Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2002-03-29
2004-09-21
Tran, Minhloan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S059000, C257S061000, C257S258000, C257S291000
Reexamination Certificate
active
06794682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device including a thin-film transistor used as a switching element, a method for manufacturing the same, and a radiation detector. More particularly, the invention relates to a semiconductor device for photoelectric conversion having pixels, each including a photoelectric transducer and a thin-film transistor, a method for manufacturing the same, and a radiation detector.
2. Description of the Related Art
Recently, modules using thin-film transistors are being used in various fields. Such modules include, for example, liquid-crystal display devices or organic EL (electroluminescent) displays, each using thin-film transistors as switching elements on an insulating surface of a substrate, large flat-panel sensors, each using thin-film transistors as switching elements on an insulating surface of a substrate, and the like. A large flat-panel sensor is used as a detector for radiation, such as X-rays, by forming a layer of a substance called a scintillator or a phosphor above the sensor.
Although the size of the substrate is increasing, intension to realize a small-size and high-precision semiconductor-device module using thin-film transistors is very strong, since such a module is used as a display device for a portable terminal, a cellular phone or the like. In such circumstances, in order to improve the performance of a thin-film transistor, it is desired to improve the transfer efficiency of the thin-film transistor and also improve the numerical aperture of the corresponding pixel by reducing the size of the thin-film transistor. The situation is the same for a flat-panel sensor, in which it is also necessary to maintain the sensitivity of the sensor while achieving high-speed driving.
At present, bottom-gate-type thin-film transistors in each of which a gate electrode is formed on an insulating substrate and a semiconductor layer is formed on the gate electrode is mostly used as thin-film transistors. The bottom-gate-type thin-film transistors are grossly classified into two types.
One type comprises thin-film transistors called a gap-etching type or a channel-etching type, as shown in FIG.
9
. In this type, after forming a gate electrode
2
on an insulating substrate
1
, an insulating film
3
, a semiconductor layer
4
and a doped semiconductor layer
5
are consecutively formed by CVD (chemical vapor deposition), and a thin-film transistor is formed by etching the doped semiconductor layer
5
at a gap portion of the thin-film transistor. In this gap-etching-type thin-film transistor, since the semiconductor layer
4
is formed thin, it is necessary to improve the distribution of etching at gap etching and make the thickness of the semiconductor layer
4
uniform during film formation.
Another type comprises thin-film transistors called, for example, a etching-stopper type or a channel-passivation type, as shown in FIG.
10
. In this type, after forming a gate electrode
2
on an insulating substrate
1
, an insulating film
3
, a semiconductor layer
4
, and a channel-protection film
8
comprising, for example, an insulating film, are consecutively formed by CVD. Then, the channel-protection film
8
is etched except for a portion corresponding to a gap portion of the thin-film transistor, followed by formation of a doped semiconductor layer
5
. Then, a thin-film transistor is formed by etching the doped semiconductor layer
5
at a gap portion of the thin-film transistor. In this etching-stopper-type thin-film transistor, although a semiconductor layer can be formed independent of the distribution of etching during gap etching, control when etching the insulating film
8
is important. A high-speed thin-film transistor is provided by stabilizing the etching rate, improvement of the distribution of etching, and the like.
In the etching-stopper-type thin-film transistor using an insulating film comprising, for example, a silicon-nitride film or the like, it is pointed out that, although it is possible to provide a high-performance thin-film transistor by forming a thin semiconductor layer, the number of processes increases, resulting in a large process time.
In the gap-etching-type thin-film transistor, it is pointed out that, although the manufacturing process is relatively simple, it is difficult to form a thin semiconductor film because a dopant is unintentionally injected to a predetermined depth from the surface of the semiconductor layer while the doped semiconductor layer is formed. If the thickness of the semiconductor layer is large, the operation of the thin-film transistor is slow.
It is considered that in any type of thin-film transistor, it is difficult to sufficiently improve the quality of a semiconductor film, serving as a channel, if the thickness of the semiconductor film is very thin, in consideration of the manufacturing process.
In any case, a thin-film transistor capable of performing a high-speed operation using a good-quality thin film as a semiconductor layer, serving as a channel, is being desired.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device having thin-film transistors capable of performing a high-speed operation, a method for manufacturing the same, and a radiation detector using the semiconductor device.
It is another object of the present invention to provide a semiconductor device having thin-film transistors having excellent transfer efficiency, a method for manufacturing the same, and a radiation detector using the semiconductor device.
It is still another object of the present invention to provide a semiconductor device having inexpensive thin-film transistors which can prevent a decrease in the sensitivity of photoelectric transducers when integrating the thin-film transistors with the photoelectric transducers, a method for manufacturing the same, and a radiation detector using the semiconductor device.
According to one aspect of the present invention, in a semiconductor device including bottom-gate-type thin-film transistors each of which includes a gate electrode provided on an insulating surface of a substrate, a semiconductor layer provided on the gate electrode via a gate insulating layer, a pair of doped semiconductor layers adjacent to the semiconductor layer, and source and drain electrodes consisting of a pair of conductors adjacent to corresponding ones of the pair of doped semiconductor layers, a thickness of portions of the semiconductor layer below the source and drain electrodes is smaller than a thickness of a portion of the semiconductor layer at a gap portion between the source and drain electrodes.
In this invention, the thickness of the portions of the semiconductor layer below the source and drain electrodes may be within a range of 30 nm-300 nm, and the thickness of the portion of the semiconductor layer at the gap portion may be within a range of 60 nm-1,500 nm.
The thickness of the portions of the semiconductor layer below the source and drain electrodes may be 0 nm.
The surface of the gap portion may be covered with a protective film covering the source and drain electrodes. The surface of the gap portion may be covered with a channel-protection film, and end portions of the channel-protection film may be covered with the source and drain electrodes.
The doped semiconductor layer may be formed on the semiconductor layer which has been thinned by etching.
In this invention, photoelectric transducers may also be provided on the insulating surface of the substrate.
Each of the photoelectric transducers may include a semiconductor layer made of a material which is the same as a material for the semiconductor layer at the gap portion of the thin-film transistor and whose thickness is the same as the thickness of the semiconductor layer at the gap portion. Each of the photoelectric transducers may include a semiconductor layer made of a material which is the same as a material for the semiconductor layer at the gap portion of the thin-film transistor and w
Mochizuki Chiori
Watanabe Minoru
Tran Minhloan
Tran Tan
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