Thin-film transistor having lightly-doped drain structure

Details Thin-film transistor having lightly-doped drain structure Thin-film transistor having lightly-doped drain structure

2002-02-28

2004-05-18

Flynn, Nathan J. (Department: 2826)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S059000, C257S061000, C345S092000

Reexamination Certificate

active

06737717

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure of a semiconductor device having a semiconductor circuit comprised of semiconductor elements such as insulated gate transistors and a method for manufacturing the same. More particularly, the invention relates to a structure of a semiconductor device having a semiconductor circuit comprised of semiconductor elements having an LDD structure formed of organic resin and a method for manufacturing the same. Semiconductor devices according to the invention include not only elements such as thin film transistors (TFTs) and MOS transistors but also displays having a semiconductor circuit and electro-optical devices such as image sensors formed by such insulated gate transistors. In addition, semiconductor devices according to the invention include electronic equipments loaded with such displays and electro-optical devices.
2. Description of the Related Art
TFTs have been conventionally used as switching elements of active matrix liquid crystal displays (hereinafter abbreviated to read “AMLCD” ) The market is currently dominated by products having circuits formed by TFTs utilizing an amorphous silicon film as an active layer. Particularly, a widely used TFT structure is the reverse staggered structure, which allows simple manufacturing steps.
However, the accelerating trend toward AMLCDs with higher performance in recent years has resulted in more severe requirements on the operational performance (especially, operating speed) of TFTs. It has therefore become difficult to provide elements having sufficient performance utilizing TFTs comprising amorphous silicon films because of their operating speed.
Under such circumstances, TFTs utilizing polycrystalline silicon films (polysilicon films) have come into focus in place of amorphous silicon films, which has significantly accelerated the development of TFTs utilizing a polycrystalline silicon film as an active layer. Presently, some products have already been introduced.
Many reports have already been made on structures of reverse staggered TFTs utilizing a polycrystalline silicon film as an active layer. However, conventional reverse staggered structures have had various problems.
First, since an active layer as a whole employed in such structures is as very thin as about 50 nm, impact ionization occurs at the junction between a channel formation region and a drain region, which results in significant deteriorating phenomena such as the implantation of hot carriers. This necessitates the formation of an LDD region (light doped drain region).
It is expected that at least eight masks are required (for processes up to the formation of source and drain electrodes) to form such an LDD region in a conventional reverse staggered TFT structure.
As described above, in a conventional reverse staggered TFT structure, an LDD region must be formed in a horizontal plane on both sides or one side of a channel formation region, which makes it very difficult to form LDD regions with reproducibility.
It is an object of the invention to provide a technique for manufacturing semiconductor devices with high mass-productivity, reliability and reproducibility through very simple manufacturing steps.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a semiconductor device including a semiconductor circuit formed by semiconductor elements, characterized in that it comprises:
a gate line provided on an insulated surface;
a gate insulating film in contact with the gate line;
a channel formation region provided on the gate line with the gate insulating film interposed therebetween;
a low density impurity region in contact with the channel formation region;
a high density impurity region in contact with the low density impurity region;
a protective film in contact with the channel formation region; and
organic resin doped with a trivalent or pentavalent impurity in contact with the protective film.
According to a second aspect of the invention, there is provided a semiconductor device including a semiconductor circuit formed by semiconductor elements, characterized in that it comprises:
a gate line provided on an insulated surface;
a gate insulating film in contact with the gate line;
a channel formation region provided on the gate line with the gate insulating film interposed therebetween;
a low density impurity region provided on one side of the channel formation region;
a drain region constituted by a first high density impurity region in contact with the low density impurity region;
a source region constituted by a second high density impurity region provided on the other side of the channel formation region;
a protective film in contact with the channel formation region; and
organic resin doped with a trivalent or pentavalent impurity in contact with the protective film.
According to a third aspect of the invention, there is provided a semiconductor device including a semiconductor circuit formed by semiconductor elements, characterized in that it comprises:
a gate line provided on an insulated surface;
a gate insulating film in contact with the gate line;
a channel formation region provided on the gate line with the gate insulating film interposed therebetween;
a first low density impurity region and a second low density impurity region in contact with the channel formation region;
a high density impurity region on contact with the first low density impurity region and the second low density impurity region;
a protective film in contact with the channel formation region; and
organic resin doped with a trivalent or pentavalent impurity in contact with the protective film and in that the width of the first low density impurity region in the direction of the channel length is different from the width of the second low density impurity region in the direction of the channel length.
There is provided a configuration according to each of the above-described aspects, characterized in that the gate line has a single-layer or multi-layer structure and is made of one kind of element selected from among tantalum, copper, chromium, aluminum, molybdenum, titanium and silicon or a material primarily constituted by silicon doped with a p-type or n-type impurity.
There is provided a configuration according to each of the above-described aspects, characterized in that the trivalent or pentavalent impurity is phosphorus or boron.
There is provided a configuration according to each of the above-described aspects, characterized in that the organic resin has photosensitivity.
There is provided a configuration according to each of the above-described aspects, characterized in that the density of the trivalent or pentavalent impurity in the organic resin is 1×10
19
atoms/cm
3
or more.
There is provided a configuration according to each of the above-described aspects, characterized in that a catalytic element for promoting the crystallization of silicon is included in the high density impurity region.
It is also characteristic of the invention that the catalytic element is at least one or a plurality of elements selected from among Ni, Fe, Co, Pt, Cu and Au and that the catalytic element is Ge or Pb.
In the context of the present specification, “initial semiconductor film” is a generic term for semiconductor films which typically means semiconductor films having amorphous properties, e.g., amorphous semiconductor films (amorphous silicon films and the like), amorphous semiconductor films including micro-crystals and micro-crystal semiconductor films. Such semiconductor films include Si films, Ge films and compound semiconductor films (e.g., Si
x
Ge
1−x
(0<X<1) which is an amorphous silicon germanium film, “x” typically being in the range from 0.3 to 0.95. Such an initial semiconductor film can be formed using, for example, low pressure CVD, thermal CVD, PCVD, sputtering or the like.
In the context of the present specification, the term “crystalline semiconductor film” implies single crystal semiconductor films and semiconduc

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