wherein
the main orientation of the first semiconductor film constituting the channel region is {110} with respect to the main surface of the insulating substrate or the gate insulating film.
It is possible to provide a thin film semiconductor device having high reliability by selecting the main orientation of the semiconductor film of the channel region with respect to the main surface of the insulating substrate or the gate insulating film even when a polycrystalline semiconductor film is used. The method of controlling the main orientation of the polycrystalline film will be described hereinafter.
An MIS type thin film semiconductor device according to the present invention may vary in structure as follows.
(1) An MIS type thin film semiconductor device having a gate electrode which is formed on a predetermined polycrystalline semiconductor film through a gate insulating film.
(2) An MIS type thin film semiconductor device having a gate electrode which is formed below a predetermined polycrystalline semiconductor film through a gate insulating film.
(3) An MIS type thin film semiconductor device having a gate electrode which is formed on the side of a predetermined polycrystalline semiconductor film through a gate insulating film.
According to a second aspect of the present invention, there is provided a thin film semiconductor device which has an insulating substrate, a first semiconductor film which is a polycrystalline semiconductor film, a gate electrode formed on the first semiconductor film through a gate insulating film, first charge transmitting and receiving mean and second charge transmitting and receiving means formed on the first semiconductor film at a predetermined interval therebetween, and a channel region formed between the first and second charge transmitting and receiving means, wherein
the main orientation of the first semiconductor film constituting the channel region is {110} with respect to the main surface of the insulating substrate or the gate insulating film; and the first semiconductor film is essentially composed of crystal grains having an axis in a longitudinal direction of 45° or less with respect to a direction for connecting the first and second charge transmitting and receiving means in the channel region. This thin film semiconductor device is a more practical embodiment of the present invention.
In the thin film semiconductor device of the present invention, the first semiconductor film comprises a small inclination grain boundary having an angle of 75° or less with respect to a direction for connecting the first and second charge transmitting and receiving means.
According to a third aspect of the present invention, there is provided a thin film semiconductor device which has an insulating substrate, a first semiconductor film which is a polycrystalline semiconductor film, a gate electrode formed on the first semiconductor film through a gate insulating film, first charge transmitting and receiving mean and second charge transmitting and receivi
Hatano Mutsuko
Kimura Yoshinobu
Park Seong-Kee
Yamaguchi Shin'ya
Antonelli Terry Stout & Kraus LLP
Estrada Michelle
Fourson George
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