Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2003-03-05
2004-04-06
Lam, Cathy (Department: 1775)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C428S209000, C428S620000
Reexamination Certificate
active
06717218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a layered structure of wire(s), a manufacturing method therefor, and a display apparatus including the layered structure of wire(s).
2. Description of the Related Art
Display apparatus using thin film transistors (hereinafter simply referred to as TFTs) as switching elements have been on the market these days. Recently organic electroluminescent (EL) display apparatus employing current-driven type organic light emitting diodes (hereinafter also referred to as OLED) that function as luminous elements are attracting attention as display apparatus to replace CRTs and LCDs. In display apparatus using organic electroluminescent (EL) elements, the TFTs are used also to drive the organic EL elements.
FIG. 5
is a cross-sectional view of a TFT in a display apparatus using an organic EL element. A TFT
200
has a stacked structure in the order of an insulating substrate
210
which is made of quartz glass or the like, an active layer
243
which is made of a polycrystalline silicon, a gate insulating film
212
which is made of SiO
2
(silicon oxide), and a gate electrode
242
which is made of a refractory metal such as molybdenum (Mo). The active layer
243
is provided with a channel
243
c
below the gate electrode
242
and a drain
243
d
and a source
243
s,
both formed by ion injection with the gate electrode
242
as a mask, on both sides of the channel
243
c.
The TFT
200
further includes an interlayer insulating film
215
which comprises a first interlayer insulating film
213
made of SiN and a second interlayer insulating film
214
made of SiO
2
, a drain electrode
253
and a source electrode
254
. The drain electrode
253
and the source electrode
254
are formed by filling aluminum (Al) or like metal in the contact holes provided corresponding to the drain
243
d
and the source
243
s,
respectively. The contact holes to be used in forming the drain electrode
253
and the source electrode
254
are formed by etching with buffered hydrofluoric acid or the like.
In the TFT
200
structured as described above, however, the first interlayer insulating film
213
is made of SiN which has a lower etching rate than SiO
2
that constitutes the gate insulating film
212
therebelow when using buffered hydrofluoric acid. Thus, if the contact holes are formed by wet etching using the buffered hydrofluoric acid, an overhang, where more of the gate insulating film
212
is etched as shown in
FIG. 6A
, will be formed at the boundary between the gate insulating film
212
and the first interlayer insulating film
213
. The formation of an overhang like this may cause a problem of increased contact resistance due to a level difference between the drain electrode
253
and the source electrode
254
, which are formed by their respective contact holes.
With display apparatus using organic EL elements, on the other hand, the driver TFTs including layered structure of wire(s) which serves as a power supply line for the organic EL elements are required to have higher reliability, which is to be realized by such measures as lowering resistance, reducing whiskers and hillocks or eliminating electromigration or stressmigration. To lower the resistance, the drain electrode
253
and the source electrode
254
are structured of a low-resistance metal such as the above-mentioned aluminum. Moreover, whiskers and hillocks are reduced by providing a protective metal layer made of a refractory metal such as molybdenum, in such a manner as to cover the wiring layer made of a low-resistance metal such as aluminum. The protective metal layer like this is formed thinner than the wiring layer made of a low-resistance metal in order to reduce the resistance of the layered structure of wire(s) as a whole and to reduce the unevenness of the panel surface.
When the drain electrode
253
and the source electrode
254
are formed of a wiring layer of a low-resistance metal and a protective metal layer, there may arise a problem of the protective metal layer severed due to a level difference created by the overhang formed in the contact hole as shown in FIG.
6
B. Moreover, as illustrated therein, a whisker may result at the severed portion. In particular, since the cathode of an organic EL element is formed all above the drain electrode
253
and the source electrode
254
, the whisker sprouting on the upper protective metal layer will cause a short circuit between these electrodes and the cathode of the organic EL element, thus rendering the display apparatus defective.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing circumstances and an object thereof is to provide a layered structure of wire(s) capable of reducing the occurrence of defective display apparatus by preventing a short circuit between electrodes. Another object of the present invention is to reduce the occurrence of whiskers in the layered structure of wire(s). Still another object of the present invention is to lower the resistance of the layered structure of wire(s).
According to the present invention, there is provided a layered structure of wire(s) provided in a contact hole formed in an insulating film in which a first insulating layer and a second insulating layer made of different material from each other are stacked in this order, and this layered structure of wire(s) includes: a first metal layer which is made of a refractory metal; a wiring layer, formed on the first metal layer, which is made of a metal whose resistance is lower than that of the refractory metal; and a second metal layer, formed on the wiring layer, which is made of a refractory metal and is thicker than the first insulating layer.
By forming the second metal layer thicker than the first insulating layer, it is possible that the second metal layer is formed without the occurrence of any severance even when an overhang is formed at a boundary between the first and second insulating layers at the contact hole. As a result, the formation of whiskers on the second metal layer can be prevented, so that no short circuit is caused between this layered structure of wire(s) and other electrodes.
The first insulating layer may be made of SiO
2
or SiON. Moreover, the second insulating layer may be made of SiN.
As the refractory metal, metal including a group
6
A element such as molybdenum (Mo), chromium (Cr) or tungsten (W), for example, may be used. Provision of such a metal layer can contribute to reducing the occurrence of whiskers and hillocks in an interconnection structure. Moreover, these group
6
A elements are characterized in that they exhibit less diffusion against the low-resistance metal. Furthermore, tantalum (Ta), vanadium (V) or niobium (Nb) may be used as the refractory metal. It is preferable that the refractory metal includes the molybdenum. In particular, the molybdenum can be processed with ease in its manufacturing process.
As a metal that constitutes the wiring layer, aluminum (Al), copper (Cu), silver (Ag), gold (Au), rhodium (Rh), iridium (Ir), nickel (Ni), platinum (Pt) or palladium (Pd) may be used, for example. The layered structure of wire(s) can be made low-resistant by using these metals as above. Among these metals, aluminum in particular, copper or silver whose resistivity is lower than that of aluminum is preferably used. It is particularly preferable that the wiring layer be made of metal including aluminum. Thereby, the adhesion of aluminum with the metal layer made of the refractory metal is enhanced because reactivity of aluminum is high, thus contributing to the improvement of a yield of the layered structure of wire(s).
According to the present invention, there is provided a layered structure of wire(s) provided in a contact hole formed in an insulating film in which a first insulating layer and a second insulating layer made of different material from each other are stacked in this order, and the layered structure of wire(s) includes: a first metal layer which is made of a refractory metal; a wiring lay
Hasegawa Isao
Suzuki Koji
Lam Cathy
Sanyo Electric Co,. Ltd.
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