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
2000-01-10
2001-08-14
Ngô, Ngân V. (Department: 2814)
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, C257S066000, C257S350000
Reexamination Certificate
active
06274888
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device, a liquid crystal display device (hereinafter referred to as a liquid crystal display device) employing the semiconductor device and methods of fabricating the semiconductor device and the liquid crystal display device, and in particular to techniques of fabricating a thin film transistor (hereinafter referred to as a TFT) comprising a polycrystalline semiconductor on an insulating substrate.
There is a technique for fabricating peripheral circuits such as a driver circuit for driving pixels and a control circuit for controlling the driver circuit at the periphery of an insulating substrate on which pixels are fabricated in a liquid crystal display panel, for example.
The process for fabricating a polycrystalline Si TFT (hereinafter referred to as a p-Si TFT) of the peripheral circuits is intrinsically a hot-temperature process, but a low-temperature process for it is realized by using a process explained below.
The low-temperature process comprises formation of an amorphous silicon (hereinafter referred to as an a-Si) film, conversion of the a-Si film into a polycrystalline film by irradiation of excimer laser, formation of a gate insulating oxide film by plasma CVD or the like, formation of a gate electrode made of a metal or a metallic silicide by a sputtering method or the like, formation of source and drain regions by ion doping or ion implantation, and then ion activation by laser annealing.
The above crystallization of an a-Si film by excimer laser uses a phenomenon that irradiation of a UV light pulse of about 20 ns melts the a-Si film and then crystallization occurs as the a-Si film cools.
But with the conventional method, it is very difficult to control the grain sizes, orientations and positions of crystals in the polycrystalline film because of fast crystallization and non-equilibrium process.
The larger the grain sizes are, the better the performance of the p-Si TFT becomes, but the wider the spread in the grain sizes becomes and consequently the wider the variability of TFT characteristics becomes.
If the grain sizes are selected to be sufficiently smaller than the length of a channel of TFTs, the variability of the TFT characteristics becomes smaller, but the TFT characteristics are degraded.
The p-Si TFTs of the peripheral circuits in the liquid crystal panel are of the so-called SOI (Silicon-On-Insulator) type using an insulating substrate such as a glass substrate and are not capable of establishing a substrate potential, and consequently an adverse effect such as a projection called a “kink” occurs in a current-voltage characteristic curve especially of the p-Si TFT constituting the high-performance peripheral circuits.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device or an LCD provided with TFTs having a polycrystalline film uniform in orientation of crystalline grains and containing few unwanted impurities introduced in grain boundaries (hereinafter referred to merely as grain boundary impurities) and a channel region of the TFTs formed of a polycrystalline film comprising a small number of crystal grains each having a diameter larger than a length of a channel of the TFTs and each having a grain boundary thereof aligned parallel with a source-drain direction of the TFTs.
It is another object of the present invention to provide an LCD having a liquid crystal display panel provided with a peripheral circuit formed on a substrate of the liquid crystal display panel wherein TFTs constituting at least the peripheral circuit have a polycrystalline film uniform in orientation of crystalline grains in a plane parallel with a major surface of the substrate and containing few grain boundary impurities and a channel region of the TFTs formed of a polycrystalline film comprising a small number of crystal grains each having a diameter larger than a length of a channel of the TFTs and each having a grain boundary thereof aligned parallel with a source-drain direction.
It is another object of the present invention to provide a semiconductor device or an LCD having TFTs provided with a polycrystalline conductive layer in contact with a polycrystalline semiconductor layer forming an active area of each of the TFTs such that a potential of a substrate on which the TFTs are formed is established by the polycrystalline conductive layer.
To accomplish the above objects, in accordance with one embodiment of the present invention, there is provided a semiconductor device having a thin film transistor comprising: an insulating substrate, an island made of a polycrystalline semiconductor material and disposed on said insulating substrate, a conductive layer made of said polycrystalline semiconductor material and at least one of metals and metallic silicides and surrounding said island, a source region and a drain region spaced from said source region, said source region and said drain region being formed in said island, a gate electrode disposed on said island with an insulating film interposed between said island and said gate electrode, said gate facing a spacing between said source region and said drain region, wherein said polycrystalline semiconductor material forming said island and said conductive layer are fabricated by initially annealing a first amorphous semiconductor material deposited on said insulating substrate with a crystallization-inducing layer made of said at least one of metals and metallic silicides and having a hole corresponding to said island, said crystallization-inducing layer being disposed on a surface of said amorphous semiconductor material on at least one of a substrate side thereof and a side thereof opposite from said substrate side, and then by depositing a second amorphous semiconductor material on said first amorphous semiconductor and annealing said second amorphous semiconductor material.
To accomplish the above objects, in accordance with another embodiment of the present invention, there is provided a liquid crystal display device having a liquid crystal panel comprising a pair of insulating substrates, a liquid crystal layer sandwiched between said pair of insulating substrates, a plurality of pixels formed between said pair of insulating substrates and a peripheral circuit for driving said plurality of pixels and disposed at a periphery of at least one of said pair of insulating substrates, said peripheral circuit including a thin film transistor comprising: an insulating substrate, an island made of a polycrystalline semiconductor material and disposed on said insulating substrate, a conductive layer made of said polycrystalline semiconductor material and at least one of metals and metallic silicides and surrounding said island, a source region and a drain region spaced from said source region, said source region and said drain region being formed in said island, a gate electrode disposed on said island with an insulating film interposed between said island and said gate electrode, said gate facing a spacing between said source region and said drain region, wherein said polycrystalline semiconductor material forming said island and said conductive layer are fabricated by initially annealing a first amorphous semiconductor material deposited on said insulating substrate with a crystallization-inducing layer made of said at least one of metals and metallic suicides and having a hole corresponding to said island, said crystallization-inducing layer being disposed on a surface of said amorphous semiconductor material on at least one of a substrate side thereof and a side thereof opposite from said substrate side, and then by depositing a second amorphous semiconductor material on said first amorphous semiconductor and annealing said second amorphous semiconductor material.
To accomplish the above objects, in accordance with another embodiment of the present invention, there is provided a method of fabricating a semiconductor device including the steps of: depositing a first amorphous semiconductor film on a
Miyano Masanobu
Nagata Tetsuya
Ogino Toshio
Saito Masakazu
Suzuki Kenkichi
Antonelli Terry Stout & Kraus LLP
Hitachi Ltd
Ngo Ngan V.
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