Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1997-03-20
2001-01-30
Abraham, Fetsum (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S348000, C257S349000, C257S350000, C257S351000, C257S352000, C257S353000, C257S055000, C257S056000, C257S059000, C257S065000
Reexamination Certificate
active
06180982
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention disclosed in the specification relates to a thin film transistor and a method of making thereof. Further, the present invention relates to a method of making a display device of an active matrix type utilizing thin film transistors.
2. Description of Related Art
A thin film transistor has been known as a device for constituting an active matrix type liquid crystal display device. Particular attention is being paid to technologies utilizing a thin film transistor using a silicon thin film having crystallinity.
A thin film transistor using a silicon film having crystallinity is characterized in that a high speed operation is feasible and a CMOS (Complementary Metal Oxide Semiconductor) circuit can be constituted.
When a thin film transistor using a silicon thin film having crystallinity is used, an active matrix circuit and peripheral drive circuits for driving the active matrix circuit can be integrated on one sheet of a glass substrate (or quartz substrate) by making use of such a characteristic.
However, a crystalline silicon thin film provided in the current technology is not in a single crystal state but in a polycrystal state or a microcrystal state. Defects or impurities are included in such a film (referred to as crystalline silicon film) at a comparatively high level. Accordingly, there poses a problem where the structure of a bonded portion of different conductive materials is electrically inferior. The problem gives rise to a factor causing an aging change (generally amountable to deterioration) of an OFF current or properties in the operation of a thin film transistor.
For example, the problem where the OFF current (a current made to flow between a source and a drain in the OFF operation) is comparatively large is a problem common to thin film transistors of a P-channel and an N-channel type. Furthermore, the mobility of carriers in the P-channel type thin film transistor is lower than that of carriers of the N-channel type one. Also, there poses a problem in the N-channel type transistor where deterioration by hot carriers (deterioration thereof particularly at a bonded portion) is significant.
It is preferable to attain simultaneous resolution of the above-described problems when an integrated circuit using thin film transistors are constituted. Especially, when P-channel type and N-channel type transistors are simultaneously formed (separately formed) on a same substrate, a difference in characteristics between the P-channel type transistors and the N-channel type ones needs to correct.
The reason is that a circuit, (generally constituted based on a CMOS circuit) having excellent characteristics cannot be obtained when only the N-channel transistor or the P-channel transistor is provided with a low OFF current characteristic or is provided with a high mobility.
It is a problem of the present invention disclosed in the specification to provide a thin film transistor having a low OFF current value. Also, it is a problem thereof to provide thin film transistors of a P-channel type and an N-channel type where the difference in characteristics is corrected.
SUMMARY OF THE INVENTION
According to one aspect of the present invention disclosed in the specification, as illustrated in a specific constitution example of
FIG. 4
, there is provided a semiconductor device which is a P-channel type thin film transistor having a channel forming region
140
and a drain region
150
, wherein an impurity region
149
having a stronger p-type characteristics than the drain region is arranged between the channel forming region and the drain region.
The low OFF current characteristic can be obtained by arranging the impurity region
149
having the stronger P-type characteristics. The P-type behavior more potential than the P-type behavior of the drain region
150
signifies that the impurity region
149
is provided with the property as a P-type semiconductor more potential than that of the drain region
150
. The intensity of the property as the P-type semiconductor can be compared by a hole density (density of majority carriers) or conductance. That is, the P-type semiconductor having a high hole density and a high conductance has the stronger property as a P-type semiconductor. In
FIG. 4
, the relative degree of the intensity of the property as the P-type semiconductor is designated by notations P+ or P++.
In the above-described constitution, an impurity providing an N-type behavior is included in the region
149
and the drain region
150
. This is because an impurity providing the N-type behavior is simultaneously implanted in forming an N-channel type thin film transistor as illustrated by FIGS.
3
(A) and
3
(B).
As is apparent in reference to FIGS.
3
(A) and
3
(B), the concentration of the impurity providing the N-type behavior that is included in the region
149
having the potential P-type behavior is smaller than the concentration of the impurity providing the N-type behavior that is included in the drain region
150
.
Also, as illustrated in
FIG. 4
, the impurity ions for providing the P-type behavior are simultaneously implanted to the region
149
and the region
150
and therefore, the region
149
having the potential P-type behavior and the drain region
150
include the impurity providing the P-type behavior by concentrations substantially the same as each other.
According to another aspect of the present invention, as illustrated by a specific constitution example of
FIG. 4
, there is provided a semiconductor device which is a P-channel type thin film transistor having a channel forming region
140
and a drain region
150
, wherein the drain region
150
includes an impurity providing an N-type behavior, a region
149
including the impurity providing the N-type behavior by a concentration lower than that of the drain region
150
is arranged between the channel forming region
140
and the drain region
150
, and the region
149
including the impurity providing the N-type behavior by the concentration lower than that of the drain region
150
, is provided with the P-type behavior more potential than that of the drain region
150
.
According to another aspect of the present invention, as illustrated by a specific constitution example of
FIG. 4
, there is provided a semiconductor device where a P-channel type and an N-channel type thin film transistor are formed on a same substrate, an impurity region
145
having a P-type behavior more potential than that of the drain region is arranged between a channel forming region
134
and a drain region
146
in the P-channel type thin film transistor, and a low concentration impurity region
136
including the impurity providing the N-type behavior by a concentration lower than that of a drain region
127
is arranged between a channel forming region
137
and the drain region
127
in the N-channel type thin film transistor.
Although an example using a glass substrate is shown in
FIG. 4
, the above-described constitution can be utilized to a substrate having other insulating surface and an integrated circuit having a multilayered structure.
In the above structure, the impurity region
145
having the potential P-type behavior include the impurity providing the N-type behavior by a concentration substantially the same as that of the low concentration impurity region
136
, a source and a drain region
143
and
146
of the P-channel type thin film transistor, include the impurity providing the N-type behavior by a concentration substantially the same as those of a source and a drain region
129
and
127
of the N-channel type thin film transistor, and the impurity region
145
having the potential P-type behavior and the source and the drain regions
143
and
146
of the P-channel type thin film include the impurity providing the P-type behavior by substantially the same concentrations.
In the above-described constitution, the low concentration impurity region designated by numeral
136
of the N-channel type thin film tra
Teramoto Satoshi
Zhang Hongyong
Abraham Fetsum
Fish & Richardson P.C.
Semiconductor Energy Laboratory Co, Ltd
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