Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
2000-11-16
2002-04-23
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
C257S072000, C257S350000, C257S412000, C257S762000, C257S763000, C257S764000, C257S765000, C438S155000
Reexamination Certificate
active
06376861
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thin film transistor and a method for fabricating the thin film transistor, more specifically to a highly reliable thin film transistor using low resistance wiring, and a method for fabricating the thin film transistor.
Liquid crystal display devices have an advantage that they are thin and light, and can be operated at low voltages with small current consumption. Recently liquid crystal display devices are widely used as displays of personal computers, etc.
Generally, the display panels of liquid crystal display devices are each constituted with two transparent glass substrates and liquid crystal sealed between the two transparent glass substrates. On one of the opposed sides of the two glass substrates a black matrix, a color filter, an opposed electrode, an alignment film, etc. are formed, and thin film transistors, picture element electrodes and an alignment film are formed on the other of the opposed sides of the two glass substrates.
Polarization plates are adhered respectively to the sides of the two glass substrates, which are opposite to the opposed sides. The polarization axes of the two polarization plates are arranged normal to each other to provide a liquid crystal display of normally white mode. That is, light is transmitted when no electric filed is applied to the liquid crystal, and when an electric field is applied to the liquid crystal, light is shaded. On the other hand, the polarization axes of the two polarization plates are parallel with each other to provide the liquid crystal device of normally black mode. That is, light is shaded with no electric field applied to the liquid crystal, and light is transmitted with an electric field applied to the liquid crystal.
A conventional liquid crystal display device will be explained with reference to
FIGS. 11A and 11B
.
FIG. 11A
is a plan view of a conventional active matrix substrate of the invert stagger type.
FIG. 11B
is a sectional view of the active matrix substrate along the line A-A′ in FIG.
11
A.
As shown in
FIG. 11B
, a gate electrode
118
is formed of an Al film
112
and an Mo film
116
on a glass substrate
110
. As shown in
FIG. 11A
, the gate electrode
118
is connected to a gate bus line
118
a
of the same conductor films.
Al film
112
is used as a material of the gate electrode
118
because Al has low electric resistance. In the conventional liquid crystal devices Cr, etc., which are metals of relatively high electric resistance and high melting point, have been used. Recently, in accordance with large scales and higher definition of the liquid crystal display devices, low resistance materials, such as Al, etc., are used.
The Mo film
116
is formed on the Al film
112
because Mo has high heat resistance and makes good electric contact with the Al film
112
with the other wiring, etc. The gate bus line
118
a
is connected to TAB through ITO (Indium Tin Oxide) in a region not shown, but is connected to other wiring, etc. through the Mo film
116
. The gate bus line
118
a
can have good electric contact.
A gate insulation film
120
is formed on the glass substrate
110
with the gate electrode
118
formed on. An amorphous silicon film
122
is formed on the gate insulation film
120
. A channel protection film
124
is formed on the amorphous silicon film
122
. An n
+
-amorphous silicon film
126
is formed on the amorphous silicon film
122
with the channel protection film
124
formed on. A source electrode
136
a
and a drain electrode
136
b
are formed of an Mo film
128
, an Al film
130
and an Mo film
134
on the n
+
-amorphous silicon film
126
. As shown in
FIG. 11A
, the drain electrode
136
b
functions as a data bus line.
A protection film
138
is formed on the gate insulation film
120
with the source electrode
136
a
and the drain electrode
136
b
formed on. A contact hole
140
arriving at the source electrode
136
a
is formed in the protection film
138
. A picture element electrode
142
is formed of ITO on the protection film
138
connected to the source electrode
136
a
through the contact hole
140
. The Al film
130
is connected to the picture element electrode
142
through the Mo film
134
, and the electric contact is good.
As described above, in the conventional liquid crystal display device shown in
FIGS. 11A and 11B
, Al, which is a low resistance metal, is used as a material of the gate bus line and the data bus line, and is suitable for larger scales and higher definition.
However, in the liquid crystal display device shown in
FIGS. 11A and 11B
, the side surfaces of the Mo film
116
of the gate electrode
118
is acute, which makes the step coverage of the gate insulation film
120
poor. Film quality of the gate insulation film
120
is interrupted near the side surfaces of the Mo film
116
. Accordingly, the gate insulation film
120
has low dielectric voltage resistance.
The side surfaces of the Mo film
134
of the source-drain electrodes
136
a
,
136
b
are acute, which makes it difficult to form the protection film
138
in good quality. The protection film
128
has low dielectric voltage resistance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thin film transistor which uses a low resistance metal as a material of the gate electrodes and wiring but can ensure high reliability, and a method for fabricating the thin film transistor.
The above-described object is attained by a thin film transistor comprising a gate electrode formed on a substrate, a gate insulation film formed on the gate electrode, a semiconductor layer formed on the gate insulation film, and a source electrode and a drain electrode formed on the semiconductor layer, the gate electrode, the source electrode or the drain electrode including a first conductor film, a second conductor film formed on the first conductor film, and a third conductor film formed on the second conductor film; the first conductor film being formed of a metal selected out of Al, Cu and Ag, or an alloy of a metal, as a main component, selected out of Al, Cu and Ag, and having side surfaces sloped; the second conductor film being formed of a film of Mo containing nitrogen, or an alloy of Mo containing nitrogen, and having side surfaces sloped; and the third conductor film being formed of Mo, or an alloy of Mo as a main component. The gate insulation film is formed on the gate electrode having the side surfaces generally sloped, whereby film quality of the gate insulation film is prevented from being interrupted near the side surfaces of the gate electrode. The gate insulation film can be highly reliable and can have high dielectric voltage resistance. The thin film transistor can be highly reliable.
The above-described object is attained by a thin film transistor comprising a gate electrode formed on a substrate, a gate insulation film formed on the gate electrode, a semiconductor layer formed on the gate insulation film, and a source electrode and a drain electrode formed on the semiconductor layer, the gate electrode, the source electrode or the drain electrode including a first conductor film, and a second conductor film formed on the first conductor film; the first conductor film being formed of a metal selected out of Al, Cu and Ag, or an alloy of a metal, as a main component, selected out of Al, Cu and Ag, and having side surfaces sloped; the second conductor film including a lower layer formed of a film of Mo containing nitrogen or an alloy of Mo, as a main component, containing nitrogen, and an upper layer formed of a film of Mo or an alloy of Mo, as a main component, and side surfaces of the lower layer being sloped. The gate insulation film is formed on the gate electrode having the side surfaces generally sloped, whereby film quality of the gate insulation film is prevented from being interrupted near the side surfaces of the gate electrode. The gate insulation film can be highly reliable and can have high dielectric voltage resistance. The thin film transistor can be
Kida Tetsuya
Komorita Akira
Watanabe Takuya
Yaegashi Hiroyuki
Fujitsu Limited
Greer Burns & Crain Ltd.
Ngo Ngan V.
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